The global probiotic market is worth over $60 billion. Capsules, drinks, powders, gummies, and fortified foods line pharmacy shelves with claims about gut health, immunity, mood, weight, and energy. Most of these claims are backed by evidence so narrow and strain-specific that it wouldn’t survive a pharmaceutical approval process, and yet they’ve become one of the most commercially successful categories in the entire supplement industry.

Several specific probiotic strains have genuine clinical evidence for specific indications. The problem is the gap between those narrow, conditional findings and what the industry sells on the basis of them, and the near-total absence from the conversation of the intervention with the most consistent microbiome evidence. That intervention costs nothing extra and has no marketing budget.

It’s food.

Subscribe now

What Your Microbiome Actually Is

The gut microbiome is a community of approximately 38 trillion microorganisms living in your gastrointestinal tract, outnumbering your own human cells by a ratio of roughly 1.3 to 1. These organisms, primarily bacteria but also archaea, fungi, and viruses, aren’t passengers. They’re metabolically active participants in almost every major physiological system you have.

They produce vitamins your body can’t synthesize on its own, including B12, K2, and folate. They synthesize the short-chain fatty acids (SCFAs, including butyrate, propionate, and acetate) that maintain the integrity of the intestinal wall, regulate immune cell behavior, and modulate systemic inflammation. They metabolize bile acids that influence cholesterol metabolism, hormone regulation, and fat absorption. They train and calibrate the immune system from infancy and continue to regulate immune responses throughout life.

Diversity matters more than any single species. A microbiome with hundreds of different species, each occupying a specific metabolic niche, is more resilient, more functionally capable, and more consistently associated with health outcomes than one dominated by a small number of species, regardless of which species those are.

This is the system the $60 billion probiotic industry is trying to sell you a solution for. The mismatch between that complexity and what a single-strain capsule can realistically do is the starting point for understanding the evidence.

Share

What Actually Builds a Diverse Microbiome

The strongest dietary evidence for microbiome health doesn’t come from supplementation research. It comes from dietary pattern research, and one pattern dominates the evidence base.

A 2024 systematic review published in BMC Medical Genomics analyzed the evidence from observational studies and clinical trials on the Mediterranean dietary pattern and gut microbiota composition.¹ The conclusion: adherence to the Mediterranean diet beneficially affects the gut microbiota profile across healthy populations and those with metabolic disorders, increasing the abundance of beneficial bacteria, promoting SCFA production, and reducing the proportion of pro-inflammatory species.¹

The mechanism is structural. The Mediterranean dietary pattern is, by design, a high-diversity, high-fiber, high-polyphenol way of eating. Extra virgin olive oil provides polyphenols that act as prebiotics, selectively feeding beneficial bacteria. Legumes (lentils, chickpeas, beans) provide fermentable fiber that bacteria convert into SCFAs butyrate and propionate. A wide variety of vegetables, fruits, whole grains, nuts, and seeds provides the substrate diversity that a diverse microbiome requires.

Plant diversity specifically matters. Data from the American Gut Project, one of the largest microbiome studies ever conducted and analyzing samples from more than 10,000 people, found that participants who ate more than 30 different plant species per week had significantly more diverse gut microbiomes than those who ate 10 or fewer.² The finding held across all dietary categories: omnivores, vegetarians, and vegans with high plant diversity all outperformed those with low plant diversity, regardless of their dietary label.

Subscribe now

Why Probiotic Marketing Is a Different Conversation From Probiotic Evidence

Here’s what the probiotic conversation almost never mentions: the evidence is entirely strain-specific. Evidence for one bacterial strain can’t be applied to another strain in the same species, let alone the same genus. “Lactobacillus” isn’t a probiotic. It’s a genus with hundreds of distinct species, each containing dozens or hundreds of individual strains, each with different properties and different effects.

When a product says “contains Lactobacillus cultures,” it’s telling you almost nothing clinically useful. The relevant questions are: which specific strain, at what dose, with what viable count at time of consumption, studied in which population, for which specific outcome? Almost no consumer probiotic product answers those questions on its label, because answering them honestly would make most of the implied health claims impossible to sustain.

The paid section covers what the evidence genuinely supports, as opposed to what the marketing implies: which strains have replicated peer-reviewed evidence, for which specific indications, and for whom the evidence is genuinely relevant. It also covers what, beyond diet, actually moves the needle on microbiome health, and the three questions worth asking before spending money on any probiotic product.

Read more

Brain fog is one of the most common complaints in clinical practice and one of the most dismissed. People describe it as thinking through wet concrete, losing words mid-sentence, reading the same paragraph four times. Clinicians often have nothing concrete to offer. The standard blood tests come back normal. The problem gets attributed to stress, aging, or not sleeping well enough.

That explanation may be partially correct. The problem is that it tells you nothing actionable.

Brain fog has biological causes that show up on standard laboratory tests. Most of those tests aren’t ordered unless you specifically ask for them. The five causes covered in this post account for the majority of reversible cognitive slowdown in otherwise healthy adults.

Subscribe now

Why Standard Blood Tests Miss the Problem

When someone goes to their doctor with brain fog, the typical response is a standard blood panel: a complete blood count, fasting glucose, TSH (thyroid-stimulating hormone, a marker of thyroid function), and a basic metabolic panel. In most cases, everything comes back in the normal range.

Normal on a standard panel doesn’t mean the brain is working well. It means you don’t have anemia, overt diabetes, or severely abnormal thyroid levels. Those are very different things.

The tests most likely to explain cognitive symptoms sit just outside what gets ordered routinely: a high-sensitivity inflammation marker, fasting insulin alongside fasting glucose to assess how the brain’s fuel system is working, a complete thyroid panel rather than just the one screening test, ferritin (the iron storage marker) checked against a meaningful threshold rather than the lab’s minimum, and a morning cortisol to look at the stress hormone axis. None of these appear on a standard annual panel. All of them can be ordered by a GP with a single request.

Share

Five Causes, All Reversible

All five work through different biological pathways.

Brain inflammation activates the brain’s own immune cells in a way that directly slows thinking and memory. Insulin resistance in the brain disrupts how the memory and attention centers receive their signals. Thyroid dysfunction slows the speed at which nerve signals travel and reduces energy in brain cells. Low iron depletes the raw material the brain needs to make the chemical that drives focus and working memory. Poor sleep prevents the brain’s nightly cleanup system from running, causing waste products to build up.

None of these require a brain scan or a specialist to investigate. Each one has a blood test that points to it. And each one gets better once it’s correctly identified.

The paid section covers all five in full clinical detail: the mechanism, the specific lab test, the threshold worth discussing with your doctor, and a ready-to-use script for the appointment. It closes with a downloadable brain fog symptom and lab tracker you can fill in over two weeks and bring with you.

Read more

For most of human history, aging was treated as a single inevitable process. Something that simply happened to the body over time, too deeply embedded in biology to be meaningfully interrupted. The best available response was early detection of what went wrong, then treatment. The idea that the underlying process itself could be measured, slowed, or in some cases partially reversed was, until recently, a fringe position.

That position is now the scientific mainstream.

In 2023, a paper published in Cell described aging not as one process but as twelve distinct, interconnected biological phenomena, each one measurable and several of them significantly affected by the things we do and don’t do every day.¹

The paper built on a 2013 framework by the same research group, which had identified nine hallmarks. A decade of evidence prompted them to add three more: disabled macroautophagy, chronic inflammation, and dysbiosis.

Every one of the twelve hallmarks meets three criteria: it manifests progressively with age, its acceleration experimentally accelerates aging, and its deceleration or reversal is achievable through intervention.

Not all twelve respond equally to lifestyle. That’s what most longevity content skips. But several are substantially affected by how you exercise, eat, sleep, and manage stress.

Subscribe now

Why Twelve? And Why Does the Number Matter?

The expansion from nine to twelve hallmarks reflected how the field now understands aging: not as a linear decline but as a network of interacting failures.

The original nine captured the molecular and cellular damage that accumulates with age. The three additions, disabled autophagy (the cellular recycling system), chronic inflammation (the smoldering immune state that drives virtually every age-related disease), and dysbiosis (the progressive disruption of the gut microbiome), recognized that aging’s downstream consequences are themselves drivers. They create feedback loops that accelerate the upstream damage.

Most people, when they hear about the hallmarks of aging, picture a checklist of twelve separate problems. The framework is a network where each process feeds the others. Improving one hallmark reduces the burden on the rest.

The same three or four lifestyle inputs show up repeatedly across the evidence because they intersect with multiple nodes in this network simultaneously.

Share

The Three-Group Architecture

The twelve hallmarks are organized into three groups that reflect how directly each one initiates the aging process.¹

Primary hallmarks are the upstream initiators: the molecular damage that accumulates first and drives everything downstream.

Genomic instability is the accumulation of DNA damage over time, including double-strand breaks, point mutations, and chromosomal rearrangements from oxidative stress, radiation, toxins, and the inevitable errors of DNA replication and repair.

Telomere attrition is the progressive shortening of the protective caps at the ends of chromosomes with each cell division. When telomeres get short enough, the cell reads the signal as DNA damage and either stops dividing or triggers cell death.

Epigenetic alterations are changes in the chemical tags and structural configurations that determine which genes are switched on or off in each cell type. With age, this pattern drifts, silencing genes that should stay active and activating genes that should stay silent.

Loss of proteostasis is the failure of the protein quality control system: the network of chaperones, repair enzymes, and recycling pathways that maintain the correct folding and function of every protein in every cell. Misfolded proteins accumulate into the toxic aggregates found in Alzheimer’s disease, Parkinson’s disease, and most other age-related neurodegenerative conditions.

Disabled macroautophagy is the impairment of the cell’s recycling machinery, the process through which damaged proteins and dysfunctional organelles are packaged and delivered for degradation and reuse. When autophagy declines, cellular waste accumulates and the quality of every organelle, including the mitochondria, deteriorates.

Antagonistic hallmarks are processes that are protective in youth but become damaging when they persist beyond their intended context.

Deregulated nutrient-sensing describes the desensitization of the cellular signaling pathways that translate energy availability into decisions about growth, repair, and stress resistance. In youth, these pathways toggle appropriately. With age, the growth signals stay chronically elevated, suppressing the repair programs that matter for longevity.

Mitochondrial dysfunction is the declining capacity of the cell’s energy-producing organelles. Mitochondria generate ATP (adenosine triphosphate), the cell’s energy currency. With age, mitochondrial number falls, function deteriorates, and their quality control mechanism breaks down. Dysfunctional mitochondria leak reactive molecules that damage DNA and amplify inflammation throughout the system.

Cellular senescence is the state in which damaged or stressed cells stop dividing and enter permanent cell cycle arrest. In youth, senescent cells are cleared by the immune system quickly. With age, clearance fails and they accumulate. They secrete a cocktail of inflammatory signals and enzymes collectively called SASP (the senescence-associated secretory phenotype), which damages neighboring tissue, disrupts stem cell function, and spreads dysfunction through the surrounding environment.

Integrative hallmarks are the downstream manifestations: the systemic consequences of accumulated upstream damage that then become drivers themselves.

Stem cell exhaustion is the loss of tissue renewal capacity that follows from the damage above. Stem cells in aging tissues become fewer, slower, and less capable of generating healthy replacement cells.

Altered intercellular communication is the breakdown of signaling between cells, tissues, and organs. Hormonal signals become noisier. Inflammatory signals spread farther. The coordination that keeps organ systems functioning in relation to each other deteriorates.

Chronic inflammation, called inflammaging in the aging literature, is the persistent, low-grade inflammatory state that accumulates with age. Unlike the acute inflammation that resolves an injury, inflammaging never turns off. It sits upstream of cardiovascular disease, Alzheimer’s disease, type 2 diabetes, sarcopenia (age-related muscle loss), and most age-related cancers. It’s driven by senescent cells, by dysbiosis, by mitochondrial dysfunction, and by the gradual failure of the immune system’s self-regulation.

Dysbiosis is the progressive disruption of the gut microbiome, the trillions of microorganisms that regulate immune function, produce vitamins and short-chain fatty acids, metabolize bile acids and dietary compounds, and maintain the integrity of the intestinal barrier. Age-related dysbiosis reduces microbial diversity, increases the proportion of pro-inflammatory species, and drives the intestinal permeability that allows bacterial fragments into the bloodstream, amplifying systemic inflammation.

Subscribe now

The Network Effect

These twelve processes age you together.

Mitochondrial dysfunction generates the oxidative stress that damages DNA, feeding genomic instability. That instability accelerates epigenetic drift. Cellular senescence releases SASP signals that suppress autophagy and drive chronic inflammation. Dysbiosis amplifies that inflammation and compromises the intestinal barrier. Chronic inflammation accelerates senescence in previously healthy cells, shortening their telomeres and disrupting their proteostasis. The damaged cellular environment then depletes stem cell reserves faster than they can replenish.

This mutual amplification explains why certain lifestyle interventions produce benefits that seem disproportionately large. Exercise addresses multiple hallmarks through multiple mechanisms simultaneously. Reducing mitochondrial dysfunction, chronic inflammation, and cellular senescence at once produces compounding benefits, because each hallmark improved reduces the load on the others.

The same pattern runs in the other direction. A lifestyle that accelerates one hallmark, say chronic sleep deprivation or a diet high in ultra-processed foods, doesn’t damage that one process in isolation. It loads the whole network.

Share

What the Twelve Hallmarks Mean for How You Age Right Now

Biological aging is not uniform. Two people born on the same day can have measurably different biological ages, and the gap is large enough to matter clinically. Epigenetic clocks, which estimate biological age from patterns of chemical marks on DNA, have documented differences of ten to twenty years between people of the same chronological age, differences that correlate with disease risk, functional capacity, and mortality.¹ These differences are driven largely by lifestyle inputs, not genetics.

The hallmarks also explain why diseases that look unrelated share the same upstream causes. Alzheimer’s disease, type 2 diabetes, cardiovascular disease, and most common cancers don’t coincidentally cluster in older adults. They cluster because they share a common set of upstream drivers. The hallmarks of aging are those drivers. Addressing them and preventing specific diseases are the same project, approached at the level of mechanism rather than diagnosis.

Sustained lifestyle changes tend to produce improvements that are faster and broader than expected, precisely because the network feeds itself in both directions.

Subscribe now

The Part Most Longevity Content Skips

Not all twelve hallmarks respond to lifestyle equally. Some are substantially modifiable. Some are moderately modifiable. Some are largely determined by genetics and cumulative chance, biology that lifestyle can influence at the margin but not control.

A framework that treats all twelve as equally addressable sends effort in the wrong direction.

The paid section below organizes the twelve hallmarks by modifiability. It starts with the five where lifestyle evidence is most robust, covers specific mechanisms and specific interventions, works through the moderately responsive hallmarks, and is honest about the three where lifestyle plays a supporting role rather than a determining one.

It also addresses the priority question: if you had to choose three interventions that touch the greatest number of hallmarks with the most consistent evidence, what are they?

The downloadable longevity habits self-assessment at the end lets you score your current inputs across each modifiable area and identify where the highest-return adjustments are.

Read more

Dementia is widely assumed to be the result of genetic fate and inevitable aging. Most people believe there is little they can do about it. The most comprehensive synthesis of dementia research ever published says something different.

The standing Commission on Dementia Prevention, Intervention, and Care published its third major report in 2024 — an update incorporating new evidence from thousands of studies, two additional risk factors, and a revised calculation of how much dementia is attributable to factors we can actually change.¹

That figure has been debated and contextualized since its publication. It doesn’t mean that dementia is easy to prevent, or that addressing one factor eliminates risk, or that lifestyle change alone can overcome a high genetic burden. What it means is that nearly half of dementia cases occur in the context of biological and behavioral conditions that medicine and public health have tools to address. And that the window for most of these interventions is not old age, it’s midlife.

Subscribe now

What “Population Attributable Fraction” Actually Means

The 45% figure is a population attributable fraction (PAF) — a statistical estimate of how many dementia cases in a population could theoretically be prevented if a given risk factor were completely eliminated. It’s a measure of population-level opportunity based on the current prevalence of each risk factor and its estimated relative risk for dementia.

The individual PAFs for each factor don’t sum to 45%, they overlap, because risk factors are interconnected. The Commission uses a method that accounts for this overlap to produce the combined estimate. Addressing hearing loss also reduces social isolation. Treating depression also reduces physical inactivity. Managing hypertension also reduces obesity-related vascular risk. The web of risk factors means that one intervention can address multiple pathways simultaneously.

The 14 risk factors are organized across three life stages, reflecting when each factor exerts its strongest influence on the developing and aging brain.¹

Share

The Window That Matters Most Is Not the One You Think

Most people associate dementia with what happens after 75. The 2024 Commission update shifted four risk factors from late life to midlife, reflecting stronger evidence that their influence on brain health operates primarily during the decades of the 40s, 50s, and 60s.¹ This means the age at which dementia prevention is most impactful is not the decade before symptoms appear. It’s the two to three decades before they could appear. A 50-year-old who begins addressing these factors isn’t too early. They may already be overdue.

The downloadable checklist at the end of this post organizes all 14 risk factors by life stage, with specific actions for each one. It’s designed to be taken to a doctor’s appointment and used as a structured conversation tool.

Subscribe now

The 14 Risk Factors — What They Are, Why They Matter, and What to Do

Early Life

1. Less Education (5% of Dementia Cases)

Education builds cognitive reserve — the brain’s capacity to sustain damage before it produces clinical symptoms. More years in formal education, and higher-quality education, produce denser neural networks, more synaptic connections, and a larger functional buffer against the neurodegeneration that accumulates with age. A person with high cognitive reserve can sustain the same degree of Alzheimer’s pathology as a person with low cognitive reserve and remain cognitively functional far longer.¹

The education window has passed for most adults. But the underlying mechanism — cognitive reserve — continues to respond to stimulation throughout life. Lifelong learning, cognitive engagement, acquiring new skills (especially those that are genuinely challenging and unfamiliar), bilingualism, and complex professional or creative work all appear to build reserve in adulthood. The brain’s plasticity doesn’t end at graduation.

Action: Maintain cognitive engagement throughout adult life — not with puzzles and brain training apps (evidence is weak), but with genuine learning that requires sustained effort: new languages, musical instruments, technical skills, formal education, or intellectually demanding work.

Subscribe now

Midlife (40–65)

2. Hearing Loss (7% of Dementia Cases)

Hearing loss is the largest single modifiable risk factor for dementia in the 2024 Commission framework. The mechanisms are multiple: untreated hearing loss reduces auditory stimulation to the brain, requires disproportionate cognitive resources for processing degraded sound signals (reducing capacity available for memory and executive function), and — critically — drives social withdrawal that compounds isolation and reduces engagement.¹

A multicentre randomized controlled trial — the Aging and Cognitive Health Evaluation in Elders (ACHIEVE) study, published in The Lancet in 2023 — tested whether hearing intervention could reduce cognitive decline in 977 older adults with untreated hearing loss over three years. In the pre-specified group of participants at higher risk of cognitive decline, the hearing intervention slowed cognitive decline by 48% compared to a health education control.² The full trial population result was not statistically significant, suggesting the benefit is concentrated in those with elevated risk — which is also the population most likely to benefit most from early identification.

Action: Have a hearing test from age 50 if you haven’t already, and every 3 to 5 years thereafter. If hearing loss is found, use hearing aids. Medicare and many insurance plans cover audiological assessment. The evidence strongly supports treatment — untreated mild-to-moderate hearing loss is not a benign condition.

Leave a comment

3. High LDL Cholesterol (7% of Dementia Cases)

Added to the framework in 2024, based on evidence from large cohort studies involving more than 1 million participants and a Mendelian randomization meta-analysis of 27 studies confirming a causal relationship.¹

Elevated low-density lipoprotein (LDL) cholesterol in midlife — not just in the context of cardiovascular disease — independently increases dementia risk. The mechanisms include promotion of cerebrovascular disease (contributing to vascular dementia), and potential involvement in amyloid pathway dysregulation relevant to Alzheimer’s pathology.¹

Action: Have a full lipid panel (total cholesterol, LDL, high-density lipoprotein, and triglycerides) from age 40 to 45. If LDL is elevated, the first-line intervention is dietary — specifically reducing saturated fat and ultra-processed food, and adopting a Mediterranean dietary pattern, which has the strongest evidence base for LDL reduction without medication. If dietary intervention is insufficient given overall cardiovascular risk profile, discuss statin therapy with your doctor.

Share

4. Smoking (5% of Dementia Cases)

In the 2024 update, smoking was reclassified as a midlife risk factor, reflecting evidence that it exerts its greatest influence on brain health during the 40s and 50s rather than in old age.¹

Smoking accelerates cerebrovascular disease, promotes neuroinflammation, generates oxidative stress that damages neuronal DNA and mitochondria, and reduces cerebral blood flow. The mechanistic overlap with virtually every other dementia risk factor makes it a compounding risk: smokers are more likely to have hypertension, higher LDL, physical inactivity, and cardiovascular disease.

Cessation at any age reduces risk. Former smokers have lower dementia risk than current smokers, and the trajectory improves with years since cessation.

Action: Stop smoking. Discuss cessation support with your doctor — combined pharmacotherapy and behavioral support has the highest evidence base for cessation success. No amount of smoking is neurologically safe, and the risk compounds with every year of continued exposure.

5. Depression (3% of Dementia Cases)

Depression was also moved to midlife in 2024. The relationship between depression and dementia is bidirectional and biologically direct: chronic depression activates the HPA (hypothalamic-pituitary-adrenal) axis, producing sustained cortisol elevation that causes measurable hippocampal atrophy — the hippocampus being the brain structure most critical for memory formation and most affected in early Alzheimer’s disease.¹ Depression also reduces social engagement, physical activity, sleep quality, and dietary adherence — compounding risk through multiple other pathways.

Crucially, the Commission treats depression as a causal risk factor, not simply an early symptom of dementia. Treating depression reduces dementia risk.

Action: Treat depression. This means evidence-based intervention — cognitive behavioral therapy, pharmacotherapy, or combined treatment. Depression in midlife has measurable downstream neurological consequences that extend decades.

Subscribe now

6. Traumatic Brain Injury (3% of Dementia Cases)

Traumatic brain injury (TBI) increases dementia risk through several mechanisms: neuroinflammation triggered by the initial injury, tau protein phosphorylation (the same process central to Alzheimer’s pathology), white matter damage that disrupts neural network integrity, and potential blood-brain barrier disruption that allows peripheral inflammatory signals to enter the brain.¹ The risk is cumulative — repeated head injuries (as in contact sports) produce greater risk than single events.

Action: Wear a helmet for cycling, skiing, and contact sports. Implement fall prevention strategies as you age — this is both a TBI risk and a bone health risk. If you have experienced a significant head injury, discuss this history with your doctor when considering cognitive screening.

7. Physical Inactivity (2% of Dementia Cases)

Exercise is one of the most consistent interventions across the dementia prevention literature, operating through multiple converging mechanisms: increased production of BDNF (brain-derived neurotrophic factor — the protein most responsible for neuroplasticity and new neuron formation), preserved hippocampal volume, improved cerebrovascular function, insulin sensitivity, reduced inflammation, and better sleep architecture.¹ Physical inactivity was moved to midlife in 2024.

Action: 150 minutes of moderate-intensity aerobic exercise per week, combined with resistance training at least twice weekly. The hippocampal benefits of aerobic exercise are most consistently documented for sustained moderate-to-vigorous aerobic activity — not light walking alone.

Share

8. Diabetes (2% of Dementia Cases)

Diabetes moved to midlife in 2024. Hyperglycemia — chronically elevated blood glucose — drives cerebral microvascular disease that produces the vascular component of dementia, promotes amyloid accumulation through impaired clearance, and impairs neuronal insulin signaling. Some researchers describe Alzheimer’s disease as having features of “type 3 diabetes” given the central role of neuronal insulin resistance in its pathophysiology.¹

The window for prevention is insulin resistance — the state detectable a decade or more before type 2 diabetes develops, when fasting glucose and standard tests still appear normal. HOMA-IR (Homeostasis Model Assessment of Insulin Resistance — calculated from fasting insulin and fasting glucose) is the early detection tool. Lifestyle intervention at the insulin resistance stage is highly effective.

Action: Have your fasting insulin checked alongside fasting glucose and calculate your HOMA-IR. If elevated, the Diabetes Prevention Program lifestyle framework (modest weight loss and 150 minutes of weekly physical activity) reduced progression from prediabetes to type 2 diabetes by 58%, and the brain benefits of early intervention are substantially greater than those of late-stage glycemic management.

Leave a comment

9. Hypertension (2% of Dementia Cases)

Midlife hypertension — blood pressure above 130/80 mmHg during the 40s and 50s — is a stronger dementia risk factor than hypertension developing in old age. The mechanism involves reduced cerebral perfusion pressure, white matter hyperintensities (areas of microvascular damage visible on brain imaging), and accelerated cerebral small vessel disease.¹

The implication: blood pressure that is “acceptable” by older clinical standards but elevated by current thresholds (above 130/80 mmHg) is not neurologically benign in midlife. Treatment at this stage has substantially greater neuroprotective benefit than treatment initiated after 70.

Action: Know your blood pressure. If it’s consistently above 130/80 mmHg in midlife, treat it — lifestyle first (sodium reduction, exercise, dietary pattern, weight), and medication if lifestyle measures are insufficient. Discuss target blood pressure with your doctor specifically in the context of long-term brain health.

Subscribe now

10. Obesity (1% of Dementia Cases)

Midlife obesity (body mass index — BMI — above 30) increases dementia risk through visceral fat’s role as an inflammatory organ, through its contribution to insulin resistance and vascular risk, and through hormonal and metabolic pathways that dysregulate brain energy metabolism.¹

The individual PAF of 1% may understate the risk, because obesity contributes causally to hypertension, diabetes, physical inactivity, and depression — all of which carry their own PAFs. Addressing visceral fat addresses multiple risk factors simultaneously.

Action: Waist circumference is more clinically meaningful than BMI for this risk factor — it’s a more direct measure of visceral adiposity. Target: below 88 cm (35 inches) for women, below 102 cm (40 inches) for men. Metabolic health (insulin sensitivity, blood pressure, lipids) matters more than scale weight.

Share

11. Excessive Alcohol (1% of Dementia Cases)

The Commission defines excessive alcohol as more than 12 US units per week. Alcohol is directly neurotoxic at high doses, causes thiamine (vitamin B1) deficiency that can produce Wernicke-Korsakoff syndrome, drives liver disease that amplifies systemic inflammation, and compounds vascular risk.¹

Action: Stay below 12 US units per week. One US unit equals approximately 14g of pure alcohol — one standard 5-oz glass of wine (12% ABV — alcohol by volume), one 12-oz regular beer (5% ABV), or one 1.5-oz shot of spirits (40% ABV). If you regularly exceed this, discuss reduction strategies and alcohol use screening with your doctor.

Late Life (65+)

12. Air Pollution (2% of Dementia Cases)

Fine particulate matter (PM2.5 — particles smaller than 2.5 microns) is the primary mechanism: particles small enough to enter the bloodstream can cross the blood-brain barrier and trigger neuroinflammation, and can also enter the brain directly via the olfactory pathway. Multiple large cohort studies link long-term PM2.5 exposure to accelerated cognitive decline and higher dementia incidence.¹

Action: Use a HEPA (High Efficiency Particulate Air) filter in your home, particularly in bedrooms where you spend sustained hours. Check your local air quality index on high-pollution days and limit outdoor exposure. Avoid exercising near heavy traffic. Ensure good ventilation and monitor indoor air quality.

13. Social Isolation (2% of Dementia Cases)

Social isolation reduces cognitive stimulation, promotes depression, increases chronic stress with sustained cortisol elevation, reduces engagement of the default mode and social cognition brain networks, and amplifies the cognitive impact of hearing and vision loss.¹ The effects are neurological, not merely psychological.

Action: Maintain regular, meaningful social engagement — not digital contact alone, but in-person interaction that demands social cognition. If hearing or vision loss is reducing social participation, treating those conditions is the most direct intervention. Loneliness and social isolation are not personality traits; they are modifiable risk factors with neurological consequences.

Leave a comment

14. Untreated Vision Loss (2% of Dementia Cases)

Added in 2024 based on evidence from two large meta-analyses.¹ The mechanism is analogous to hearing loss: uncorrected vision loss reduces the quality of sensory input to the brain, reduces environmental engagement and cognitive stimulation, increases risk of falls and TBI, and promotes social withdrawal and depression. Cataracts, refractive error, and age-related macular degeneration are all potentially correctable.

Action: Have a comprehensive eye examination from age 50, and every 1 to 2 years from age 60. Wear corrective lenses if prescribed. If cataracts are affecting visual function, discuss surgical timing with your ophthalmologist — cataract surgery is associated with reduced dementia risk in observational studies, consistent with the Commission’s framework.

Subscribe now

The Priority Framework

Fourteen factors can feel overwhelming. The Commission’s own interpretation is useful: addressing any single factor produces a 1 to 7% reduction in population-level dementia. Addressing all 14 produces 45%. But the practical value is not chasing all 14 simultaneously, it’s identifying which ones apply to you, and prioritizing those where intervention is most accessible and where the PAF is largest.

• The highest-yield cluster: Hearing loss (7%), high LDL cholesterol (7%), and smoking (5%) account for 19% of dementia cases combined. All three are either testable by a standard clinical assessment or correctable with available tools. For most adults over 50, this is where to start.

• The vascular cluster: Hypertension (2%), diabetes (2%), and obesity (1%) share a common pathway through cerebrovascular and metabolic health. Addressing all three through the lifestyle framework that also addresses physical inactivity covers five risk factors through one set of behavioral changes — exercise, dietary pattern, weight management.

• The social and sensory cluster: Social isolation (2%), vision loss (2%), and hearing loss (7%) are interconnected. Treating hearing and vision loss typically reduces social isolation as a secondary consequence — one intervention addressing three risk factors.

None of these interventions requires a specialist or an expensive pharmaceutical. Most require a blood test, a test of hearing or vision, and a conversation with a primary care doctor. The gap between the evidence and what happens in practice is behavioral, and this post exists to close that gap for people who want to act on it.

Share

Your Dementia Prevention Checklist

The downloadable checklist covers all 14 risk factors organized by life stage, with a specific action item for each, a “current status” column to fill in, and the questions to bring to your doctor.

Leave a comment

To your zenith within,

Sara Redondo, MD, MS

References:

1. Livingston G, Huntley J, Liu KY, et al. Dementia prevention, intervention, and care: 2024 report of the Lancet standing commission. Lancet. 2024;404(10452):572-628. doi:10.1016/S0140-6736(24)01296-0

2. Lin FR, Pike JR, Albert MS, Arnold M, Burgard S, Chisolm T, Couper D, Deal JA, Goman AM, Glynn NW, Gmelin T, Gravens-Mueller L, Hayden KM, Huang AR, Knopman D, Mitchell CM, Mosley T, Pankow JS, Reed NS, Sanchez V, Schrack JA, Windham BG, Coresh J; ACHIEVE Collaborative Research Group. Hearing intervention versus health education control to reduce cognitive decline in older adults with hearing loss in the USA (ACHIEVE): a multicentre, randomised controlled trial. Lancet. 2023;402(10404):786-797. doi:10.1016/S0140-6736(23)01406-X

Your fasting glucose was normal at your last check-up. Your doctor didn’t flag anything. You have no diagnosis. Here’s what that result probably missed.

Insulin resistance — the impaired ability of cells to respond to insulin’s signal to absorb glucose — doesn’t announce itself. It develops gradually, over years. And crucially, it develops long before fasting glucose becomes abnormal.

A landmark prospective analysis of 6,538 adults followed for nearly a decade found that markedly reduced insulin sensitivity was detectable more than 10 years before a diabetes diagnosis was made, during which time fasting glucose remained in the normal range throughout.¹

That number is worth sitting with. A decade of a process building, tissues adapting, metabolic function shifting, with a standard annual blood test showing nothing of note.

Most people find out they have a problem when it has already progressed past the point where intervention is easiest. This post is about finding out before that.

Subscribe now

How Insulin Resistance Develops

Insulin’s primary job is to signal cells — mainly in skeletal muscle, the liver, and fat tissue — to absorb glucose from the bloodstream after a meal. It does this by binding to insulin receptors on cell surfaces, triggering a cascade that moves glucose transporters (specifically a protein called GLUT4, or glucose transporter type 4) from inside the cell to the cell membrane. Once at the membrane, GLUT4 lets glucose in.

In insulin resistance, this process is impaired. The insulin signal arrives, but the cellular response is blunted. GLUT4 doesn’t move efficiently. Glucose stays in the bloodstream longer. The pancreas detects this and responds by producing more insulin — compensating for the weak signal by turning up the volume.² This is compensatory hyperinsulinemia, and it’s the first stage of insulin resistance. At this point, blood glucose is still entirely normal. Fasting glucose is fine. Only fasting insulin would reveal what’s happening.

Over years, the compensation continues. The pancreas works harder and harder to maintain normal glucose levels. Fasting insulin climbs. HOMA-IR (Homeostasis Model Assessment of Insulin Resistance — a calculated index using fasting insulin and fasting glucose) rises. Eventually, the pancreas can’t fully compensate. Fasting glucose begins to creep up. The person enters the prediabetes range. Without intervention, this progresses to type 2 diabetes — the point at which the pancreatic beta cells that produce insulin have been so chronically overworked that their capacity is permanently reduced.²

The progression is a spectrum. And at every stage before end-stage beta cell failure, it’s reversible.

Share

Why Insulin Resistance Matters Well Beyond Diabetes

Insulin resistance is often framed as a diabetes precursor. That framing understates it considerably.

Insulin resistance is the upstream driver of most of the chronic diseases that shorten and diminish adult life. Cardiovascular disease. Metabolic dysfunction-associated steatotic liver disease — the condition formerly called non-alcoholic fatty liver disease, now the most common liver disease globally. Cognitive decline and Alzheimer’s disease, in which impaired insulin signaling in the brain is now recognized as so central that some researchers describe it as “type 3 diabetes.” Polycystic ovary syndrome (PCOS). Several cancers, including colorectal, pancreatic, and endometrial, for which insulin and insulin-like growth factor signaling are established tumor-promoting pathways.

None of these conditions are caused solely by insulin resistance. All of them are substantially driven by it. And in the majority of adults who develop them, insulin resistance has been present for years before the diagnosis.

This is why the question of where you sit on the insulin resistance spectrum is one of the most clinically important questions in preventive medicine. And it’s one that most standard check-ups don’t answer.

In the rest of this post, we’ll make that question practical. We’ll go through the insulin resistance spectrum — from optimal insulin sensitivity to prediabetes — and the markers that help distinguish early compensation from meaningful metabolic dysfunction. We’ll cover the tests that can detect insulin resistance before fasting glucose changes, the symptom patterns people often dismiss as “normal aging” or “just being tired,” and the evidence-backed interventions that most consistently improve insulin sensitivity. By the end, you’ll know what to look for, what to ask for, and which levers actually move the needle.

I’ve put together a downloadable assessment — a scored tool covering the symptoms, risk factors, and lifestyle inputs that together indicate where someone is likely to sit on the spectrum. It includes the specific tests to request, what the numbers mean, and what scores to aim for. Paid subscribers will find it at the end of the post.

Read more

The death doesn’t come from the fracture itself, it comes from pneumonia from immobility, blood clots from prolonged bed rest, cardiac events from the surgical stress, and a functional decline that many older adults never recover from.

One in three women and one in five men over 50 will sustain at least one osteoporotic fracture in their remaining lifetime — hip, spine, forearm, or wrist.¹ The spine fractures that cause height loss and chronic back pain are often discovered incidentally on a routine X-ray, long after they occurred. The disease has no symptoms. No pain during the years of bone loss. No warning. Just a fracture.

This is preventable. But not with a calcium tablet, and not at 65. It requires a specific set of interventions, most of which carry strong clinical evidence, most of which need to start earlier than current guidelines suggest, and most of which your doctor probably hasn’t raised.

Subscribe now

Why the Standard Screening Window Is Too Late

The official DEXA scan recommendation for average-risk adults is age 65 for women and 70 for men. DEXA (dual-energy X-ray absorptiometry) is the imaging test that measures bone density — it’s when bone density is first measured, and when the osteoporosis conversation typically starts.

Bone loss starts 15 to 20 years earlier.

Peak bone mass is reached by around age 30. After 40, bone formation begins to fall behind resorption in both sexes, though the rate differs. In women, the hormonal shift of the menopausal transition triggers a period of rapid loss: bone mineral density at the lumbar spine drops approximately 1.8 to 2.3% per year in late perimenopause, with cumulative losses of 6% or more across the 5-year transition.³

In men, loss is slower but continuous: roughly 0.5 to 1.0% per year from midlife, accelerating with declining testosterone after 70. By 65, most adults have lost a substantial fraction of their peak bone mass regardless of sex.

A DEXA at 65 or 70 measures what’s left after 15 to 20 years of that loss. It gives a single number with no baseline to compare against. Two people can have the same T-score while one has lost 8% of their peak density and the other has lost 25%. The scan can’t tell them apart. The trajectory — the only number that tells you where things are heading — was never recorded.

Guidelines haven’t caught up to this.

Share

Six Interventions With Clinical Trial Evidence

The paid section covers six interventions with specific clinical trial evidence, including the precise parameters that produce the documented effects. Five of the six require no prescription. All six work best when started before bone density has dropped far enough that fracture risk becomes the primary concern.

I’ve also put together a downloadable bone health assessment — a tool that covers your personal risk factors, scores your current lifestyle across all six intervention areas, and lists the specific tests to request and questions to ask at your next appointment. It’s designed to be printed and taken to your doctor. Paid subscribers will find it at the end of the post.

Read more

Approximately 43% of daily actions are not decisions. They’re automatic repetitions, behaviors triggered by context cues and run by the basal ganglia without conscious involvement.¹

Nearly half. Think about what that means for a day. The phone that’s already in your hand before you have consciously chosen to reach for it, the snack that’s half eaten before you noticed you were hungry, the evening on the couch that begins before a conscious decision to sit down has been made… They were the output of a system running programs it built through repetition, and the only way to change the output is to change the system, not to try harder within it.

A landmark experience-sampling study documented this precisely, tracking participants’ behavior, thoughts, and emotions in real time across multiple days through hourly self-reports.¹ The researchers found that habitual behaviors — performed repeatedly in stable contexts, were executed without corresponding conscious thought. Participants’ minds were elsewhere. The behavior ran without them.

This is the system you’re trying to change when you decide to build a new health habit.

Subscribe now

Why Willpower Always Loses Eventually

Willpower is a function of the prefrontal cortex — the brain’s deliberate, conscious decision-making center. It’s also a depletable resource. Every decision made, every impulse resisted, every moment of sustained effort draws from the same finite pool. By the end of a demanding day, the prefrontal cortex is running at reduced capacity. This is not a character failing. It’s the predictable output of a system that was never designed to sustain conscious effort indefinitely.

The basal ganglia, by contrast, does not deplete. It runs automatic behavioral sequences from stored contextual associations. Once a behavior becomes sufficiently habitual, it shifts from prefrontal control to basal ganglia control. At that point, the behavior no longer requires willpower because it no longer requires conscious initiation at all.

This is the fundamental asymmetry that most health advice ignores. You’re attempting to build new behaviors using the depletable system — willpower, intention, motivation — while the behaviors you’re trying to replace are running on the non-depletable system — automaticity, context cues, ingrained routine. The contest is not fair. It was never going to be fair. And it explains why most habit change attempts follow an identical arc: strong intention, consistent early effort, mounting friction, eventual collapse back to the default.

The people who successfully sustain health behaviors long-term are not the ones with superior motivation. Research is unambiguous on this point. They’re the ones who have arranged their environment so that the right behavior is the automatic one, so that the basal ganglia, left to run its programs, runs the ones they want.

Share

The Problem With Most Habit Advice

Most of the advice in this space asks you to do more with the system that is already failing you. Set clearer goals. Build stronger motivation. Visualize success. Track your progress. Find accountability. Some of them help at the margins, but they’re all still operating through conscious effort and they’re all still subject to the same depletion that causes the original failure.

The behavioral science literature has identified a different category of tools entirely. They don’t ask you to try harder. They change the conditions under which behavior occurs. They work with the automatic architecture rather than against it, altering the environment, the timing, and the contextual cues so that the behavior you want becomes the one that runs automatically.

There are three of them. Each one has clinical trial evidence behind it. Each one produces measurable improvements in habit formation independent of motivation levels. And used together, they create the structural conditions in which the right behavior becomes the default — not through effort, but through design.

The paid section covers all three in full clinical detail, including the specific research, the exact implementation steps, and the common failure points for each. The downloadable Behavior Change Planning Tool at the end of this post walks you through all three for any habit you choose, and takes about five minutes to complete.

If you’ve tried to build a health habit before and watched it fail despite genuine effort and good intentions, what follows is the part of the explanation you were not given.

Read more

It’s so frustrating when you sleep, you rest, you try to do everything “right,” and you still wake up feeling as if your body never fully recharged.

I know that feeling. During medical school, I went to my doctor because I was deeply exhausted. I expected questions and a proper investigation, but instead, I was told to sleep more. Just that. Sleep more.

This happens all the time. Patients walk into appointments saying, “I’m exhausted, but my labs are normal.” They’re told they’re stressed, busy, aging, anxious, not sleeping enough, or simply doing too much. Okay, sometimes that’s part of the picture, but it’s not the whole picture. Patients deserve better answers than “sleep more.”

Fatigue has at least six distinct metabolic causes, each of which requires a different test, each of which can operate independently of the others, and each of which can be present at clinically meaningful levels while every standard panel comes back within the reference range.

The reference range is the problem. Most laboratory reference ranges are built around population averages, including populations with early, subclinical disease. A result flagged as normal doesn’t mean the level is optimal. It means it falls within the range of the average adult in the sample used to define the reference. For several of the most common causes of fatigue, the gap between “normal” and “optimal” is where many patients are spending their lives.

Share

What the Research Shows

A study published in JAMA Network Open analyzing over 400,000 ferritin tests in primary care settings found that fatigue was the single strongest clinical predictor of ferritin testing, associated with more than double the rate of testing compared to the general clinical population.¹

In other words: fatigue is one of the main reasons people seek answers about iron. Yet the ferritin thresholds most laboratories use to flag deficiency are set so low that a significant proportion of clinically iron-deficient adults are classified as normal.

This is one example of a pattern that repeats across six distinct metabolic pathways. Each pathway has its own mechanism, its own test, and its own gap between what the reference range flags and what the clinical evidence supports. The paid section covers all six — with the specific tests, the specific thresholds that matter, and the exact questions to ask at your next appointment.

A downloadable lab checklist is at the end of this post. It’s designed to be printed and brought to your doctor, and it covers every test mentioned below with the specific language to use and the thresholds to request.

Read more

The advice most people receive about blood sugar has been shaped by assumptions that made clinical sense at the time they were formed. Some of those assumptions have since been tested in large, rigorous studies. Some of them did not survive.

This post covers four of the most consequential ones, the beliefs that most directly influence what people eat and how they interpret their own health data. Each one has been contradicted by peer-reviewed evidence. Each one still circulates widely in clinical settings and popular nutrition advice.

Subscribe now

Myth 1: Fruit Is Bad for Your Blood Sugar

The reasoning sounds logical: fruit contains sugar, sugar raises blood glucose, therefore people managing blood sugar should limit or avoid fruit. This reasoning is wrong — and it’s wrong in a specific, clinically important way.

A landmark study published in the BMJ examined data from 187,382 participants across three long-running Harvard cohort studies, tracking their fruit consumption and the incidence of type 2 diabetes over more than two decades.¹ The finding was direct: people who consumed at least two servings per week of certain whole fruits — particularly blueberries, grapes, and apples — had up to a 23% lower risk of developing type 2 diabetes compared to those who ate them infrequently.

The same study found the opposite for fruit juice: consuming one or more servings per day of fruit juice was associated with a significantly higher risk of type 2 diabetes.

The distinction between whole fruit and fruit juice is the entire story.

When fruit is consumed whole, the fiber matrix slows the digestion and absorption of the sugars it contains. The glucose enters the bloodstream gradually. Insulin response is moderate and controlled. When that same fruit is juiced, the fiber is removed, and the sugar enters the bloodstream rapidly, producing a substantially larger and faster glucose spike, and a correspondingly larger insulin demand.

The food is the same. The fiber changes everything.

The practical implication is precise: whole fruit, eaten as whole fruit, is not a blood sugar problem, for most people in most circumstances. Fruit juice, smoothies where the fiber has been separated out, and dried fruit consumed in quantity are different conversations.

Myth 2: Artificial Sweeteners Are a Safe Blood Sugar Swap

The premise behind artificial sweeteners is simple: they provide sweetness without calories or carbohydrates, so they do not raise blood glucose and are therefore safe — or even beneficial — for people managing blood sugar. For decades this was the default clinical position.

A randomized controlled trial published in Cell in 2022 complicated that position substantially.² The study enrolled 120 healthy adults and divided them into groups that consumed saccharin, sucralose, aspartame, stevia, or no sweetener for two weeks, all at doses below the acceptable daily intake established by regulatory agencies.

Saccharin and sucralose significantly impaired glycemic responses. The other two — aspartame and stevia — did not.

Critically, the researchers established that the effect was mediated by the gut microbiome. The sweeteners altered microbial composition and function, and the resulting microbial changes drove the changes in glucose tolerance. When gut microbiome samples from affected participants were transferred to germ-free mice, the mice showed the same glycemic impairment, confirming that the gut bacteria were the causal link.²

Several things about this finding are worth noting precisely.

1. Not all sweeteners produced the same effect. The evidence specifically implicates saccharin and sucralose — the two most widely used artificial sweeteners in commercial food production. Stevia and aspartame did not produce the same glycemic impairment in this trial.

2. The effect was person-specific, meaning individual microbiome composition determined how large the response was.

3. This was a two-week trial in healthy adults, and the long-term effects of chronic exposure are still being studied.

What this evidence doesn’t support is the assumption that all non-caloric sweeteners are biologically inert. What it specifically supports is a more precise question: which sweetener, for which person, over what duration, and measured by which outcome. Saccharin and sucralose, at minimum, warrant more caution than their widespread use in “sugar-free” products currently reflects.

Share

Myth 3: The Glycemic Index Tells You How Your Body Will Respond

The glycemic index (GI) ranks foods by the speed and magnitude of the blood glucose rise they produce — in the average person, under standardized test conditions. It has shaped decades of dietary advice for people managing blood sugar: choose low-GI foods, avoid high-GI foods, and your glucose will be better controlled.

The problem with this framework is the assumption embedded in “the average person.”

A study published in Cell in 2015 used continuous glucose monitors to track the postprandial blood glucose responses of 800 people to the same foods over an extended period.³ The finding was striking: the same food produced radically different glycemic responses across individuals. A banana that produced a minimal glucose spike in one person produced a substantial spike in another. Brown rice that was glycemically neutral for one person was glycemically disruptive for another. In several cases, the individual responses were so variable that the food rankings reversed entirely — a “low-GI” food produced higher glucose spikes in some people than a “high-GI” food.³

The primary predictor of this individual variation was gut microbiome composition — the specific community of bacteria in each person’s gut, which differs substantially between people and substantially determines how carbohydrates are processed.³

This doesn’t make the glycemic index useless. It’s a useful population-level tool and a reasonable starting point for general dietary guidance, but it’s not a reliable predictor of how a specific food will affect a specific person’s glucose. The response to the same meal is shaped by gut microbiome composition, baseline metabolic status, genetics, body weight, and age — none of which are captured by a food-based index that was derived from population averages.³

The implication for anyone using GI tables as their primary decision-making tool is that they may be optimizing against a metric that does not accurately describe their own body’s response. Continuous glucose monitoring — increasingly accessible through consumer devices — is the only tool that directly measures actual individual glycemic response rather than inferring it from population averages.

Subscribe now

Myth 4: If Your Fasting Glucose Is Normal, Your Blood Sugar Is Fine

Fasting glucose is the measurement most standard blood panels use to assess blood sugar status.

• Below 100 mg/dL is classified as normal.

• Between 100 and 125 mg/dL is prediabetes.

• Above 126 mg/dL on two separate readings is diabetes.

The clinical problem: fasting glucose is a late marker.

Insulin resistance — the state in which cells become less responsive to insulin’s signal to absorb glucose from the bloodstream — develops gradually over years, sometimes more than a decade before diagnosis.

A prospective analysis of 6,538 civil servants followed for nearly 10 years found that markedly reduced insulin sensitivity was detectable more than 10 years before a diabetes diagnosis was made, during which time fasting glucose remained in the normal range.⁴ During this period, the pancreas compensates for the reduced cellular response by producing more insulin. Blood glucose stays in the normal range because the pancreas is working harder to keep it there.

The earlier marker of insulin resistance is fasting insulin — and the calculated ratio of fasting insulin to fasting glucose known as HOMA-IR. A person with a fasting glucose of 92 mg/dL (normal) and a fasting insulin of 16 mIU/L (often not flagged by standard laboratory ranges) has a HOMA-IR of approximately 3.6 — clearly in the insulin resistance range, with meaningful cardiovascular and metabolic risk implications that the glucose number alone is concealing.

The American Diabetes Association’s own Standards of Care now explicitly state that prediabetes represents a significant risk factor for cardiovascular disease independent of diabetes progression — meaning the risk of harm begins before the glucose threshold for prediabetes is crossed, and accumulates across the entire glucose range below that threshold.⁵

The practical implication: a normal fasting glucose result is worth knowing, but it’s not sufficient on its own to conclude that blood sugar regulation is healthy. Fasting insulin, calculated alongside fasting glucose as HOMA-IR, provides the earlier signal, often years before fasting glucose moves.

Share

What This Adds Up To

None of these findings have fully reached standard clinical practice. Most people receiving blood sugar advice from their GP are still operating within the original framework.

The common thread across all four myths is the gap between the population-level heuristic and what actually happens in an individual body. Whole fruit is protective on average, but your response depends on the fiber remaining intact. Artificial sweeteners vary by type and by your microbiome. The glycemic index describes average responses to foods, not your responses. Fasting glucose describes a threshold that is crossed years after the underlying dysfunction begins.

Blood sugar regulation is more individual, more dynamic, and detectable earlier than the standard framework acknowledges.

Leave a comment

To your zenith within,

Sara Redondo, MD, MS

References:

1. Muraki I, Imamura F, Manson JE, Hu FB, Willett WC, van Dam RM, Sun Q. Fruit consumption and risk of type 2 diabetes: results from three prospective longitudinal cohort studies. BMJ. 2013;347:f5001. doi:10.1136/bmj.f5001

2. Suez J, Cohen Y, Valdés-Mas R, Mor U, Dori-Bachash M, Federici S, et al. Personalized microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance. Cell. 2022;185(18):3307-3328.e19. doi:10.1016/j.cell.2022.07.016

3. Zeevi D, Korem T, Zmora N, Israeli D, Rothschild D, Weinberger A, et al. Personalized nutrition by prediction of glycemic responses. Cell. 2015;163(5):1079-1094. doi:10.1016/j.cell.2015.11.001

4. Tabák AG, Jokela M, Akbaraly TN, Brunner EJ, Kivimäki M, Witte DR. Trajectories of glycaemia, insulin sensitivity, and insulin secretion before diagnosis of type 2 diabetes: an analysis from the Whitehall II study. Lancet. 2009;373(9682):2215-2221. doi:10.1016/S0140-6736(09)60619-X

5. American Diabetes Association Professional Practice Committee. Diagnosis and classification of diabetes: Standards of Care in Diabetes — 2026. Diabetes Care. 2026;49(Suppl 1):S27-S49. doi:10.2337/dc26-S002

There’s a maintenance process your mitochondria depend on that declines with age more profoundly than almost any other quality control system in the body.

It’s called mitophagy.

Mitochondria are continuously damaged by the reactive oxygen species generated during their own energy production, by environmental stressors, and by the simple wear of function over time. The cellular response to this damage is mitophagy — a selective process in which the cell identifies damaged mitochondria, tags them for removal, and degrades them in a controlled way. What follows the clearance is mitochondrial biogenesis: the production of new, functional mitochondria to replace those removed.

This cycle — damage, clearance, regeneration — is what keeps the mitochondrial population functional. When it works well, the cell maintains a population of high-performing mitochondria capable of meeting its energy demands. When it fails, damaged mitochondria accumulate. Energy production becomes inefficient. The downstream effects touch every tissue in the body: skeletal muscle loses force-generating capacity, immune cells become less responsive, the brain’s metabolic support deteriorates, and the biological aging process accelerates measurably.

Mitophagy declines with age. Specifically, the molecular pathway that initiates it — PINK1/Parkin-mediated mitophagy — shows progressive functional impairment starting in midlife. This is one of the most mechanistically well-supported explanations for why mitochondrial function declines with age even in people who exercise, sleep well, and eat a healthy diet. The maintenance system itself is failing.

What researchers at the École Polytechnique Fédérale de Lausanne and the Swiss longevity biotech Amazentis established over a decade of research is that a specific molecule induces mitophagy more potently than any other naturally occurring compound identified in human research to date — and that in the right dose, it’s safe, bioavailable, and produces measurable improvements in mitochondrial function in humans.¹

That molecule is Urolithin A.

Subscribe now

What Urolithin A Is and Where It Comes From

Urolithin A is not a plant chemical you consume directly. It’s a postbiotic — a compound your gut bacteria produce by metabolizing plant chemicals called ellagitannins. The conversion pathway works like this: ellagitannins in food are hydrolyzed in the stomach into ellagic acid, which then passes into the colon where specific gut bacteria — primarily Akkermansia muciniphila and certain Clostridia species — convert ellagic acid through a series of steps into Urolithin A.

The foods that contain meaningful concentrations of ellagitannins: pomegranate (the richest dietary source), walnuts, raspberries, blackberries, strawberries, and muscadine grapes. Pomegranate juice is commonly cited as the primary dietary source, and pomegranate extracts have been used as the reference food in the clinical research on Urolithin A production.

Here’s the problem that most content about Urolithin A ignores.

In a study of 100 healthy adults given pomegranate juice to test their Urolithin A producer status, only approximately 40% of participants showed significant conversion of ellagitannins to Urolithin A.² The remaining 60% produced either trace amounts or none at all — not because they ate less pomegranate, but because their gut microbiome did not contain the bacteria required for the conversion.²

Three human metabotypes have been characterized:

1. UM-A (efficient producers of Urolithin A)

2. UM-B (producers of less active urolithin metabolites)

3. UM-0 (non-producers)

Metabotype is largely determined by gut microbiome composition and doesn’t reliably respond to dietary changes in short-term interventions.²

Even among the 40% who were classified as producers, pomegranate juice produced plasma Urolithin A levels that were six times lower than direct supplementation with 500mg of Urolithin A.² Eating pomegranate regularly may provide some Urolithin A for people with the right microbiome, but it doesn’t reliably achieve the concentrations that the clinical research was conducted at.

This is why the clinical evidence for Urolithin A is based entirely on direct supplementation — and why the dietary framing in most coverage of this compound is clinically misleading.

Share

Before You Buy Anything, Read This

The clinical trial evidence for Urolithin A now spans four separate human trials, published in Nature Metabolism, Cell Reports Medicine, JAMA Network Open, and Nature Aging. The outcomes range from mitochondrial gene expression and biomarkers of cellular health to muscle strength, endurance, exercise capacity, and immune cell function. The dose used across the trials, the duration required to see meaningful effects, and the distinction between the proprietary pharmaceutical-grade form tested in trials and generic supplements available commercially are all clinically relevant and are covered below.

Read more

For decades, the conversation about exercise and longevity has been dominated by aerobic fitness. Cardiovascular training has the oldest and deepest evidence base, and it deserved the attention it received.

What has been consistently underrepresented in that conversation is resistance training. Not because the evidence was absent, but because the studies were smaller, shorter, and harder to compare. Until now.

A study published this week in the British Journal of Sports Medicine followed 147,374 adults across three Harvard cohorts for up to 30 years, tracking weekly resistance training volume every two years and mapping it against mortality outcomes across multiple causes of death. It’s the largest and longest study ever conducted on the dose-response relationship between strength training and longevity.¹

The lead finding is a specific number: 90 to 120 minutes of resistance training per week.

What the Study Found

Adults who averaged 90 to 119 minutes of weekly resistance training had a 13% lower risk of death from any cause compared to those who did none — after adjusting for age, lifestyle, and health status.¹

That same weekly amount was associated with a 19% lower risk of death from cardiovascular disease and a 27% lower risk of death from neurological disease, including Alzheimer’s.

The cancer mortality findings were distinct and worth noting separately: the relationship between resistance training and cancer mortality was less dose-dependent. Even very small amounts — as little as 1 to 29 minutes per week — were associated with a 21% lower cancer mortality risk. 30 to 59 minutes per week produced an 18% reduction. The benefits didn’t continue to grow proportionally with more training the way they did for cardiovascular and neurological outcomes.

Two additional findings define the shape of the evidence:

1. More training above 120 minutes per week produced no additional benefit. The mortality risk curve flattened completely above that threshold. This is not a reason to stop at 120 minutes if you enjoy more, it simply means that for the longevity benefit, additional time above this amount doesn’t add a measurable survival advantage.

2. Combining resistance training with aerobic exercise produced the largest effects of all. Participants who did both high aerobic activity and 60 to 119 minutes per week of strength training had up to a 45% lower all-cause mortality risk than those who did neither. Resistance training and aerobic training are not competing priorities. They are complementary ones, and the data on what they produce together is extraordinary.

Subscribe now

The Gap This Study Does Not Fill

This is a landmark observational study. It establishes what the dose-response relationship looks like between resistance training volume and mortality, information that didn’t exist at this scale and duration before this paper was published.

What it doesn’t tell us is which exercises produce the adaptation that lowers our mortality risk — and which ones, despite filling the time, do not. It doesn’t tell us how heavy to lift, or why the answer to that question changed significantly with guidelines published just weeks ago. It doesn’t tell us the protein threshold that determines whether our training produces muscle adaptation at all — a threshold most people over 50 are not hitting at any single meal. It doesn’t tell us how to sequence strength and aerobic training in the same week without undermining either. And it says nothing about what women specifically need to do differently — particularly in perimenopause, when the stakes for getting this right are at their highest and the standard advice is at its most generic.

That’s what the paid section covers.

Read more

I wrote about mitochondria recently — why they decline with age, what that decline means for your energy, your metabolism, and your disease risk, and what the evidence supports for protecting them.

This week, a paper in Nature Communications added a new chapter to that story. And because this finding connects directly to a nutrient most people have never thought about in this context, it’s worth covering immediately.

Subscribe now

What the Study Found

Researchers at the Leibniz Institute on Aging in Jena, Germany, set out to answer a question that has puzzled cell biologists for decades:

Their answer, published on April 18, 2026, points to a membrane lipid called phosphatidylcholine.

Phosphatidylcholine is the most abundant phospholipid in biological membranes — it makes up roughly 40-50% of the lipid bilayer of every cell membrane in your body. Its primary structural role is maintaining membrane fluidity and flexibility: the capacity of a membrane to reorganize, bend, and respond to changing conditions.

That flexibility turns out to be essential for a process called mitochondrial fusion — one of the most important maintenance mechanisms in the cell.

Mitochondria are not static structures. They constantly move, divide, and, critically, fuse together into interconnected networks. When mitochondria fuse, they share components: energy molecules, metabolic enzymes, and mitochondrial DNA. This sharing allows damaged parts to be diluted, functional parts to be distributed, and the mitochondrial population as a whole to maintain its quality.

A connected mitochondrial network is a resilient one.

When phosphatidylcholine levels fall, membranes lose the flexibility required for fusion. Mitochondria fragment into isolated units that cannot share resources or repair themselves effectively. Energy production becomes inefficient. Metabolic plasticity — the cell’s ability to adapt to changing energy demands — declines. This fragmented pattern is one of the consistent microscopic signatures of aging cells.

Share

The Experiment — and the Honest Limits

The research team found that phosphatidylcholine production decreases naturally with age in C. elegans — the roundworm that is one of the most studied model organisms in aging research.

When they switched off the genes responsible for producing phosphatidylcholine in young worms, those worms rapidly developed mitochondrial characteristics typical of much older organisms. When they supplemented aging worms with phosphatidylcholine, mitochondrial function partially recovered to more youthful patterns.

To check whether the finding might apply to humans, the team analyzed existing data from human aging studies. They found the same decline in phosphatidylcholine production pathways — suggesting that what happens in worms also happens in us.

Here is what the evidence does and does not say.

• It does say: phosphatidylcholine decline is a significant, previously underappreciated contributor to the mitochondrial dysfunction that characterizes aging in worms, with supporting evidence that the same pathway declines in humans.

• It does not say: supplementing phosphatidylcholine in humans will reverse mitochondrial aging. No human supplementation trial was conducted. The researchers themselves noted that phosphatidylcholine is found in many commonly eaten foods and that the doses required for a clinically meaningful effect are not yet established. Their own conclusion: “it seems unlikely that we have deficiencies that require supplements, unless the necessary dosage is extremely high.”

This distinction matters. The finding is mechanistically important. It identifies a specific, targetable molecular event in the mitochondrial aging process. It opens a research direction. It does not, yet, constitute evidence for a supplement recommendation.

What It Adds to the Mitochondria Picture

The significance of this paper is not that it tells us to take a phosphatidylcholine supplement. It’s that it identifies the specific mechanism by which one aspect of mitochondrial aging occurs, and establishes that this mechanism is malleable, meaning it can be influenced.

The mitochondria post covered why declining mitochondrial function accelerates aging across every major system in the body. This paper adds something new: a specific molecular mechanism — identified after that post was published — that explains one of the key ways healthy mitochondria deteriorate with age.

This paper offers one clear answer: the lipid environment of the mitochondrial membrane. As phosphatidylcholine levels fall, the physical properties of the membrane change in ways that impair the fusion machinery on which mitochondrial network maintenance depends. This is the trigger before the consequence.

The implication is that dietary factors influencing phosphatidylcholine status may matter more to mitochondrial health than previously appreciated — not as a supplement, but as an aspect of nutritional adequacy that most people, and most dietary guidance, do not explicitly address.

Subscribe now

The Dietary Connection

Phosphatidylcholine is found in food, and the richest sources are not particularly exotic:

• Eggs — particularly egg yolks — are the most concentrated dietary source of choline (which the liver uses to synthesize phosphatidylcholine). One large egg yolk provides approximately 150mg of choline. The adequate intake for choline in adults is 425mg/day for women and 550mg/day for men.

• Liver — beef and chicken liver contain the highest absolute concentrations of dietary phosphatidylcholine. Three ounces of beef liver provides approximately 420mg of choline — close to the full daily adequate intake in a single serving.

• Fish, particularly salmon and cod — meaningful sources.

• Soybeans and sunflower lecithin — the primary plant sources. Lecithin, found widely as a food additive and supplement, is largely composed of phosphatidylcholine.

There is a meaningful difference between being deficient in a nutrient and getting enough of it to support optimal function. Most adults globally are not severely choline-deficient, but most are also not consuming enough to reliably meet the daily recommended targets that support phosphatidylcholine synthesis.

In the United States, fewer than 1 in 10 adults reaches the recommended intake. In Europe, the picture is similar.

Share

This is not a reason to start a supplement. It’s a reason to take the choline content of your diet more seriously than most nutritional conversations do, and to stop discarding egg yolks.

The Broader Pattern

What this paper is part of is a research direction that is becoming one of the most productive in aging biology: the identification of specific, reversible molecular events upstream of the mitochondrial dysfunction that accelerates aging.

Phosphatidylcholine synthesis is now one of those identified upstream events. So is NAD+ depletion, covered in the mitochondria post. So are the senescent cell dynamics covered in the zombie cell post. So is the epigenetic drift now measurable through aging clocks.

What the research increasingly shows is that aging is not a single unstoppable process. It is several distinct mechanisms running in parallel, each of which appears to be individually modifiable.

This paper is a piece of that larger picture. Not the whole story, but an important new chapter. See you in next one.

Leave a comment

To your zenith within,

Sara Redondo, MD, MS

Resources:

Poliezhaieva T, Li Y, Chaudhari PS, Isildak U, Alonso-Pernas P, Valentim IS, Su F, Espada L, Bayar M, Fu L, Koeberle A, Dönertaş HM, Ermolaeva MA. Aging-associated decline of phosphatidylcholine synthesis is a malleable trigger of natural mitochondrial aging. Nat Commun. 2026;17(1):3589. doi:10.1038/s41467-026-71508-7

Zuk E, Nikrandt G, Chmurzynska A. Dietary choline intake in European and non-European populations: current status and future trends — a narrative review. Nutr J. 2024;23(1):68. doi:10.1186/s12937-024-00970-0

Every time you eat a protein, your body extracts an amino acid called tryptophan. Tryptophan has one job that most people know about: it’s the raw material from which the brain synthesizes serotonin.

But tryptophan faces a fork in the road before it gets there.

One fork leads to 5-hydroxytryptophan, then to serotonin — the neurotransmitter involved in mood, emotional regulation, and sleep. The other fork leads to the kynurenine pathway — a metabolic route that produces, among other things, quinolinic acid, a neuroexcitatory compound associated with neuroinflammation, hippocampal damage, and the kind of treatment-resistant depression that does not respond to antidepressants that target serotonin.

Which fork tryptophan takes is substantially determined by inflammation. And one of the primary drivers of systemic inflammation is the state of your gut microbiome.

When gut bacteria are diverse and well-balanced, they produce short-chain fatty acids, regulate the intestinal barrier, and suppress the pro-inflammatory signaling that activates the enzyme — indoleamine 2,3-dioxygenase, or IDO — that diverts tryptophan away from serotonin and toward kynurenine. When gut bacteria are dysregulated, IDO activity rises, tryptophan is increasingly routed toward neurotoxic metabolites, and the brain’s capacity to synthesize serotonin is reduced at the level of raw material, before the brain has done anything wrong.

This is one of four distinct biological pathways through which the gut microbiome influences brain function. None of them require serotonin to travel from the gut to the brain — peripheral serotonin, produced in the gut for the purpose of regulating intestinal motility, does not cross the blood-brain barrier. The brain makes its own serotonin, from tryptophan that the gut microbiome’s inflammatory state helps determine the availability of.

Your doctor has almost certainly assessed none of these pathways.

Subscribe now

The Four Pathways — How the Gut Actually Talks to the Brain

Understanding the mechanisms matters, because it explains why gut-targeted interventions produce measurable brain effects, and why the interventions that work for the microbiome are the same ones that consistently appear in the mood and cognition literature.

Pathway 1: Tryptophan-kynurenine balance. Gut dysbiosis drives systemic and intestinal inflammation, which activates IDO, which diverts dietary tryptophan away from the brain serotonin synthesis pathway. Certain gut bacteria — particularly Lactobacillus and Bifidobacterium species — regulate this directly by maintaining the intestinal environment that keeps IDO activity low. When these bacteria are depleted, IDO activity rises and the tryptophan-to-serotonin conversion rate falls.¹

Pathway 2: Short-chain fatty acids. When gut bacteria ferment dietary fiber, they produce short-chain fatty acids — primarily butyrate, propionate, and acetate. Butyrate in particular crosses the blood-brain barrier. Inside the brain, it promotes BDNF (brain-derived neurotrophic factor, the growth factor that maintains neuronal health and is suppressed in depression), reduces microglial-driven neuroinflammation, modulates the HPA stress axis, and supports blood-brain barrier integrity. Butyrate-producing bacteria — particularly Faecalibacterium prausnitzii — are among the most consistently depleted organisms in the microbiomes of people with depression and anxiety.¹

Pathway 3: Vagal nerve signaling. The vagus nerve, the primary anatomical cable of the gut-brain axis, carries electrochemical signals from the intestinal wall directly to the brainstem, and from there into the limbic system, where emotional regulation occurs. Specific gut bacteria activate vagal afferent neurons through direct receptor engagement. GABA-producing bacteria, including Lactobacillus rhamnosus, influence vagal tone in ways that reduce anxiety-like behavior in animal models and are under active investigation in human trials.¹

Pathway 4: Intestinal permeability and neuroinflammation. A healthy gut epithelium is a selective barrier. In gut dysbiosis, tight junction proteins become dysregulated, increasing intestinal permeability. Lipopolysaccharides — the endotoxins from the outer membrane of gram-negative bacteria — cross into the bloodstream. They activate toll-like receptor 4 on immune cells throughout the body, triggering the production of IL-1β, IL-6, and TNF-alpha at concentrations that cross the blood-brain barrier and directly impair hippocampal neurogenesis, serotonin synthesis, and BDNF expression. This is the metabolic endotoxemia pathway, and it’s one of the most compelling bridges between gut dysbiosis and the neuroinflammatory hypothesis of depression.¹

Share

What Dysbiosis Looks Like in Depression and Anxiety

Studies using 16S rRNA sequencing and metagenomic analysis have identified consistent microbial signatures in people with depression and anxiety compared to healthy controls.¹

In major depressive disorder, the most consistently replicated findings are:

• Reduced overall microbial diversity; depletion of Faecalibacterium prausnitzii — the primary butyrate producer whose absence disrupts pathway 2 above.

• Depletion of Coprococcus and Blautia — additional SCFA-producing genera associated with positive mental health.

• Enrichment of pro-inflammatory species including Eggerthella, Flavonifractor, and Holdemania, which are associated with increased intestinal permeability and LPS production.

In anxiety, the signature includes depleted SCFA-producing bacteria and elevated Proteobacteria — a phylum associated with gut inflammation and impaired barrier function.¹

These findings are mechanistically coherent. The depleted bacteria are precisely the ones that produce anti-inflammatory metabolites, maintain the intestinal barrier, and regulate the tryptophan pathway. The enriched bacteria are the ones whose products drive systemic inflammation and intestinal permeability. Dysbiosis is the signature of a system whose anti-inflammatory and neuroprotective output has been systematically eroded.

Subscribe now

What the Evidence Supports — and What It Does Not Yet Prove

Causality has not been definitively established. The studies identifying dysbiosis in depression are largely cross-sectional — depression and gut dysbiosis co-occur, but the direction of causation is not proven in humans. Depression itself alters diet, sleep, stress hormones, and medication — all of which reshape the microbiome. The relationship is bidirectional, and that bidirectionality makes clean causal inference difficult.

Germ-free animal studies, in which transplanting microbiomes from depressed humans into mice produces depressive-like behavior, are suggestive of causality but cannot be directly translated to humans.

What randomized controlled trials do establish — a higher bar than mechanistic and observational data — is that gut-targeted interventions produce measurable changes in depression and anxiety symptoms in clinically diagnosed populations. The mechanism is not fully characterized, but the clinical effect is documented.

The paid section covers what those interventions are, what the trial evidence shows specifically, and the distinctions that separate what works from what is marketed.

Read more

The global collagen market exceeded $9 billion in 2025 and is still growing.

We see collagen everywhere. In the powder next to the coffee machine, in the peptides dissolved into your friend’s morning smoothie, in the gummies, the capsules, the beauty drinks, the joint support supplements, the protein powders that now add it to the label…

For years, the clinical answer to “does it work?” has been: we don’t really know. The existing studies were mostly small, mostly short, often funded by the companies selling the product, and spread across different outcomes with different doses and different measurement tools. Meta-analyses existed but covered narrow slices of the evidence. The field needed a synthesis large enough to give a clear answer.

That synthesis was published this week.

Researchers at Anglia Ruskin University combined data from 16 systematic reviews, 113 randomized controlled trials, and 7,983 participants from around the world — the most comprehensive evidence review on collagen supplementation ever conducted.

For the first time, we have enough data to say clearly: here is what collagen does, here is what it does not do, and here is what it takes to see results.

Subscribe now

First: Why Collagen Declines — and Why That Matters

Collagen is the most abundant protein in the human body. It’s the structural scaffold of the skin, the cartilage that cushions joints, the framework of tendons and ligaments, and a major component of bone. It gives skin its firmness and elasticity, and it’s the matrix that keeps joint surfaces smooth and mobile.

The body produces its own collagen continuously, and around age 25, production begins declining at approximately 1-1.5% per year. By the time most people are in their 40s, the cumulative loss is measurable: skin loses elasticity and firmness, joints become more vulnerable to wear, and recovery from mechanical stress slows.

This decline is accelerated by several modifiable factors:

• UV exposure directly degrades collagen in the dermis through oxidative damage.

• Smoking triggers enzymes (matrix metalloproteinases) that break down collagen.

• Chronic high sugar consumption causes glycation — glucose molecules binding to collagen fibers, making them stiff and fragile.

• Chronic stress, via cortisol, suppresses fibroblasts — the cells that produce new collagen.

The Mechanism Skeptics Missed

For years, the scientific objection to collagen supplements was straightforward: collagen is a protein. The digestive system breaks proteins into amino acids. There’s nothing special about the amino acids from collagen versus those from chicken breast or eggs — the body cannot direct them specifically toward skin or joints. You might as well eat more protein.

This argument was reasonable given the evidence available at the time. But it’s no longer adequate.

Subsequent research has established that hydrolyzed collagen — the form used in most supplements, also called collagen peptides — produces specific bioactive di- and tripeptides (notably Pro-Hyp and Hyp-Gly) during digestion that survive absorption partially intact and are detectable in the bloodstream. These peptides appear to accumulate preferentially in skin tissue and cartilage, where they have two documented actions:

• They stimulate fibroblasts to increase collagen synthesis.

• They have direct anti-inflammatory effects in joint tissue.

This is why the old objection doesn’t hold. Not all protein produces these specific peptides. The question was whether the effect size, in humans, across real clinical trials, was large enough to matter clinically. That is what the umbrella review answers.

Share

What the Evidence Now Supports

Skin elasticity and hydration — clear, high-certainty evidence.

Collagen supplementation produced statistically significant improvements in both skin elasticity and skin hydration compared to placebo across the included trials, with high statistical confidence.

The effect is duration-dependent: longer supplementation is associated with greater improvement, with meaningful changes beginning to emerge at 8-12 weeks of consistent daily use.

What it does not mean: wrinkles disappear, skin roughness improves, or visible aging reverses dramatically. The review didn’t find significant improvements in skin roughness. The effects are real and meaningful, but they’re incremental improvements in biological skin parameters, not a cosmetic transformation.

Osteoarthritis — consistent and significant symptom relief.

Across the osteoarthritis trials, collagen supplementation was associated with significant reductions in joint pain and stiffness.

The WOMAC score — the Western Ontario and McMaster Universities Arthritis Index, the most widely validated patient-reported outcome measure for osteoarthritis, which assesses pain, stiffness, and physical function on a standardized scale — showed high-certainty improvements in total score and stiffness subscale.

Longer supplementation was again associated with better outcomes. The lead researcher described the benefits as “credible and clinically meaningful.”

The mechanism here is different from skin: in cartilage, collagen peptides appear to reduce the inflammatory signaling that drives osteoarthritic degradation, and may stimulate chondrocytes — the cells that produce cartilage matrix — to increase their output. For a condition with very limited pharmacological options, it represents genuine clinical value.

Muscle health — modest, real, context-dependent.

The review found collagen supplementation was associated with improvements in muscle architecture and modest gains in muscle strength.

The important nuance: this doesn’t apply to sports performance, post-exercise recovery, or delayed onset muscle soreness, where the evidence showed no meaningful benefit. The muscle effect appears most relevant to populations experiencing age-related muscle loss (sarcopenia) rather than athletes looking for a performance edge.

Subscribe now

What the Evidence Does Not Support

This is the part that matters as much as the positive findings because collagen is marketed heavily for things the evidence does not show it does.

1. Post-workout recovery and athletic performance. The umbrella review found no meaningful improvements in post-exercise soreness, recovery time, or tendon mechanical properties. The fitness industry’s collagen marketing has significantly outrun the evidence. If you’re adding collagen to your post-workout routine for recovery, you’re probably wasting money on the wrong thing.

2. Wrinkle elimination or skin roughness. Skin elasticity and hydration improved. Skin roughness didn’t. Collagen supplements are not a topical or injectable treatment and do not produce equivalent results.

3. Cardiometabolic health. The review found mixed results for blood sugar, blood pressure, and cholesterol outcomes. The evidence is insufficient to recommend collagen supplementation for cardiovascular or metabolic health.

4. Oral and dental health. Also mixed results, with not enough evidence either way.

Share

What the Study Could Not Tell Us

The umbrella review itself noted several important limitations worth understanding before you act on its findings.

The included studies did not control for UV exposure, smoking, dietary quality, hydration, sleep, or hormonal status — all of which independently influence collagen metabolism. Two people taking the same collagen supplement with different sun exposure or smoking habits will have very different outcomes. Collagen supplements operate on top of a biological environment you are also shaping through everything else you do.

The studies also didn’t compare collagen types head-to-head — bovine vs. marine vs. chicken vs. eggshell membrane. The evidence is strongest for hydrolyzed collagen peptides (the form in most powder supplements), modest for undenatured type II collagen (a specific form used at much lower doses primarily for joints), and weaker for gelatin and collagen from food sources alone. Marine collagen has theoretical bioavailability advantages due to smaller peptide size, but this has not been conclusively demonstrated to translate into better outcomes in large trials.

The question of optimal dose is also not fully resolved. Most trials used 5-15g daily of hydrolyzed collagen. The meta-regression suggested higher doses and longer duration produce larger effects, but head-to-head dose comparison trials have not been done at sufficient scale to identify a clear threshold.

The Bigger Picture

The most important sentence in the Anglia Ruskin press release was this one:

That is the accurate summary. It’s neither the evangelical “collagen will transform your skin” narrative that supplement marketing promotes, nor the dismissive “it’s just protein, save your money” position that many clinicians have held.

What this study establishes is that collagen supplementation, used consistently at adequate doses over an adequate duration, produces real, measurable improvements in two specific and clinically meaningful domains: skin elasticity and hydration, and osteoarthritis symptoms. For a supplement market as large and as claim-laden as collagen, a verdict this specific and this grounded in evidence is unusually clear.

The cofactor that almost no collagen content mentions: vitamin C is required for collagen synthesis — both endogenous and possibly supplement-stimulated. Collagen peptides stimulate fibroblasts; fibroblasts require vitamin C as a cofactor for the hydroxylation step in collagen strand formation.

A person supplementing collagen while deficient in vitamin C is working against themselves. If you use collagen, pair it with adequate vitamin C from food (citrus, bell peppers, kiwi, broccoli) or supplementation.

Leave a comment

To your zenith within,

Sara Redondo, MD, MS

Resource:

Ravindran R, Pizzol D, Lopez-Gil JF, et al. Collagen supplementation for skin and musculoskeletal health: an umbrella review of meta-analyses on elasticity, hydration, and structural outcomes. Aesthetic Surg J Open Forum. 2026;8:ojag018. doi:10.1093/asjof/ojag018

Cortisol has developed a reputation in wellness culture as the villain of modern life, something to suppress or detox. This is precisely the wrong frame.

Cortisol is not a toxin. It’s one of the most precisely designed survival hormones in human biology. Its job, when working correctly, is essential. The problem is not cortisol itself, but a system that cannot turn off.

Every morning, roughly 20-30 minutes after you wake up, your cortisol levels surge 50-160% above their overnight lows. This is the cortisol awakening response (CAR) — a deliberate, adaptive biological signal that does several necessary things simultaneously.

It mobilizes glucose from the liver, giving your brain and muscles an energy substrate before you have eaten. It sharpens cognitive focus, improving the speed and accuracy of early-morning decisions. It modulates the immune system, briefly suppressing inflammation to allow the body to redirect resources toward activity. It coordinates with your circadian clock to synchronize dozens of other hormonal and metabolic signals.

By midday, cortisol should be declining. By evening, it should be approaching its daily minimum. By the time you sleep, it should be low enough to allow slow-wave sleep and the biological repair processes that depend on it.

This curve — steep in the morning, declining through the day, low by night — is the signature of a well-regulated HPA axis. It’s the pattern that research consistently associates with lower inflammatory markers, better metabolic health, clearer cognition, and longer life.¹

The problem begins when the curve flattens.

Subscribe now

What Happens When the System Cannot Turn Off

Chronic stress — occupational, relational, financial, physical, or any sustained demand that outpaces recovery — disrupts the negative feedback loop that should turn cortisol off once the stressor has passed.¹ The result is a system in which cortisol is sometimes too high at the wrong times, sometimes too low at the wrong times, and almost always dysregulated in its daily rhythm.

The downstream consequences of this dysregulation reach every major organ system in the body. Here is what the evidence documents.

Visceral fat accumulation. Visceral adipose tissue contains approximately four times more glucocorticoid receptors than subcutaneous fat. When cortisol is chronically elevated, it preferentially deposits fat deep in the abdomen — not as a cosmetic problem, but as a metabolic one. Visceral fat is the most pro-inflammatory fat depot in the body, releasing cytokines that further dysregulate the HPA axis. The cycle feeds itself.¹ Cushing’s syndrome — the condition caused by pathologically elevated cortisol — provides the clearest demonstration: virtually every Cushing’s patient develops central obesity, regardless of caloric intake.

Thyroid conversion block. The thyroid gland produces mostly T4, an inactive precursor. T4 must be converted to T3 — the active form — by deiodinase enzymes primarily in the liver and kidney. Cortisol suppresses the activity of 5’-deiodinase, the enzyme responsible for this conversion. Under chronic stress, T4 is redirected away from active T3 and toward reverse T3, an inactive hormone that competes with T3 for receptor binding.¹ The result is a functional hypothyroid state: fatigue, slowed metabolism, cold intolerance, low mood, difficulty concentrating — with a TSH that looks completely normal, because the problem is in the conversion, not in the thyroid’s production.

Insulin resistance. Cortisol raises blood glucose by stimulating hepatic glucose production and reducing insulin sensitivity in peripheral tissues. This is adaptive in acute stress — you need available glucose to fight or flee. Chronically, it’s destructive. Sustained cortisol elevation keeps blood glucose elevated, demands more insulin from the pancreas, and progressively reduces the sensitivity of glucose transporters.¹ Insulin resistance, visceral fat, and HPA dysregulation form a mutually reinforcing triad that is very difficult to interrupt from any single point.

Sleep architecture destruction. Cortisol and slow-wave sleep are directly antagonistic: deep sleep suppresses cortisol; cortisol suppresses deep sleep. When evening cortisol is elevated, slow-wave sleep is compressed. The overnight repair processes that depend on it — cellular maintenance, glymphatic clearance, immune consolidation, NAD+ restoration — are shortened.¹ The 3am waking pattern is the clinical signature of this: cortisol begins its morning ascent too early, crossing the threshold that triggers wakefulness before the biological morning has arrived.

Hippocampal damage. The hippocampus is the brain’s primary hub for memory encoding, emotional regulation, and context processing. It also has the highest density of glucocorticoid receptors of any brain structure — which means it’s both cortisol’s most important target and its most vulnerable victim. Prolonged cortisol elevation causes hippocampal neuronal atrophy, reduces the production of BDNF (the growth factor that maintains neuronal health), and impairs the hippocampal regulation of the HPA axis itself.¹ The result is a self-amplifying loop: stress damages the very brain region responsible for moderating the stress response.

Immune dysregulation. Acute cortisol is powerfully anti-inflammatory — it’s why synthetic glucocorticoids like prednisone are used to treat inflammatory conditions. Chronic cortisol, however, produces glucocorticoid receptor resistance: the immune system becomes desensitized to cortisol’s anti-inflammatory signals while remaining activated by other inflammatory triggers.¹ The paradox is that chronically stressed people are simultaneously cortisol-saturated and more inflamed than their unstressed counterparts — the system that was designed to suppress inflammation has lost its ability to do so effectively.

Share

What a Standard Cortisol Test Cannot Tell You

A single morning blood cortisol measurement — which is the extent of cortisol assessment in standard primary care — tells you almost nothing useful about HPA axis function. It captures one point on a curve that should be dynamic, rhythmic, and context-dependent.

What actually matters is the shape of the diurnal cortisol profile: how steep is the morning rise, how rapidly does it decline through the day, and how low does it reach by evening. A flattened slope — where morning cortisol is lower than it should be and evening cortisol higher than it should be — is the biological signature of chronic stress and burnout, and it’s one of the most consistent predictors of adverse health outcomes in the longitudinal cortisol literature.¹

The most accessible clinical assessment is the cortisol awakening response test — saliva samples collected immediately upon waking, 15 minutes after waking, and 30 minutes after waking. This is available through home collection kits and several functional medicine laboratories. It’s not available on a standard GP or internist panel, and this is a significant gap in routine preventive assessment.

The DUTCH test (Dried Urine Test for Comprehensive Hormones), provides a full diurnal cortisol curve, cortisol metabolites, and the HPA axis markers that reveal whether the system is compensating, depleted, or hyperactivated. It’s the most comprehensive non-invasive assessment of cortisol dynamics currently available to consumers.

The paid section covers what the evidence actually supports for resetting the HPA axis — with specific doses, specific formats, and the crucial nuances that most content on this topic misses entirely. Including the exercise finding that directly contradicts what most people believe about stress and physical intensity, the ashwagandha data that shows something important that most ashwagandha advocates don’t mention, and the sleep intervention that has a larger effect on cortisol regulation than any supplement in the literature.

Read more

Two hospital cleaners work the same floor, the same shift, the same job description.

The first empties bins, mops, restocks, and counts the hours until the end of the day.

The second does all of that — and also rearranges the artwork on the walls of comatose patients so there is something new to see if they wake up. She times her visits to coincide with moments when frightened families need a few minutes of company. She learns which patients have no visitors and lingers a little longer in their rooms. She does not think of herself as part of the janitorial staff. She thinks of herself as part of the team that heals people.

Same wage. Same contract. Same tasks on paper. Two completely different experiences of being alive at work.

When Amy Wrzesniewski and Jane Dutton published their study of hospital cleaning staff in 2001, they described what the second group of cleaners was doing as job crafting — a conscious or unconscious redesign of their role to connect it to something that felt meaningful.¹

What they also found was that this group reported substantially greater wellbeing, engagement, and satisfaction. They were not pulling themselves up by their bootstraps and whistling through a hard job. They were, as Wrzesniewski put it, doing a different job.

That study lived in organizational psychology for two decades. Then the medical literature caught up with it. And what the data now shows about purpose in life and health outcomes is not what most people expect.

Subscribe now

What the Research Shows

Purpose in life is defined in the research literature as a person’s sense of having meaningful goals and directions that guide them through life.

It’s measured quantitatively, across validated scales, in samples large enough to detect small effects. It predicts health outcomes independently of income, education, physical activity, and existing disease.

The Depression Data Is the Most Striking

A 2023 meta-analysis of 99 studies covering 66,468 participants found that greater purpose in life was significantly associated with lower depression, with a mean weighted effect size of r=-0.49.²

To put that in context: that is a larger association than most pharmacological and psychological interventions for depression show in head-to-head trials. The association held across age groups, cultures, and clinical and non-clinical populations.²

The most recent test came from a 2026 individual-participant meta-analysis of 72 samples totaling 531,038 participants across six world regions, from North America to East Asia to sub-Saharan Africa.³ The inverse association between purpose and depressive symptoms was consistent everywhere.

The Mortality Data Is Even More Surprising

A study using UK Biobank data from 153,505 adults followed for up to six years found that every standard deviation higher in meaning in life was associated with a 15% decrease in all-cause mortality.⁴

This remained significant after adjusting for socioeconomic status, clinical conditions, and every behavioral risk factor measured — including physical activity and smoking.⁴

The Dementia Data Is the Most Recent

A UC Davis longitudinal study followed 13,765 adults aged 45 and older for up to 15 years. Those in the top third for purpose in life had a 28% lower risk of developing mild cognitive impairment or dementia compared to those in the lowest third — after adjusting for age, education, depression, and the presence of the APOE4 allele, the strongest known genetic risk factor for Alzheimer disease.⁵

Even in people who carry APOE4, a stronger sense of purpose was associated with delayed onset of cognitive decline.

Share

This Is NOT Positive Thinking

Purpose does not improve health outcomes because optimism is good for you. It improves health outcomes through measurable biological pathways.

People with a stronger sense of purpose have lower levels of inflammatory markers — including the same interleukin-6 and C-reactive protein that appear throughout the cardiovascular and cancer prevention literature as independent risk factors.

They have lower cortisol reactivity to stressors and faster cortisol recovery. They sleep better. They are more likely to engage in health-promoting behaviors — not because they are more disciplined, but because a sense of future mattering makes the present worth protecting.

The second hospital cleaner was not just happier. She was, in all probability, healthier in ways that would have shown up on a blood panel.

The most important clinical implication: low sense of purpose belongs in the same preventive conversation as blood pressure, blood glucose, and hs-CRP.

The paid section covers what the evidence actually supports for building and maintaining a sense of purpose, backed by randomized controlled trial data. Including the psychological approach with the strongest RCT evidence for depression that most people have never heard of, the behavioral intervention with a 22% mortality effect in meta-analysis, and the reframe that applies to people whose capacity to achieve or create has been limited by illness, age, loss, or circumstance.

Read more

I’ve thought many times about what I would write on this anniversary. I didn’t want to write something small. I wanted to write something that honored her in the most useful way I know, by turning what her illness taught me into something that might prevent it in someone else.

My mother died of ovarian cancer. Her mother died of ovarian cancer before her. Her grandmother had breast cancer.

Three generations of women in my family. Three of the same cancers. The same pattern, moving through the family line, doing damage nobody knew how to stop.

I haven’t had genetic testing done yet. That decision carries more weight than it might appear, and it’s a step I’m still navigating.

But I don’t need a lab result to understand what this family history is telling me. Three generations, the same cancers, the same line. Whether or not there’s a confirmed mutation in my file, that pattern changes how I think about my own body, and how I practice medicine.

The framework I’m about to share — the exact tests I monitor, the lifestyle decisions I make, and the conversation tool at the end of this post — is what I give my patients. Today I’m giving it to you, for free, because ten years of absence has made one thing clear: the information that changes outcomes needs to reach people before the diagnosis, not after it.

Subscribe now

Cancer by the Numbers

Cancer is the defining disease of our era.

In 2022, close to 20 million new cancer cases were diagnosed worldwide, alongside 9.7 million deaths.¹ By 2050, the global cancer burden is projected to reach 35 million new cases annually — driven by population growth, aging, and the global spread of Western lifestyle risk factors.¹

Around 1 in 9 men and 1 in 12 women will die from it.¹ Lung cancer is both the most commonly diagnosed cancer globally (12.4% of all cancers) and the leading cause of cancer death (18.7% of all cancer deaths). The next most common cancers worldwide are breast, colorectal, prostate, and stomach.¹

Cancer is already the leading cause of death ahead of cardiovascular disease in several high-income regions, and it’s on a trajectory to become the leading cause of death globally this century.¹

Here is the number that matters most for everything that follows:

40% of all cancer cases in the United States — and a comparable proportion globally — are attributable to modifiable risk factors: cigarette smoking, excess body weight, alcohol consumption, physical inactivity, poor diet, and preventable infections.²

Forty percent.

Not in people with good genetics only. In everyone. Including people with a hereditary predisposition. Including me.

The gene I may carry does not exempt me from the modifiable portion of that risk. It makes the modifiable portion more important.

My mother’s generation didn’t have this framework. The conversation between a patient with a family history of cancer and her doctor was structured around surveillance — watching and waiting.

I’m not willing to only watch and wait.

Leave a comment

What a Family History Like Mine Likely Means

Three generations of ovarian and breast cancer in the direct female line is the clinical picture most strongly associated with hereditary breast and ovarian cancer syndrome — most commonly driven by a pathogenic mutation in BRCA1 or BRCA2.

BRCA1 and BRCA2 are tumor suppressor genes that work constantly to identify and repair DNA damage. When these genes carry a pathogenic mutation, that quality control is compromised and the risk of certain cancers rises dramatically.

Women carrying a BRCA1 or BRCA2 pathogenic mutation have up to a 72% lifetime risk of breast cancer, compared to approximately 12-13% in the general population. The lifetime risk of ovarian cancer with a BRCA1 mutation is 44% compared to about 1% in the general population.³

BRCA mutations also increase risk of pancreatic cancer, fallopian tube cancer, peritoneal cancer, and melanoma, depending on the specific mutation. Men with BRCA2 mutations carry elevated risk of breast, prostate, and pancreatic cancer.

What a mutation does not mean is certainty. It means elevated probability. And probability, shaped by everything else in this post, is not fixed.

If you have a first- or second-degree relative with breast cancer before age 50, or any relative with ovarian cancer, ask your doctor for a referral to a cancer genetics specialist. Knowing changes your clinical management — and your family’s options.

Share

The Levers I Actually Pull

These are the specific decisions I make about my own body, grounded in the evidence I’ve spent years reviewing as a clinician and a researcher.

Alcohol — The One I Take Most Seriously

The evidence here is the clearest and the most ignored.

In January 2025, the US Surgeon General issued a formal advisory stating there is no safe level of alcohol consumption when it comes to cancer risk — naming esophageal, liver, colorectal, oral, throat, laryngeal, and breast cancer as all causally linked to alcohol consumption.⁴

Alcohol is the third largest modifiable cause of cancer in the United States, behind smoking and excess body weight.²

A 2024 systematic review and meta-analysis specifically on breast cancer confirmed that consuming less than one standard drink per day still significantly increases breast cancer risk.⁵

The most recent meta-analysis on breast cancer specifically, published in 2026, found that any alcohol consumption was associated with a 17% higher risk overall — with a clear dose-response: light drinking 13% higher, heavy drinking 52% higher.⁶

Subscribe now

The mechanism for breast cancer is well characterized: alcohol raises estrogen levels through inhibition of estrogen metabolism, direct effects on aromatase enzyme activity, and reduction of folate bioavailability, which impairs DNA repair. For other alcohol-associated cancers, separate mechanisms — including direct acetaldehyde toxicity and oxidative stress — are responsible.

With a family history like mine, I don’t drink. The risk-to-benefit ratio for someone in my position is, in my clinical judgment, not acceptable. This is a decision I made after reading the evidence.

Exercise

A Dutch nationwide retrospective cohort study of 725 BRCA1/2 mutation carriers found that sports activity after age 30 was significantly inversely associated with breast cancer risk — a 37% lower risk in active carriers compared to inactive carriers.⁷

More broadly, the cancer prevention evidence for physical activity spans both sexes and multiple cancer types — colorectal, breast, endometrial, bladder, kidney, gastric, and lung cancer all show consistent inverse associations with physical activity in large meta-analyses.²

The mechanisms operate across cancer types: exercise reduces adipose tissue, improves insulin sensitivity, reduces systemic inflammation, and enhances immune surveillance — the body’s capacity to identify and eliminate precancerous cells.

The cancer prevention evidence supports a minimum of 150 minutes of moderate-intensity aerobic activity per week, plus resistance training. This is the same threshold as the cardiovascular benefit evidence. The health systems overlap.²

Share

Body Composition — Specifically Visceral Fat

Excess body weight accounts for 7.6% of all cancer cases in the United States — affecting both men and women — and is causally linked to at least 13 cancer types, including colorectal, pancreatic, liver, kidney, esophageal, endometrial, breast, and advanced prostate cancer.²

One key mechanism is aromatase: an enzyme expressed in adipose tissue, particularly visceral fat, that converts androgens to estrogen. The more visceral fat, the more estrogen produced peripherally, independently of the gonads. This drives hormone-sensitive cancer risk in both men and women.

Beyond aromatase, elevated adiposity promotes insulin resistance and chronic inflammation, both of which create a cancer-permissive environment through separate pathways.

Chronic Inflammation — the Biomarker I Monitor Most Carefully

Elevated circulating inflammatory markers are associated with increased risk of colorectal, lung, and several other cancers in large epidemiological studies. In the context of breast cancer specifically, a meta-analysis of prospective studies found that the highest CRP levels were associated with a 13% higher risk compared to the lowest levels.⁸

Inflammation creates a permissive environment for cancer development: it impairs immune surveillance, promotes angiogenesis (the new blood vessel formation that tumors require), and generates reactive oxygen species that damage DNA. It is also the common downstream pathway through which excess visceral fat, sedentary behavior, poor diet, and chronic psychological stress all increase cancer risk.

Sleep — Immune Surveillance You Can’t Outsource

The immune system’s capacity to identify and eliminate precancerous cells — immune surveillance — is substantially impaired by sleep deprivation.

Natural killer (NK) cell activity, one of the primary mechanisms by which the immune system identifies and destroys abnormal cells, is reduced by up to 70% after a single night of four to five hours of sleep in human studies. Chronic sleep insufficiency is associated with higher cancer incidence across multiple large epidemiological cohorts.

Diet — the Methyl Donor Protocol

DNA repair — the same process that BRCA genes are partially responsible for — depends critically on methylation: a chemical process that regulates gene expression and enables repair. Methyl donor nutrients — folate, choline, methionine, B12, B6 — directly support this process.

The Conversation I Have Every Year

Because of my family history, I bring a blood panel to every appointment that my general practitioner did not initially know to order. I had to ask for it, and I had to explain why I was asking.

That’s the piece I want to change for you.

Subscribe now

Most people with a family history of cancer receive excellent surveillance recommendations and very little guidance on what else to monitor, what lifestyle data to bring to appointments, and what questions to ask. The conversation tends to focus on screening modalities — not on hs-CRP, not on insulin resistance, not on the 40% of cancer risk that sits in modifiable territory.

Below is the tool I’ve built for you to take to your next appointment. Print it or screenshot it. Hand it directly to your doctor and say: I’d like to discuss these.

Leave a comment

Your Cancer Prevention Conversation

Print this page or screenshot it and bring it to your next appointment.

PART 1 — Biomarkers to Request

• hs-CRP (high-sensitivity)

  • Target: below 1.0 mg/L

  • Chronic inflammation is an independent risk factor for breast, ovarian, and colorectal cancer.

• Fasting insulin + HOMA-IR

  • Target: HOMA-IR below 1.5

  • Insulin resistance promotes cancer cell proliferation and is detectable a decade before HbA1c changes.

• HbA1c

  • Target: below 5.7%

  • Elevated glucose creates a cancer-promoting metabolic environment.

• 25-OH Vitamin D

  • Target: 75-125 nmol/L (30-50 ng/mL)

  • Low vitamin D is associated with higher risk of breast, colorectal, and ovarian cancer.

• ApoB

  • Target: below 90 mg/dL

  • A marker of metabolic health; elevated in insulin resistance.

• Ferritin

  • Target: 50-100 ng/mL

  • Iron deficiency impairs immune function; elevated ferritin reflects inflammation.

• Waist circumference

  • Target: below 80 cm (31.5 in) for women / below 94 cm (37 in) for men

  • Visceral fat drives aromatase activity, insulin resistance, and systemic inflammation — all independent cancer risk factors.

Request these alongside your standard annual blood work. Tell your doctor: “I’d like to discuss these as part of my cancer prevention monitoring.”

Subscribe now

PART 2 — Lifestyle Factors to Discuss With Your Doctor

• Alcohol: Ask: “What is my current risk from alcohol consumption given my family history?” The US Surgeon General’s 2025 advisory identifies alcohol as a cause of at least seven cancers — esophageal, liver, colorectal, oral, throat, laryngeal, and breast — with no established safe threshold. This conversation is almost always skipped.

• Exercise: Tell your doctor your current weekly activity volume and type. Ask: “Am I meeting the evidence-based minimum for cancer risk reduction — 150 minutes of moderate activity per week — and am I doing resistance training?”

• Body composition: Ask for waist circumference measurement alongside weight. Waist-to-height ratio below 0.5 is more predictive of cancer risk than BMI alone.

• Sleep: Disclose your average sleep duration and quality honestly. Ask: “Is there anything in my current sleep picture that could be impairing my immune surveillance?”

• Chronic stress: Sustained HPA axis activation impairs immune function and promotes the inflammatory state associated with cancer development. Ask: “Is there a validated tool you use to assess stress-related immune suppression?”

Leave a comment

PART 3 — Screening Reminders for Anyone With a Cancer Family History

Breast (for those with family history or confirmed BRCA mutation):

• Annual MRI from age 25 (NCCN 2025 for BRCA carriers and high-risk family history)

• Annual mammography from age 30 (add to MRI, not replace)

• Clinical breast exam every 6-12 months from age 25

• If your personal family history is unclear: ask for a formal risk assessment using a validated model (BOADICEA, Tyrer-Cuzick)

Ovarian and gynecological:

• No screening method has been proven to detect ovarian cancer early enough to reliably improve survival (CA-125 and transvaginal ultrasound have not met this bar)

• If BRCA-positive: discuss prophylactic bilateral salpingo-oophorectomy timing with a gynecological oncologist — typically recommended between ages 35-40 for BRCA1, 40-45 for BRCA2, or after completion of childbearing

• Annual gynecological examination

Colorectal: Colonoscopy from age 45 (average risk) or earlier if family history of colorectal cancer. Currently the most preventable of the major cancers.

General: Skin cancer — annual dermatological skin check if you have significant sun exposure history or a family history of melanoma.

Genetic:

• If you have not had genetic testing and have a first- or second-degree relative with breast cancer before age 50, or any relative with ovarian cancer: ask for referral to a cancer genetics specialist

• First-degree relatives of a confirmed BRCA carrier should be offered testing

• Consider testing yourself — knowing changes your clinical management and your family’s options

Share

Why I’m Sharing This

I have a family history that tells a clear story, a ten-year absence that reminds me of what’s at stake, and the tools of preventive medicine to do everything the evidence supports.

I’m sharing this because the conversation I describe above is a conversation most people with elevated cancer risk never have. Not because the evidence doesn’t exist. Definitely that is not the reason. But because nobody has shown them what to ask.

My mother deserved that conversation. She didn’t get it. I’m making sure you do.

Subscribe now

To your zenith within,

Sara Redondo, MD, MS

P.S. I’d love to read you. If this made you think of your own family history, your loved ones, your body, or a question you’ve been carrying, leave a comment. I’ll be answering every one. ❤️

Leave a comment

References:

1. Bray F, Laversanne M, Sung H, et al. Global cancer statistics 2022: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin. 2024;74(3):229-263. doi:10.3322/caac.21834

2. Islami F, Marlow EC, Thomson B, McCullough ML, Rumgay H, Gapstur SM, Patel AV, Soerjomataram I, Jemal A. Proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors in the United States, 2019. CA Cancer J Clin. 2024;74(5):405-432. doi:10.3322/caac.21858

3. Kuchenbaecker KB, Hopper JL, Barnes DL, et al. Risks of breast, ovarian, and contralateral breast cancer for BRCA1 and BRCA2 mutation carriers. JAMA. 2017;317(23):2402-2416. doi:10.1001/jama.2017.7112

4. US Department of Health and Human Services, Office of the Surgeon General. Surgeon General’s Advisory on Alcohol and Cancer Risk. January 2025. Available at: https://www.hhs.gov/sites/default/files/oash-alcohol-cancer-risk.pdf

5. Sohi G, Lam JE, Brooks PJ. Alcoholic beverage consumption and female breast cancer risk: a systematic review and meta-analysis of prospective cohort studies. Alcohol Clin Exp Res. 2024;48:2222-2241. doi:10.1111/acer.15493

6. Arecco L, Cacilhas PM, Bobato Lara Gismondi C, et al. Association between alcohol consumption and breast cancer incidence and prognosis: a systematic review and meta-analysis. The Breast. 2026;86:104719. doi:10.1016/j.breast.2026.104719

7. Pijpe A, Manders P, Brohet RM, et al. Physical activity and the risk of breast cancer in BRCA1/2 mutation carriers. Breast Cancer Res Treat. 2010;120(1):235-244. doi:10.1007/s10549-009-0476-0

8. Lou MWC, Drummond AE, Swain CTV, et al. Linking physical activity to breast cancer via inflammation, part 2: the effect of inflammation on breast cancer risk. Cancer Epidemiol Biomarkers Prev. 2023;32(5):597-605. doi:10.1158/1055-9965.EPI-22-0929

Here is something that will change how you think about chronic disease.

You already know that cells divide, grow old, become damaged, and die. That death —called apoptosis — is healthy and essential. Old or damaged cells are cleared away, making room for new ones. The body renews itself through continuous cycles of death and replacement.

Some cells stop cooperating with this plan.

When a cell accumulates too much DNA damage, oxidative stress, or oncogenic signaling, it reaches a decision point. It can keep dividing (risking becoming cancerous) or it can stop. The safe choice is to arrest permanently: to stop dividing, stop functioning as a normal cell, and wait to be cleared by the immune system.

The problem is what happens when the immune system can’t keep up.

These arrested cells — called senescent cells — don’t die. They persist in tissues for years, sometimes decades. They resist the normal apoptosis signals that would eliminate them. And they don’t just sit quietly. They secrete a continuous stream of pro-inflammatory molecules, growth factors, proteases, and immune-activating signals that researchers have named the Senescence-Associated Secretory Phenotype, or SASP.¹

And here is the detail that makes this genuinely alarming: the SASP is “contagious.”

When a senescent cell secretes its inflammatory cocktail into surrounding tissue, it can convert neighboring healthy cells into senescent cells through the same signaling cascades. One senescent cell begets more. The burden spreads through the molecular environment the SASP creates. This is why senescent cells accumulate exponentially with age rather than linearly. Once the immune system starts losing the clearance battle, the accumulation accelerates.

This spreading mechanism is why researchers sometimes call them zombie cells. They can’t live, they won’t die, and they bite.

Subscribe now

What a Senescent Cell Secretes and Why It Matters Across the Entire Body

The SASP is a heterogeneous mixture that varies by cell type and context, but consistently includes: pro-inflammatory cytokines (IL-6, IL-8, TNF-alpha), matrix metalloproteinases that degrade the structural scaffolding of tissues, growth factors that paradoxically promote tumor growth in neighboring cells, and chemokines that recruit immune cells — initially clearing senescent cells, but over time contributing to chronic tissue inflammation.¹

IL-6 alone — one SASP component — is an independent predictor of all-cause mortality, cardiovascular events, and cognitive decline in multiple large cohort studies. It’s the same cytokine that drives the acute systemic inflammatory response in severe infections. In senescent cells, it’s produced continuously at lower levels, for years.

The SASP is also why senescent cells are a unifying mechanism behind diseases that appear unrelated.

• Senescent fat cells in visceral adipose tissue secrete SASP factors that drive insulin resistance and metabolic dysfunction.

• Senescent vascular endothelial cells secrete SASP components that impair nitric oxide production and drive arterial stiffness, leading to hypertension.

• Senescent microglia in the brain release pro-inflammatory signals that accelerate neuroinflammation and tau propagation in Alzheimer’s disease.

• Senescent osteoblasts contribute to the imbalance between bone formation and resorption underlying osteoporosis.

The specific cellular context changes, but the SASP mechanism is the same.¹

Share

The Mouse Data That Changed the Field

Two findings from mouse studies established senescent cells as a central target in aging research, and both were so striking that they would be hard to believe without the published evidence.

Finding 1

In 2016, researchers engineered mice to clear their own p16-positive senescent cells when given a specific drug signal. They then gave the drug intermittently to naturally aging mice.

The result: clearing senescent cells significantly extended healthy lifespan in both male and female mice, delayed multiple age-related tissue dysfunction pathologies, and, critically, appeared to work even when the intervention began in middle age rather than birth.²

“Naturally occurring p16Ink4a-positive cells shorten healthy lifespan,” the paper’s title stated without hedging.

Finding 2

In 2018, researchers took senescent cells from old mice and transplanted them into young, healthy mice. Within just two weeks, the young mice began showing features of aging — physical dysfunction, reduced strength, frailty, reduced activity.

Then the researchers treated these young mice — which had been artificially aged by the transplantation — with senolytic drugs that killed the transplanted senescent cells. Physical function recovered.³

Young mice. Made frail by senescent cell injection. Restored by killing those cells.³

These are not human trials. The caution that applies to all mouse-to-human translational research applies here. But the mechanistic clarity — senescent cells cause the dysfunction, removing them reverses it — is what drove an entire generation of researchers toward human trials.

Subscribe now

The Twist That Makes This More Complex

Here is where the story gets more nuanced.

Not all senescent cells are harmful.

Cellular senescence serves genuine biological purposes. It’s the primary anti-cancer mechanism in most tissues — when a cell begins acquiring the genetic changes that precede malignancy, senescence halts it before it can proliferate. Senescent cells play roles in embryonic development and tissue morphogenesis. And they participate in wound healing and tissue repair, at least transiently.

A 2024 paper published in Nature Aging made this distinction precise for the first time at the molecular level.⁴

Researchers at the University of Connecticut, using a cutting-edge spatial transcriptomics technique called Xenium, mapped the exact distribution of different senescent cell populations in healing skin wounds. They found two distinct populations: p16-expressing senescent cells, which had previously been shown to assist wound closure, and a newly characterized p21-expressing population that had a strongly pro-inflammatory profile — and was actively hindering healing.

When they selectively cleared the p21-high cells, wound healing accelerated. When they left the p16-high cells intact, healing remained normal.⁴

This is the finding that changes the intervention framework: blanket elimination of all senescent cells is not the goal. The goal is selective clearance of the harmful populations — specifically the chronically accumulated, pro-inflammatory, SASP-secreting senescent cells that accumulate with aging. The transiently senescent cells serving wound repair and tumor suppression should, ideally, remain.

A 2026 review published in Aging confirmed this emerging view: senescent pancreatic beta cells show superior insulin secretory capacity relative to younger cells. Senescent glial cells, by contrast, are key drivers of neuroinflammation and cognitive decline.⁵ The same cell fate, in different tissues, with opposite functional consequences.

This is why the field has moved from “senescent cells are bad, eliminate them” to “senescent cell accumulation is bad, target the harmful populations, understand the heterogeneity.” It’s a more sophisticated position, and it’s the accurate one.

What Accumulates Senescent Cells

The biological processes driving senescent cell accumulation are well characterized. Some are largely inevitable with aging. Most are substantially modifiable.¹

• DNA damage and oxidative stress are the primary inducers of senescence at the cellular level. Every source of chronic oxidative damage — tobacco smoke, alcohol, hyperglycemia, ultra-processed diet, chronic inflammation — increases the rate at which cells accumulate the damage that triggers senescent arrest. Higher lifetime oxidative stress load translates directly to higher tissue senescent cell burden.

• Telomere shortening occurs with every cell division. When telomeres reach a critical length, they generate a DNA damage signal that induces senescence. This is why tissues with high cellular turnover — the gut lining, the immune system, the skin — accumulate senescent cells faster. And telomere shortening is accelerated by the same lifestyle factors that accelerate epigenetic aging: chronic psychological stress, poor sleep quality, smoking, obesity, sedentary behavior.

• Chronic psychological stress induces senescence through sustained cortisol-mediated DNA damage and mitochondrial dysfunction. Part of the mechanistic pathway runs directly through senescent cell accumulation.

• Adiposity — particularly visceral fat — is itself a site of substantial senescent cell accumulation, and senescent fat cells are among the most potent SASP producers. This is part of why excess visceral adiposity drives systemic inflammation and metabolic dysfunction beyond what caloric excess alone would predict.

• Immune senescence — the aging of the immune system itself — reduces the efficiency of senescent cell clearance. The immune system normally identifies and eliminates senescent cells through specific surface markers. When immune surveillance declines with age, the clearance process becomes less efficient, allowing the burden to accumulate further.

Why This Is Not Yet in Your Doctor’s Toolkit

The drug interventions that target senescent cells — called senolytics — are among the most actively investigated therapeutic targets in the entire aging research field.

More than 20 human clinical trials are currently registered on ClinicalTrials.gov targeting senescent cells. The mechanistic case for senolytics is stronger than almost anything else in the longevity pipeline.

They are also not yet in clinical guidelines, not covered by insurance, and not available as a standard prescription for aging-related disease. Some are available over-the-counter in the form that partially overlaps with the trial doses; others require off-label use of prescription drugs outside their approved indications.

Below, you have what the first human trials actually showed about physical function and senescent cell clearance, the distinction between the pharmaceutical senolytics, the natural senolytics with emerging animal and human evidence, and the lifestyle inputs that most powerfully reduce senescent cell accumulation, with the specific evidence for each.

Read more

You’ve had a birthday every year for your entire life, so you know your chronological age to the day.

However, this number, used to calculate your cardiovascular risk on every clinical decision support tool your doctor uses, is the least accurate measure of how your body is actually aging.

Two people born in the same year can walk into a clinic today with biological ages a decade apart. One set of cells is running on a 50-year-old timeline. The other is running on a 40-year-old timeline. Neither the patients nor their doctors can tell the difference from the outside. The cholesterol panels, the blood pressure readings, the BMI… None of these measures distinguish between the two trajectories until something goes wrong.

Until recently, we couldn’t tell the difference either. Now we can.

What DNA Methylation Actually Is

Your DNA is fixed. Every cell in your body carries the same genetic sequence you were born with, and it doesn’t change. But layered on top of that fixed sequence is a second layer of information — a pattern of chemical marks attached to your DNA that control which genes are turned on and which are silenced, without altering the sequence itself. This is epigenetics.

The most studied of these marks is DNA methylation: the addition of a methyl group to specific sites (called CpG sites) along the genome. Methylation at a given site typically silences the gene below it. The pattern of methylation across thousands of these sites changes systematically with age, with lifestyle, with disease, and with environmental exposure.

In 2013, biostatistician Steve Horvath made a discovery that changed the field: the pattern of DNA methylation across 353 specific CpG sites predicted a person’s chronological age with remarkable accuracy. A blood sample from a 55-year-old looked different from a sample from a 35-year-old, even before any clinical disease appeared. The methylation pattern was, in effect, a biological timestamp.

He called it an epigenetic clock. The timestamp it kept was not identical to the calendar.

Subscribe now

The Clocks That Followed — and Why the Generation Matters

Horvath’s first clock was a proof of concept: yes, methylation tracks age. But it predicted chronological age, not health. It told you how old your cells looked. It didn’t tell you how fast they were aging or how likely you were to get sick.

The second and third generation clocks fixed this by training on outcomes that actually matter — mortality, disease incidence, functional decline — rather than simply the passage of time. The result is a set of biological age measures with meaningfully different predictive power.¹

PhenoAge (Levine, 2018) was trained on a composite of nine clinical biomarkers — albumin, creatinine, glucose, CRP, lymphocyte percentage, red cell volume, red blood cell distribution, alkaline phosphatase, and white blood cell count — that together predict biological fitness. PhenoAge predicts all-cause mortality better than the original Horvath clock and shows meaningful associations with lifestyle factors.

GrimAge (Lu, 2019) was the leap. Rather than using clinical biomarkers, GrimAge used DNA methylation-based surrogates for plasma proteins — including GDF-15, adrenomedullin, and the cystatin C signaling associated with kidney aging — combined with a DNA methylation surrogate for lifetime smoking pack-years. Trained specifically to predict time-to-death, GrimAge is the most consistently validated mortality predictor in the epigenetic clock literature across populations, tissues, and follow-up periods.¹

The mortality data on GrimAge is precise and striking.

A 2025 retrospective cohort study of 1,942 NHANES participants found that GrimAge and GrimAge2 age acceleration were significantly and positively associated with all-cause, cancer-specific, and cardiac mortality — the only clocks among eleven tested to show these associations across all three outcome categories.²

In studies that have calculated hazard ratios by year of biological age acceleration, GrimAge EAA per 5-year increase predicts roughly a 50% increase in all-cause mortality and a 55% increase in cardiovascular mortality, after adjustment for conventional risk factors.²

Independent of blood pressure, cholesterol, BMI, and smoking history.

DunedinPACE (Belsky, 2022) is the most conceptually distinct of the major clocks, and arguably the most useful for the person trying to change something.³ Where GrimAge estimates your cumulative biological age, DunedinPACE estimates your pace of aging: how many biological years you are accumulating per calendar year right now. The scale is intuitive:

• A DunedinPACE of 1.0 means you are aging at the average rate for your chronological age.

• A pace of 0.8 means you are aging more slowly — roughly 80% as fast as average.

• A pace of 1.2 means you are aging 20% faster than average.

Share

DunedinPACE responds more rapidly to lifestyle changes than GrimAge because it measures current pace rather than cumulative history. You can’t undo 30 years of accelerated aging in eight weeks. But you can slow the current pace, and DunedinPACE captures that change faster.

The Finding That Changes What You Think Is Possible

Here is the result that most people in this field find most significant:

A randomized controlled trial led by Kara Fitzgerald published in Aging in 2021 enrolled 43 healthy men aged 50-72 and randomized them to either an 8-week diet and lifestyle intervention (high-phytonutrient and methyl-donor-rich diet, exercise guidance, sleep guidance, breathing-based stress reduction, and targeted supplementation) or a no-intervention control.⁴ Genome-wide DNA methylation analysis was conducted before and after the 8-week period.

The treatment group showed a mean biological age decrease of 3.23 years compared to controls on the Horvath DNAmAge clock. Within the treatment group, participants scored a mean of 2.04 years younger at the end of the program than at the start.⁴

This was the first randomized controlled trial to demonstrate a potential reversal of biological age. Eight weeks. An average of three years younger on the epigenetic clock. In healthy, middle-aged men with no specific disease process to reverse.

This result is preliminary, but the direction of the effect, and the magnitude, are consistent with what the mechanistic evidence would predict: epigenetic marks respond to the inputs you provide.

Change the inputs significantly enough, consistently enough, and the marks shift.

Subscribe now

Why This Is Not on Your Annual Blood Report

The gap between what this technology can measure and what your annual physical captures is one of the most significant mismatches in contemporary preventive medicine.

Biological age testing via epigenetic clocks is not covered by standard insurance panels. It’s not yet integrated into primary care electronic health records. Most general practitioners have not ordered one, and most clinical guidelines have not yet incorporated it.

This is partly a matter of clinical translation timing — the evidence base is robust but relatively young, the standardization between commercial platforms is still developing, and the regulatory and reimbursement infrastructure hasn’t caught up.

A 2026 review published in eBioMedicine specifically noted that “important questions remain about the reliability of these measures in commercial wellness settings and how they should be used in clinical practice,” while simultaneously documenting that the evidence for their predictive validity continues to strengthen rapidly.⁵

Below, you have a complete guide to what the tests actually measure, which commercial formats have the most robust evidence, what to do with the result once you have it, the specific lifestyle factors that move the number fastest and by how much, the women-specific considerations, and what the Fitzgerald intervention program actually containe, in enough detail to replicate the inputs that produced a 3.23-year improvement.

Read more

You’ve probably been told your heart palpitations are from stress. Your digestive problems are IBS. Your anxiety is a mental health issue. Your chronic low-grade inflammation is from your diet. Each one gets a separate appointment, a separate specialist, a separate explanation.

What nobody has told you is that all four may be running on the same circuit.

The vagus nerve is the longest cranial nerve in the body. It wanders (the Latin “vagus” means wandering) from the brainstem down through the neck, into the chest, and through the abdomen, innervating the heart, lungs, esophagus, stomach, small intestine, liver, spleen, and pancreas. It’s the principal highway of the parasympathetic nervous system — the branch responsible for rest, recovery, digestion, immune regulation, and cardiovascular deceleration.

Here is the finding that most people, and many clinicians, don’t know: 80% of the vagus nerve’s fibers carry information from your body to your brain, not the other way around.¹ It’s primarily a surveillance system, not a command cable. Your gut is constantly reporting to your brain through vagal afferents. Your immune organs are sending inflammatory signals upward. Your heart is transmitting its own pressure and chemical status toward the brainstem. The brain then integrates this information and sends its 20% efferent response back downward.

This has profound implications for everything that follows.

What Vagal Tone Actually Means — and Why Your Wearable Is Already Measuring It

Vagal tone is the baseline level of activity in your vagus nerve — how robustly and consistently it regulates the systems it serves.

• High vagal tone means the parasympathetic system is healthy, responsive, and capable of rapid adjustment.

• Low vagal tone means the system is sluggish, autonomic balance has shifted toward sympathetic dominance, and the downstream consequences accumulate across every organ the vagus nerve touches.

Vagal tone isn’t directly measured in a standard clinical assessment. What it is measured by, non-invasively and in real time, is heart rate variability (HRV) — specifically the variation in the time intervals between consecutive heartbeats.²

A healthy heart doesn’t beat like a metronome. The intervals between beats fluctuate continuously as the autonomic nervous system responds to breathing, blood pressure, and other physiological signals. Greater variability reflects greater vagal modulation of the heart. Lower variability reflects reduced vagal influence and relative sympathetic dominance.²

The specific metric your wearable device is tracking — RMSSD on Oura, Whoop, or Apple Watch — is a direct measure of vagally mediated heart rate variability. You’ve been wearing a vagal tone monitor and may not have known it.

Subscribe now

Why This Number Predicts Whether You Live or Die

Low HRV is not an interesting biometric curiosity. It’s an independent predictor of mortality that rivals conventional cardiovascular risk factors in its clinical significance.

A meta-analysis of 28 cohort studies involving 3,094 adults with cardiovascular disease found that low HRV was associated with a 2.12-fold increase in all-cause mortality and a 1.46-fold increase in cardiovascular events, independent of age, sex, and established cardiovascular risk factors.³

The word “independent” is the most important word in that sentence. Because it means that two people with identical cholesterol, blood pressure, and lifestyle habits can have vastly different cardiovascular risk based on something the annual physical never assesses.

Share

The Four Places Your Vagal Tone Matters Most

1. Your Heart

The vagus nerve directly innervates the sinoatrial node — the heart’s pacemaker. Vagal activation slows the heart rate and promotes the parasympathetic recovery between beats that generates healthy HRV. When vagal tone is chronically low, the heart runs hotter, the recovery between beats is compressed, and the cardiovascular system loses the adaptive flexibility that predicts longevity.² This is not just about feeling calm. It’s about the mechanical wear and tear on the cardiovascular system over decades.

2. Your Immune System

The vagus nerve doesn’t just connect the brain to the gut and heart. It runs directly to the spleen and liver, where it activates what researchers call the cholinergic anti-inflammatory pathway: a reflex in which vagal efferent fibers trigger the release of acetylcholine at synaptic junctions with immune macrophages, suppressing the production of pro-inflammatory cytokines including TNF-alpha, IL-1, and IL-6.⁴

When this pathway functions well, it acts as a biological brake on systemic inflammation. When vagal tone is low, the brake is compromised. Chronic low-grade inflammation — the same inflammatory state underlying atherosclerosis, insulin resistance, neurodegeneration, and autoimmune disease — is partly a consequence of inadequate vagal anti-inflammatory suppression.

The clinical evidence that this pathway is therapeutically targetable came from the RESET-RA trial, published in Nature Medicine in 2025: a pivotal, double-blind, randomized, sham-controlled trial in 242 patients with drug-refractory rheumatoid arthritis. Implanted vagus nerve stimulation produced an ACR20 clinical response rate of 35.2% at 3 months compared to 24.2% for sham, improving to 52.8% at 12 months in open-label follow-up, in patients who had failed multiple biologic therapies.⁵

The vagus nerve modulating systemic inflammation is not a theory. It’s a randomized trial result published in the leading medical journal for biological research.

Subscribe now

3. Your Gut

The gut-brain axis is one of the most discussed topics in contemporary medicine, and the vagus nerve is its primary anatomical substrate. Gut microbiota produce metabolites that stimulate vagal afferent fibers in the intestinal lining, sending chemical signals to the brain that influence mood, appetite, cognition, and stress responses.⁶ The gut and the brain are in constant conversation — and 80% of that conversation travels upward, from gut to brain, via the vagus nerve.¹

When gut microbial diversity is disrupted — through ultra-processed food, antibiotics, chronic stress, or sedentary lifestyle — the chemical signals reaching vagal afferents change. The brain receives different information. Vagal tone is affected by gut health, and gut health is affected by vagal tone. This is the bidirectionality that makes the gut-brain axis so difficult to address from one direction alone.

4. Your Mental Health

People with anxiety disorders have significantly lower vagal-related HRV than healthy controls — a meta-analysis of 36 studies involving 2,086 participants found a meaningful reduction in high-frequency HRV across anxiety disorders, independent of medication status or disorder subtype.⁷

The low vagal tone that characterizes anxiety is not a consequence of being anxious. It’s part of the underlying neurobiology. It means the autonomic nervous system has shifted toward a default of sympathetic readiness — a sustained low-level threat state — that reduces the capacity for emotional regulation, recovery from stress, and extinction of fear responses.

Depression shows the same pattern. Post-traumatic stress disorder shows it. The vagus nerve is a central component of the emotional regulation circuitry, not a downstream consequence of psychological distress.

Subscribe now

What Is Degrading Your Vagal Tone Right Now

The vagus nerve’s function declines with age. That part is biological and progressive. But the rate of decline, and the baseline level of vagal tone at any age, is substantially determined by modifiable inputs.

• Chronic psychological stress is the most powerful suppressor of vagal tone. Sustained HPA activation from unresolved psychological stress keeps the sympathetic nervous system in a low-level threat posture that actively inhibits parasympathetic function. The vagal brake on the heart and the immune system cannot engage properly when the nervous system is continuously expecting a threat.

• Poor sleep degrades vagal tone through multiple pathways: fragmented sleep architecture impairs overnight autonomic recovery, reduces the parasympathetic restoration that occurs primarily during slow-wave sleep, and elevates cortisol and norepinephrine concentrations that directly suppress vagal activity the following day.

• Alcohol acutely suppresses vagal tone. Even moderate consumption in the evening depresses HRV through the night, reducing the overnight autonomic recovery that should accompany sleep.

• Physical inactivity allows vagal tone to atrophy from disuse, just as muscles atrophy without load. The cardiovascular system’s autonomic flexibility — its capacity for rapid vagal modulation — requires regular aerobic conditioning to maintain. Without it, both resting vagal tone and the speed of vagal recovery after exertion decline progressively.

• Social isolation is a vagal tone input that medicine almost never considers. The polyvagal theory, developed by neuroscientist Stephen Porges, identifies a social engagement system anatomically grounded in the ventral vagal pathway — the branch of the vagus that regulates facial expression, vocal prosody, and orienting toward others. Real social connection, particularly face-to-face interaction, exercises this system. Chronic isolation allows it to downregulate.

• Ultra-processed diet disrupts gut microbial diversity and the vagal signaling that originates in the gut, creating a feedback loop in which poor gut health reduces the quality of afferent vagal input to the brain, further compromising autonomic regulation.

Why This Is Different From Most Biological Aging Processes

Most of the cellular mechanisms underlying aging — mitochondrial decline, telomere erosion, accumulating senescent cells — respond slowly and incompletely to lifestyle interventions. They require years of consistent behavior change to show meaningful movement.

Vagal tone responds in weeks.

Specific breathing protocols change HRV within a single session and produce durable improvement within four weeks. Aerobic exercise produces measurable vagal adaptation within eight weeks. The speed of response is what makes this one of the most clinically tractable targets in the longevity and prevention literature, and what makes having the specific protocol matter so much more than a general recommendation to “reduce stress.”

Below, I’ll share the exact breathing technique that outperformed mindfulness meditation in a Stanford RCT — the specific ratio, duration, and frequency; the exercise protocol with the largest documented effect size for vagal adaptation; the cold water protocol that directly activates the vagal reflex in under 30 seconds; the daily practice that every singer and speaker has been doing accidentally for their entire life; and the HRV biofeedback approach that a 2025 meta-analysis of 18 studies found significantly improved both depression scores and HRV simultaneously.

Read more