Are You Buying Supplements You Don’t Really Need?
Part 1: Vitamin D, Magnesium and Omega-3
The phone buzzed at 11:47 pm.
James had been asleep. He was a family doctor who had spent 15 years telling patients to eat their vegetables, reduce the processed foods, come back for another blood test in six months. He knew the script by heart. He was the script.
The notification was from his own health app, syncing results from the private blood panel he had finally got around to booking. Not for any symptom, just curiosity.
He sat up and read the numbers.
Vitamin D: 14 ng/mL. Severely deficient. Below the threshold that triggers a clinical alert.
Omega-3 index: 3.1% — the bottom of what is considered adequate.
He put the phone down and stared at the ceiling for a long time.
The next morning he went back through his diet. Oats with fruit for breakfast. A salad at lunch most days. Grilled chicken or fish most evenings. A handful of almonds as a snack. By any reasonable standard, this was a good diet.
And it was.
The problem was what “eating well” cannot fix: a life lived almost entirely indoors, in a country where meaningful sun exposure is available maybe four months of the year. Soil that is measurably less mineral-rich than it was sixty years ago. A workload that keeps cortisol quietly elevated, burning through magnesium faster than it’s replaced. A fish intake that, if he was honest, was twice a week at best, and not always the fatty kinds.
None of this is unusual. It is, in fact, the situation most health-conscious adults are in without knowing it.1
This post is about the three nutrients most likely to be insufficient even in genuinely good diets. The three nutrients covered here are the most consistently under-supplied in Western diets regardless of diet quality.
Understanding why changes what you do about it.
The One You Almost Certainly Can’t Get From Food
Vitamin D, often referred to as “the sunshine vitamin,” is not technically a vitamin, as the body can synthesize it when exposed to UVB rays from sunlight.
To maintain optimal levels, it’s recommended to spend time in the sun without sunscreen several times a week: about 10 minutes in summer and 20 minutes in winter, preferably early in the morning or late in the afternoon, adjusting the duration based on factors such as skin type, latitude, and season.
This “vitamin” plays a fundamental role in the body. While it’s known for keeping our bones strong, its functions go far beyond that. It’s essential for the proper functioning of the immune system against diseases such as rheumatoid arthritis, lupus, multiple sclerosis, type 1 diabetes, and certain types of cancer.2 Additionally, it reduces chronic inflammation,3 which is associated with most current diseases.
Up to 95% of the United States population has a vitamin D deficiency,4 with levels even higher in many European countries.5
Most people do not get enough UVB year-round to maintain adequate levels. Indoors for most of the day. Clothed in winter. Sunscreen in summer. Darker skin, which reduces synthesis efficiency. Age, which does the same.
Very few foods contain meaningful amounts naturally. Fatty fish, egg yolks, and liver provide some. Fortified products provide variable amounts.
This is why many health authorities formally recommend supplementation from October to March.
Action step: A 25-hydroxyvitamin D blood test gives you your actual level. This single test changes everything about whether you need to supplement, and at what dose. Request it at your next appointment.
The Mineral That Modern Living Drains
This mineral is required for more than 300 biochemical reactions in the body, such as protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. It also supports the functions of many other nutrients, such as vitamin D, being essential for its synthesis, transport, and activation.
Enzymes that repair DNA in our cells require magnesium, making this mineral essential for healthy aging. Its deficiency has been linked to age-related changes in cells and tissues.
The primary magnesium-rich sources include seeds (pumpkin, chia), nuts (almonds, cashews), leafy green vegetables (spinach), legumes, and whole grains. However, achieving optimal magnesium levels through diet alone can be challenging.
The magnesium content in our food has significantly decreased due to soil quality degradation. Industrial agriculture has progressively reduced the magnesium content of crops over the last sixty years.6 A bowl of spinach today contains less magnesium than the same bowl in 1960. Refined grains lose most of their magnesium in processing. Chronic stress elevates cortisol, which increases urinary magnesium loss. Alcohol is a magnesium diuretic.
The body absorbs only 30–40% of the magnesium consumed through food. Additionally, some magnesium-rich foods, such as spinach, contain antinutrients that can hinder absorption. Moreover, magnesium requires vitamin D for proper absorption. Since vitamin D deficiency is common, even those consuming sufficient magnesium may still have a deficiency in this mineral.
NHANES data consistently shows that roughly half of American adults do not meet the estimated average requirement for magnesium from diet alone.7
Since the majority of the body’s magnesium is stored within cells and bones, assessing magnesium status can be challenging. The most frequently used test is the measurement of serum magnesium concentration; however, serum values do not reliably represent total body magnesium stores or magnesium levels in particular tissues. For a more complete evaluation of magnesium status, both laboratory testing and clinical assessment may be needed.
Action step: Before assuming your diet covers magnesium, be honest about how often you actually eat legumes, nuts and seeds, and leafy greens in a typical week. The gap between described diet and actual diet is, in dietary research, consistently large.
The Fat Your Brain and Arteries Are Waiting For
The omega-3 conversation collapses into “eat more fish”, which is correct, but incomplete. The biologically active forms are EPA and DHA, found almost exclusively in fatty fish, shellfish, and algae. Plant-based ALA (flaxseed, walnuts) converts to EPA at less than 10%, and to DHA at less than 1%.8 Eating flaxseed does not substitute for marine omega-3s in any meaningful way.
DHA is a structural component of the brain and retina. EPA is the omega-3 most associated with cardiovascular outcomes. Together they influence triglycerides, blood pressure, platelet function, and inflammation throughout the body.
A 2021 meta-analysis of 63 randomised controlled trials found that omega-3 supplementation significantly reduced triglycerides, blood pressure, and markers of systemic inflammation.9
Dietary surveys find that the median adult in the UK and US consumes far less combined EPA+DHA than the amounts associated with benefit (roughly 250–500 mg/day).10
The problem with the modern diet is that many people consume excessive amounts of omega-6, primarily through ultra-processed products and refined vegetable oils, leading to omega-6:omega-3 ratios as high as 20:1. This imbalance can promote chronic inflammation and contribute to serious health problems such as depression, cancer, cardiovascular diseases, asthma, rheumatoid arthritis, and even an increased risk of premature death.11
The omega-3 index, which reflects the percentage of EPA and DHA in red blood cells, is a vital indicator of longevity. Remarkably, each 1% increase in this index is linked to a 20% reduction in the risk of dying from all causes.12 Prioritizing omega-3 intake could significantly enhance your lifespan and overall health.
Action step: Two to four portions of fatty fish per week — salmon, sardines, mackerel, herring — meets most people’s EPA+DHA needs. If that is not realistic for you consistently, this is the gap most likely worth supplementing.
The Honest Answer
It depends on the specific nutrient, your specific diet, your circumstances, and your actual blood levels. For the three micronutrients covered here, the evidence says that diet alone, even a good one, frequently falls short.
Below, I’ll share a downloadable guide outlining which supplements are worth buying, which forms matter, exact dosing based on your blood results, what to skip, and a 90-day protocol to put it all into action.