Supplements: What a Blood Test Can Tell You

Whether a supplement does anything for you depends mostly on one question: is your body actually missing something? For people without a deficiency, major evidence reviews find no clear benefit from most vitamin and mineral products for preventing heart disease or cancer ¹. But where there is a real gap, targeted supplementation can make a meaningful difference, and a blood test is what reveals that gap.

That is good news. It means nobody has to guess which trend to follow. Your own body can give you the answer.

Why are supplements suddenly everywhere?

Because social media has turned them into a lifestyle. Scroll through Instagram or TikTok and you will find morning routines with five different powders, capsules for "more energy", and promises of better skin, better sleep and sharper focus.

A recent review looked at what this does to adults: people who see a lot of supplement content are more susceptible to marketing and more likely to take products without professional advice, often products with no proven benefit ². The authors call for better health literacy and more conversations between patients and doctors ².

There is something positive underneath this. Many people genuinely want to take charge of their health. The motivation is already there. It just needs pointing in the right direction: away from trends and toward actual needs.

Where does the idea of "individual needs" come from?

The idea is older than many people think. In 1968, Nobel Prize-winning chemist Linus Pauling coined the term "orthomolecular", roughly meaning the right molecules in the right amounts ³. His idea was that every person has their own requirement for certain nutrients, which may not match the average.

On one point, though, Pauling was wrong. He championed very high doses, for example of vitamin C, and that approach has not held up in research. For people without a deficiency, most supplements offer no clear advantage, and some can even cause harm: in studies, beta-carotene increased the risk of lung cancer in people who smoke ¹. Fat-soluble vitamins such as vitamin A can also build up in the body and cause problems at high doses ¹.

What remains of Pauling's idea is its valuable core: every body is different. Modern preventive medicine picks up exactly that thought, with one crucial difference. It does not assume what you need. It measures it.

How does testing help you find what you need?

Testing turns a guess into a decision. A blood test shows whether vitamin D, vitamin B12 or iron, for example, are really low, or whether you can save your money.

It gets really interesting when you test more than once. An analysis of data from a personalised nutrition platform looked at exactly this: more than a thousand healthy adults had their blood tested, received tailored recommendations on diet, exercise and supplements, and were tested again later ⁴. Among people whose values were initially outside the normal range, most markers moved toward normal at the second test ⁴. People with low vitamin D who had chosen a vitamin D supplement improved more often ⁴.

Perhaps the most important idea behind it: only a follow-up test tells you whether a supplement is actually reaching your body. Without one, you cannot know whether you are doing something useful, something unnecessary, or already too much.

Why do your needs change over a lifetime?

Because your body changes. This is best studied in older age, when people often take in too little vitamin D, vitamin B12, folate, zinc, iron or magnesium ⁵.

With vitamin B12, the reason is often not diet at all. To absorb the vitamin from food, the gut needs enough stomach acid, and stomach acid often declines with age ⁵. Vitamin D is similar: the skin produces less of it as we get older, even with the same amount of sun ⁵. So you can eat well and still develop a deficiency.

Other life stages, such as pregnancy or very intense training, can also shift your needs. Those are exactly the times when medical guidance is especially worthwhile.

In everyday terms: a value that was fine five years ago may not be fine today. Testing regularly lets you spot changes early, long before they show up as tiredness or trouble concentrating. Read more in our article Vitamin D: why so many people run low.

What can a blood test tell you, and what can't it?

A blood test is an objective look inside the body. Unlike a food diary, it does not depend on how well you remember what you ate last week ⁵. That is why blood measurements are considered one of the most important ways to assess micronutrient status ⁵.

At the same time, every value is a snapshot. Some nutrients are easy to read in the blood; for others, the blood level says less about how full the body's stores are. That is why experts prefer to look at results in context: alongside diet, lifestyle, symptoms and changes over time ⁵.

This is exactly where repeated testing shines. A single value is a photo; several values make a film. Only over time can you see whether something is improving, holding steady or slowly slipping, and whether a change you made is really doing its job ⁴.

How do you use supplements wisely?

With a simple cycle: test, act in a targeted way, test again.

• Test first, then supplement: a blood test shows whether there is a gap at all.
• Targeted, not scattershot: one product for a confirmed need beats a combination product "for everything" ¹.
• Retest after a few months: this shows whether the change is working and lets you adjust the dose ⁴.
• Listen to your body: energy, sleep and focus are valuable clues, and most meaningful alongside your test results.
• Talk to a doctor: especially for high doses, if you take medication, or if you have a health condition.

What does this mean for the prevention of tomorrow?

The supplement boom shows how much people want to do something for their own health. That is a huge opportunity. The medicine of the future will not hold this back; it will give it a solid foundation, with measurements instead of myths and personal needs instead of one-size-fits-all.

This is not just about individuals. In an ageing society, a great deal depends on whether people spend their extra years healthy and active. A deficiency caught early and corrected in a targeted way is a small but very concrete building block, and one that everyone can take into their own hands.

Perhaps that is the nicest twist in this story. Pauling's vision of individual needs was ahead of its time, and today we finally have the tools to put it into practice responsibly. Not taking more, but understanding better: that is where the real freedom lies.