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MYTH BUSTED · SUPPLEMENT MYTHS · 10 MIN READ
The Dose Is The Whole Story — And Some Of The Largest Trials Ever Run On This Were Stopped Early
Most of what’s in your supplement drawer isn’t making you healthier. Some of it is doing nothing at all — and a couple of things, on the evidence, are mildly counterproductive.
The Short Version
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A vitamin isn’t good or bad — a dose is. Below the right range you get deficiency. Above it, for several vitamins, you get a different set of problems entirely, and some accumulate silently for years.
The idea that more vitamins equals more health is not ancient folk wisdom. It has an author, a publication date, and a single spectacularly credentialed source: Linus Pauling, the only person in history to win two unshared Nobel Prizes — Chemistry in 1954, Peace in 1962. There was, on paper, nobody more qualified to be believed.
In 1970 he published Vitamin C and the Common Cold, built on very little beyond anecdote, and over the following years escalated the claims: that megadoses of vitamin C could address heart disease, leprosy, and eventually cancer. When the scientific community pushed back in peer-reviewed journals, he did not answer them there — he went directly to the public, where his two Nobel Prizes did the arguing for him.
It worked completely. The book was a bestseller, the modern supplement industry took the shape it still has, and half a century later people who have never heard his name are still repeating his hypothesis in pharmacy aisles. Pauling died of prostate cancer in 1994. The trials that followed his death did not vindicate him — and in some cases found the opposite of what he had promised.
Here is what makes this myth genuinely unusual: it is not simply unsupported. It has been tested, at enormous scale, by people who expected it to be true — and the results were bad enough that ethics boards shut the studies down.
The reasoning going in was sound. Antioxidants neutralise free radicals; free radicals are implicated in cancer; therefore antioxidant supplements should reduce cancer. It is a clean hypothesis. It is also, when actually tested in humans at supplemental doses, wrong.
CARET · 1996
18,314 people at high risk of lung cancer, given beta-carotene and vitamin A. The trial was halted early: 28% more lung cancers and 17% more deaths in the supplement group. Published in the New England Journal of Medicine.
SELECT · 2011
Vitamin E was expected to reduce prostate cancer. It was associated with a 17% increase instead — 76 cases per 1,000 men against 65 on placebo. Published in JAMA.
The Finnish ATBC study found the same pattern independently: 18% more lung cancers among smokers taking beta-carotene. By 2022 the US Preventive Services Task Force had reviewed everything available and issued a formal recommendation against beta-carotene supplementation for preventing cancer or heart disease. Not ‘insufficient evidence’ — a recommendation against.
A vitamin is not good or bad. A dose is. Below the range, deficiency. Above it, a different set of problems.
In 1913, two men were dragging sledges across Antarctica after losing most of their supplies down a crevasse. Douglas Mawson and Xavier Mertz survived by eating their remaining sled dogs. Mertz found the meat too tough and stringy, so he took the softer portion instead — the liver.
Husky liver, like polar bear and seal liver, stores extraordinary concentrations of vitamin A. Roughly 100g of it delivers a toxic dose for an adult. Mertz’s skin peeled away in sheets, he became delirious, and he died. Mawson, who ate less of it, lost the soles of his feet but survived to walk out alone. Vitamin A was not discovered until 1917, four years later.
This is the mechanism, in its most extreme form. Vitamins A, D, E and K are fat-soluble — they dissolve in fat and are stored in the liver and adipose tissue rather than flushed out in urine. They accumulate.
Nobody is eating husky liver in Manchester. But the same principle operates quietly at supplement doses over years, which is precisely why it is so easy to miss — there is no acute signal that you have taken too much. You simply keep topping up a store that has nowhere to drain.
The reassurance that you simply urinate out the excess is only half true. Vitamin B6 is the clearest counter-example: sustained high intake causes peripheral neuropathy — tingling, burning and numbness that can progress. Cases occurred at doses under 50mg, with no reliably safe threshold identified.
B12 deficiency produces anaemia (visible on a blood test) and nerve damage (which isn’t). High folic acid intake can correct the anaemia while leaving the deficiency untouched — removing the visible warning sign while neurological damage continues underneath.
High-dose calcium meaningfully reduces iron absorption — which matters enormously for active women. Excess zinc depletes copper over time. Take a big multivitamin and you’re not adding five benefits; you’re running five interactions.
Supplements are regulated as foods, not medicines — no pre-market approval, no requirement to demonstrate efficacy or dose accuracy before sale. Check for independent third-party testing certification, and be sceptical of proprietary blends that decline to state doses.
Vitamin D is the exception. At UK latitude, skin synthesis is effectively switched off between October and March, regardless of time spent outside — which is why it has genuine population-level backing here, at a modest 10mcg a day.
The evidence-based approach is unglamorous and can be written in four words: test first, then supplement. Identify the specific gap, correct that gap, leave everything else to food. Broad-spectrum supplementation in healthy adults eating a varied diet has repeatedly failed to demonstrate the benefits it promises.
The Short List For Active Women In The UK
Vitamin D — 10mcg daily, October to March. Year-round if you train indoors or cover up outdoors. Standard UK public health advice, not a supplement-industry claim.
Iron — only if blood work confirms deficiency. Its symptoms — fatigue, breathlessness, flat performance — are almost identical to overtraining, which is exactly why guessing is a poor strategy in both directions.
Magnesium — glycinate in the evening, if sleep quality or cramping is genuinely a problem. Cheap, low-risk, reasonable evidence for exactly those two things and not much else.
Everything else — the greens powders, the immunity blends, the 400% RDA multivitamin — should have to earn its place with a blood test, not with packaging. And if you are pregnant, managing a medical condition, or taking prescription medication, this conversation belongs with your GP rather than with a website.
Micronutrients work inside a range. Below it you get deficiency; above it you get a different set of problems, and in the case of the fat-soluble vitamins those problems accumulate silently over years. That is not a fringe position — it is why CARET was stopped early and why the USPSTF recommends against beta-carotene outright.
The belief that more must be better was authored by one brilliant man in 1970 who skipped peer review and went straight to the public. It has been tested since, thoroughly, in tens of thousands of people. It did not hold up.
Get blood work. Fix what is actually missing. Eat properly, and put the money you were spending on a drawer full of tubs into food you will genuinely enjoy. Guesswork is not a nutritional strategy — it is just an expensive habit with good graphic design.
Guesswork is not a nutritional strategy.
TEST.
Omenn GS et al. (1996). Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease (CARET). New England Journal of Medicine, 334(18).
ATBC Cancer Prevention Study Group. Beta-carotene supplementation and lung cancer incidence in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study.
Klein EA et al. (2011). Vitamin E and the risk of prostate cancer: the SELECT trial. JAMA, 306(14).
US Preventive Services Task Force (2022). Vitamin, mineral, and multivitamin supplementation to prevent cardiovascular disease and cancer: recommendation statement. JAMA.
Pharmacy Times (2025). Understanding the toxicity profiles of fat-soluble vitamins: insights into vitamins A, D, E and K.
PMC (2025). Toxic effects of excess vitamins A, B6 and folic acid on the nervous system.
EFSA NDA Panel (2023). Scientific opinion on the tolerable upper intake level for vitamin B6.
Miller JW et al. (2024). Excess folic acid and vitamin B12 deficiency: clinical implications? Food and Nutrition Bulletin.
Mawson & Mertz — Medical Journal of Australia (2005). A re-evaluation of their ill-fated mapping journey during the 1911–1914 Australasian Antarctic Expedition, 183(11).
This page is educational and is not medical advice. If you have a health condition, are pregnant or breastfeeding, or take prescription medication, speak to your GP before changing your supplement routine.
Is it true that taking more vitamins is always healthier?
No. Micronutrients work within a range — too little causes deficiency, too much causes a different set of problems. Several large trials testing high-dose antioxidant vitamins were stopped early because participants taking them did worse, not better.
Where did the 'more vitamins is better' idea come from?
Largely from Linus Pauling, a two-time Nobel laureate who published Vitamin C and the Common Cold in 1970 and took his megadose claims directly to the public rather than through peer review. The idea took hold before it was properly tested.
Can vitamins actually be dangerous?
Yes, particularly the fat-soluble ones (A, D, E, K), which accumulate in the body rather than being flushed out. Vitamin A toxicity is well documented, and there's no acute warning sign that you've taken too much of a fat-soluble vitamin over time.
Which vitamins are actually worth taking in the UK?
Vitamin D has genuine population-level backing, particularly October to March, since UK sunlight isn't strong enough to trigger skin synthesis in winter. Iron and magnesium may help specific people, but ideally after blood work confirms an actual gap.
Is it better to get vitamins from food or supplements?
For most people eating a varied diet, food is the safer default — nutrients arrive in the ratios your body evolved alongside, without the risk of one nutrient interfering with another's absorption, which happens more easily with concentrated supplements.