Evidence Files

Multivitamins: Two Giant Trials, No Protection for Your Heart — and One Surprise About Memory

Two randomised trials followed more than 36,000 people taking a daily multivitamin or a placebo, one of them for over a decade. Heart attacks, strokes, deaths: no difference. A study of 390,124 adults followed for up to 27 years found no survival benefit either. And yet the most interesting result in the field is a positive one — just not where the label points.

Published: 30 September 2026

Verdict

TRICK (weak evidence)

We searched PubMed and Cochrane Library for multivitamin supplementation in healthy adults. There is no shortage of evidence: 211 records tagged as randomised trials with multivitamins in the title, including two of the largest supplement trials ever run. For the reasons most people take them — heart, cancer, living longer — the results are null or marginal, and the US Preventive Services Task Force rates the evidence insufficient to recommend them. The one consistent positive signal is a small memory benefit in older adults, and it comes from a single trial programme.

Why Europe keeps taking them

The multivitamin is the default supplement — the one people take without having a specific reason, as a kind of nutritional insurance. In the US, 31% of adults report using one, and the most common reason given is not treating anything in particular but “overall health and wellness” and filling gaps in the diet.

In Europe the packaging tells you why it feels justified. Under Regulation (EU) No 432/2012, vitamin C, vitamin D, vitamin B6 and zinc may each be labelled as contributing “to the normal function of the immune system”, and eight nutrients — among them iron, folate, vitamin B12 and vitamin C — may claim to contribute “to the reduction of tiredness and fatigue”. A single multivitamin box can carry several of these sentences at once.

Every one of those claims is true, and almost none of them answers the question the buyer is asking. They describe what the nutrient does in the body — which is why deficiency makes you ill. They say nothing about whether adding more on top of an adequate diet makes you healthier. That second question is the one the big trials were designed to test.

What the science actually says

Multivitamins are unusual among supplements: they have been tested in very large, long, independently funded, placebo-controlled trials. The results are clearer than for almost anything else on the shelf.

Heart disease: nothing, after eleven years. The Physicians’ Health Study II randomised 14,641 US male doctors to a daily multivitamin or placebo and followed them for a median of 11.2 years. Major cardiovascular events: 11.0 versus 10.8 per 1,000 person-years (HR 1.01). No effect on heart attack, stroke or cardiovascular death, and no significant effect on total mortality
Cancer: a small signal that did not replicate. The same trial found a modest reduction in total cancer — 17.0 versus 18.3 cases per 1,000 person-years (HR 0.92), with an upper confidence limit of 0.998, as close to the line as a significant result can get. The later COSMOS trial, with 21,442 older adults, found no effect on total invasive cancer (HR 0.97), nor on cardiovascular disease or all-cause mortality. It did see fewer lung cancers (HR 0.62), but that was one of several secondary outcomes
The official verdict: insufficient. The evidence review for the US Preventive Services Task Force pooled 84 studies. For multivitamins it found a small benefit for cancer incidence, with an absolute risk difference of 0.2% to 1.2% in adequately powered trials, and important limitations. The Task Force concluded that the evidence is insufficient to weigh benefits against harms for preventing heart disease or cancer
Living longer: if anything, the opposite direction. A 2024 analysis of three US cohorts followed 390,124 adults with no history of cancer or other chronic disease for up to 27 years. Daily multivitamin users did not live longer; in the first half of follow-up their mortality risk was 4% higher (HR 1.04). Observational data cannot prove harm, but they make a large hidden benefit that the trials somehow missed very unlikely
Memory: the genuine surprise. Three cognitive sub-studies of COSMOS all found small benefits. In COSMOS-Mind, 2,262 older adults assessed by telephone showed better global cognition after three years on a multivitamin. In COSMOS-Web, 3,562 participants recalled more words at one year — an effect the authors equate to about 3.1 years of age-related memory change. A pooled analysis of all three put the global effect at 0.07 standard deviations, which the authors equate to about two years of cognitive ageing
Why the memory result is not yet a treatment. The effect is small in absolute terms (0.07 SD), measured on test scores rather than dementia diagnoses, and all three studies come from the same trial with the same product and the same population — overwhelmingly older and 89% non-Hispanic white in COSMOS-Mind. The authors themselves call for confirmation in a more diverse cohort. It is a promising result, not an established one

Marketing claim vs. evidence

What the box says

"Supports immune function." "Reduces tiredness and fatigue." "Complete nutritional support." The implication is that a daily tablet makes a healthy person healthier — more resilient, more energetic, better protected in the long run.

What the research shows

The immune and fatigue claims are authorised physiology, not trial results. In healthy people, eleven years of daily use did not change heart attacks, strokes or mortality; the cancer benefit did not replicate. The one promising finding — memory in older adults — is not on most labels at all.

Frequently asked questions

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Is it worth taking a multivitamin every day?

For preventing heart disease, cancer or early death in healthy adults, the evidence says probably not. The two largest trials found no effect on cardiovascular events and no effect on total cancer in the more recent one, and the US Task Force rates the evidence insufficient. People with a diagnosed deficiency, or specific needs such as pregnancy, are a different question.

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Do multivitamins help you live longer?

No trial has shown it, and a cohort of 390,124 adults followed for up to 27 years found no survival benefit — daily users had a slightly higher mortality risk in the first half of follow-up (HR 1.04). Neither PHS II nor COSMOS found a significant effect on all-cause mortality.

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Do multivitamins improve memory?

In older adults, possibly a little. Three COSMOS sub-studies found small benefits, and a pooled analysis estimated an effect equivalent to about two years of cognitive ageing. The effect is small, measured on test scores, and all the data come from one trial of one product, so it needs independent confirmation.

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Do multivitamins prevent cancer?

The evidence is mixed. PHS II found an 8% reduction in total cancer in male doctors after 11 years, only just statistically significant. COSMOS found no effect on total cancer. The Task Force review put the absolute benefit at 0.2% to 1.2% and still judged the evidence insufficient.

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Can multivitamins be harmful?

A standard multivitamin at normal doses appears safe — COSMOS reported no safety concerns. Some single high-dose supplements are another matter: the Task Force review found beta carotene increased lung cancer risk in people at high risk, and limited evidence linking vitamin A to hip fracture and vitamin E to haemorrhagic stroke.

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What does “contributes to the normal function of the immune system” mean on a label?

It is an EU-authorised health claim under Regulation 432/2012, permitted for vitamin C, vitamin D, vitamin B6 and zinc when the product is at least a “source” of the nutrient. It describes the nutrient’s normal role in the body. It is not evidence that taking extra strengthens the immune system of someone who is not deficient.

Our Conclusion

The multivitamin is one of the best-tested supplements in existence, and that is exactly why the verdict is clear. For the things most people take it for — a healthier heart, less cancer, a longer life — two very large placebo-controlled trials and a cohort of nearly 400,000 people found no meaningful benefit. The single positive cancer result did not replicate. The label claims about immunity and tiredness are true descriptions of physiology, not evidence that extra helps. The honest complication is memory. COSMOS found a small, consistent benefit on cognitive tests in older adults, and it deserves to be taken seriously — as a hypothesis awaiting independent confirmation, not as a reason to buy. The question worth asking before paying for a daily tablet is not “is this good for me?” but “do I have a deficiency, or a specific need, that a blood test or a doctor has actually identified?” If the answer is no, the best-quality evidence says the money is better spent on food.

Sources

Every claim in the text is linked to a primary source. Links go to the publisher's site, to EUR-Lex, or to PubMed, the US National Library of Medicine database.

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This article is for informational purposes only and does not constitute medical advice. Trick or Treatment analyses the presence of clinical studies in open scientific databases — PubMed and Cochrane Library. The absence of studies in these databases does not automatically mean a drug is ineffective, but it does mean its effectiveness has not been confirmed by evidence-based medicine standards. Any treatment decisions should be made together with your doctor.