Do Multivitamins Work? What the Large Trials Actually Show

Nutrition · Published 2026-10-24

Tablets and capsules arranged as a question mark on a plate beside a fork, seen from above — Tablets arranged as a question mark on a plate.

A daily multivitamin is the most common supplement habit in many countries. The question of whether it does anything for people who already eat a reasonable diet has been tested in some unusually large trials. The results are clear enough to summarise in one line, and nuanced enough to need a page.

The short answer

For generally healthy, well-nourished adults, multivitamins have not been shown to prevent heart disease or to extend life, and the evidence on cancer and cognition is limited and mixed. The US Preventive Services Task Force (USPSTF) concluded in 2022 that the evidence is insufficient to assess the balance of benefits and harms of multivitamins for preventing cardiovascular disease or cancer. Multivitamins can still have a place for people with specific needs, discussed at the end of this page.

Physicians' Health Study II

This US trial randomised 14,641 male physicians aged 50 and over to a common daily multivitamin or placebo and followed them for a median of about 11 years.

Cancer: the multivitamin group had a modest 8% reduction in total cancer incidence (hazard ratio 0.92), a result that was statistically significant but borderline (Gaziano et al., JAMA 2012). There was no significant effect on prostate cancer, the most common cancer in the trial, or on cancer deaths.
Cardiovascular disease: no reduction in major cardiovascular events, heart attack, stroke or cardiovascular death (Sesso et al., JAMA 2012).
Cognition: no difference in cognitive decline over about 12 years in a subset of participants.

The participants were male doctors, healthier and better nourished than the general population, which limits how far the findings can be generalised.

COSMOS

The COcoa Supplement and Multivitamin Outcomes Study randomised 21,442 older US adults to a daily multivitamin, cocoa extract, both or placebo for a median of 3.6 years.

Cancer: the multivitamin did not significantly reduce invasive cancer (Sesso et al., American Journal of Clinical Nutrition 2022).
Cardiovascular disease: no significant effect of the multivitamin on cardiovascular events.
Memory and cognition: three cognition substudies (COSMOS-Mind, COSMOS-Web and COSMOS-Clinic) reported small benefits on some measures of global cognition and memory over two to three years, and a pooled analysis published in 2024 supported a modest effect. These are interesting findings, but they come from one trial programme, the effect sizes are small, and their clinical importance is uncertain. They do not show that multivitamins prevent dementia.

Trial	Participants	Follow-up	Main findings for the multivitamin
Physicians' Health Study II	14,641 US male physicians aged 50+	Median about 11 years	8% fewer cancers (HR 0.92, borderline); no effect on cardiovascular events or cognitive decline
COSMOS	21,442 older US adults	Median 3.6 years	No significant effect on invasive cancer or cardiovascular events; small benefits on some memory and cognition measures

Sources: Gaziano et al., JAMA 2012; Sesso et al., JAMA 2012; Sesso et al., Am J Clin Nutr 2022, and the COSMOS cognition substudies (see Sources below).

Observational data on lifespan

Several large cohorts have looked at whether people who take multivitamins live longer. An analysis of about 390,000 US adults from three cohorts, followed for more than 20 years, found that regular multivitamin use was not associated with a lower risk of death; if anything, risk was slightly higher in the early years of follow-up (Loftfield et al., JAMA Network Open 2024). Observational studies cannot prove cause and effect, but the absence of a benefit in such large numbers is consistent with the trials.

When high-dose single nutrients did harm

The history of antioxidant trials explains why authorities are cautious about "more is better":

The Alpha-Tocopherol, Beta-Carotene (ATBC) trial in Finnish male smokers (1994) and the CARET trial in smokers and asbestos-exposed workers (1996) found that beta-carotene supplements increased lung cancer risk.
Based on these and other trials, the USPSTF (2022) recommends against beta-carotene supplements and against vitamin E supplements for preventing cardiovascular disease or cancer.

Typical multivitamins contain amounts close to reference intakes and are not the same as these high-dose single-nutrient interventions, but the lesson is that supplements are biologically active and need to be tested, not assumed to be harmless.

Why the results look like this

Vitamins prevent deficiency diseases. In people who already get enough from their diet, adding more does not usually produce extra benefit, because the body's needs are already met. Most chronic diseases also have many causes that a vitamin pill does not address. The populations in the big trials were largely well nourished, which is exactly the group in which little benefit would be expected.

Who may benefit from a multivitamin or specific supplements

Official guidance targets specific nutrients for specific groups rather than recommending multivitamins for everyone. Examples include folic acid before and in early pregnancy, vitamin D in winter or for people with little sun exposure, vitamin B12 for vegans and many older adults, and nutrients after weight-loss surgery or in malabsorption conditions. For some people a multivitamin is a convenient way to cover several of these, but the choice is best made with a health professional. See who may need supplements.

Points to watch if you do take one: check that you are not doubling up on nutrients from other supplements or fortified foods, avoid vitamin A-containing products in pregnancy unless prescribed, be aware that products with iron are dangerous to young children, and that vitamin K in some multivitamins can affect warfarin. Supplements are regulated as foods in the EU and UK and, in the US, are not approved by the FDA for safety or effectiveness before sale, so label claims are not a guarantee of benefit.

In short

In large trials of healthy adults, multivitamins did not prevent heart disease and did not reduce deaths.
One trial in male doctors found a modest reduction in total cancer; another trial did not.
COSMOS reported small effects on memory tests in older adults; their practical meaning is uncertain.
Targeted supplements for people with specific needs are a different matter from routine multivitamin use.

This page is general information, not medical advice. Talk to a doctor, pharmacist or registered dietitian before starting a supplement, especially if you take medicines, are pregnant or have a long-term condition.

Sources

US Preventive Services Task Force. Vitamin, mineral, and multivitamin supplementation to prevent cardiovascular disease and cancer: recommendation statement. JAMA 2022;327(23):2326–2333.
Gaziano JM et al. Multivitamins in the prevention of cancer in men: the Physicians' Health Study II. JAMA 2012;308(18):1871–1880.
Sesso HD et al. Multivitamin in the prevention of cardiovascular disease in men. JAMA 2012;308(17):1751–1760.
Sesso HD et al. Effect of cocoa flavanol supplementation and a multivitamin on cancer and cardiovascular outcomes (COSMOS). Am J Clin Nutr 2022.
Loftfield E et al. Multivitamin use and mortality risk in 3 prospective US cohorts. JAMA Netw Open 2024.
The ATBC Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. N Engl J Med 1994;330:1029–1035.
NIH Office of Dietary Supplements, Multivitamin/mineral supplements fact sheet.