Multivitamins: what large trials have shown

Multivitamins have been tested in randomized trials involving tens of thousands of people—a rare case in nutrition where we have experiments with placebos rather than just observations. The results are more modest than advertising suggests and more interesting than a simple "it doesn't work": for some outcomes, there is no effect at all, while for others, there is an effect, but it is small.

A trial of 14,641 doctors

The most well-known study is the Physicians’ Health Study II, where male doctors took a multivitamin or a placebo daily for over a decade.

Regarding cancer outcomes: over a median of 11.2 years, 2,669 cases of cancer were recorded. In the multivitamin group, the incidence was 17.0 versus 18.3 cases per 1,000 person-years—a hazard ratio of 0.92 with a confidence interval of 0.86–0.998 and p = 0.04. Formally significant, but marginal in magnitude.

Regarding cardiovascular outcomes in the same study, there were no differences between the groups.

This is the key detail: in the same trial, one outcome showed a minimal effect, while the second showed none at all.

What the preventive services task force recommends

In 2022, the U.S. Preventive Services Task Force published a recommendation on vitamin and mineral supplements for the prevention of cardiovascular disease and cancer. The conclusion on multivitamins: there is insufficient evidence to assess the benefits and harms.

Two substances were specifically highlighted as those that should not be taken for this purpose: beta-carotene and vitamin E. The basis for beta-carotene is not a lack of benefit, but direct harm: in trials involving smokers, it increased the risk of lung cancer.

This leads to a rule that is more important than any list: "taking vitamins just in case" is not a neutral decision, as some of them have measured harms.

Where an effect was actually found

The COSMOS-Mind study: 2,262 participants with an average age of 73, taking a daily multivitamin or placebo. Cocoa extract did not affect cognitive function, but the multivitamin provided a statistically significant improvement in overall cognitive assessment—0.07 standard deviations with a confidence interval of 0.02–0.12.

The magnitude of the effect is small and was observed in elderly people. There is no basis for extrapolating this to a thirty-year-old person without deficiencies.

Who actually needs supplements

Multivitamins as a "just in case" measure and vitamins taken for specific indications are different things. The latter is prescribed by a doctor for very specific reasons:

• a deficiency confirmed by lab tests;
• pregnancy and planning for pregnancy—as prescribed by a doctor;
• a vegan diet—primarily vitamin B12;
• conditions following gastrointestinal surgery and diseases involving malabsorption;
• a restricted diet for medical reasons.

For individual nutrients that have their own specific contexts, see our materials on vitamin D, magnesium, iron and ferritin, and iodine.

What is important to understand about supplements themselves

Multivitamins are sold as dietary supplements, not as drugs: the legal difference is analyzed in our material on supplements, vitamins, and drugs. A practical consequence is that the composition and dosages are verified by the manufacturer, which is another reason not to exceed recommended amounts on your own.

And finally, something often lost in debates: the trials tested supplements in people who generally eat a regular diet. None of them showed that a pill replaces a diet—they tested whether it adds anything on top of it.

Count it from a photo

Frequently asked questions

Are there any benefits to multivitamins?

In the Physicians’ Health Study II, taking a multivitamin reduced the overall incidence of cancer at the border of significance (hazard ratio 0.92) and did not affect cardiovascular outcomes. The U.S. Preventive Services Task Force in 2022 deemed the evidence insufficient to assess benefits and harms.

Which vitamins should not be taken for prevention?

Beta-carotene and vitamin E: the 2022 USPSTF recommendations explicitly advise against taking them for the prevention of cardiovascular disease and cancer, and beta-carotene trials have shown an increased risk of lung cancer in smokers.

Do multivitamins improve memory?

In the COSMOS-Mind study of people with an average age of 73, a multivitamin provided a small improvement in overall cognitive assessment (0.07 standard deviation). The effect is small and was observed in older participants.

Who actually needs multivitamins?

Those with a confirmed deficiency or a condition that impairs absorption, as well as during pregnancy and on a vegan diet — in all cases, as prescribed by a doctor, rather than "just in case".

Can vegetables be replaced by vitamins from a jar?

Trials have not tested this: in all of them, the supplement was taken in addition to a normal diet, not instead of it.

Read next

• How dietary supplements differ from vitamins and medications — In a pharmacy, two packages of vitamin D sit on the same shelf.
• Vitamin D: how much you need, where to get it, and when to get tested — Vitamin D differs from other vitamins in that humans can produce it themselves—in the skin under ultraviolet light.
• The "optimization" lab panel: what happens when you test for everything — The logic of "measure first, intervene later" seems flawless and is therefore rarely questioned.

This article is for general information. It is not medical advice, a diagnosis, or a prescription for treatment or a diet, and it does not replace a consultation with your doctor. If you have a health condition, are pregnant, take medication, or follow a diet prescribed to you, decisions about food belong with your doctor.

Figures from regulations, guidelines and studies are given as they stood when this article was prepared and may since have changed; check them against the primary sources. This article is not advertising, an offer, or individual advice, and neither the author nor the site owner is responsible for decisions taken on the basis of it.