Vitamins and multivitamins.

Deficiency and prevention are different questions

Replacing a deficiency asks whether intake or absorption is inadequate and whether replacement corrects a measurable problem. Preventive claims ask whether taking a supplement changes future disease or survival. Evidence for the first question cannot be used as proof of the second. For product-specific storage questions, see storing vitamins and minerals. For an example involving infections, see vitamin A and immunity.1

Illustrations

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Multivitamins are not one standard product

There is no single multivitamin formula. Products differ in nutrients, doses and forms, and labels may be designed for different ages or life stages. Compare the full Supplement Facts panel rather than relying on the product name.13

Can a multivitamin improve memory?

There is an encouraging but limited signal from a large trial; it does not establish that multivitamins prevent dementia. COSMOS-Web randomly assigned 3,960 older US adults to a particular multivitamin or placebo; 3,562 had a baseline and at least one follow-up assessment and were included in the reported analysis. On a 20-word immediate-recall test, the estimated difference in improvement after one year was 0.23 words in favour of the multivitamin group on average. Both groups improved, and a group average this small does not mean each person noticed a difference. There was no statistically significant improvement on the study’s other tests of memory retention, object recognition or executive function. The online-test participants were predominantly non-Hispanic White; results may not apply equally to other populations or formulas. Investigators estimated an age-equivalent comparison from cross-sectional data, but the trial did not show that anyone became years younger or avoided dementia. Funding included NIH and Mars Edge; Pfizer Consumer Healthcare, now Haleon, helped supply pills and packaging. Authors said funders did not direct the study or analysis. Memory changes have many causes, including some treatable deficiencies; see vitamin B12 and deficiency and seek clinical assessment for concerns.5

Do multivitamins prevent cancer?

In the Physicians’ Health Study II, 14,641 male US physicians aged 50 or older were randomly assigned a specific multivitamin or placebo. After a median of 11.2 years, the multivitamin group had a modestly lower rate of total cancer: 17.0 versus 18.3 diagnoses per 1,000 person-years, a measure that accounts for time followed. Some participants had previously had cancer. The trial tested one product in a particular population; it does not establish prevention of every cancer or benefit for everyone. NIH and supplement companies supported the study, and the multivitamin was supplied by its manufacturer.

A 2022 US Preventive Services Task Force recommendation judged the overall evidence insufficient to assess the balance of benefits and harms of multivitamins for preventing cancer or cardiovascular disease in the general adult population it considered. That question is different from correcting a deficiency or a specific pregnancy-related need.68

Do multivitamins help people live longer?

A 2024 observational analysis followed 390,124 US adults in three cohorts. Reported multivitamin use was not associated with a mortality benefit. Unlike a randomized trial, the study did not assign products: differences in health, diet, healthcare access or reasons for taking supplements can influence the comparison despite statistical adjustment. It does not prove supplements shorten life, nor does it exclude benefits for people with a specific deficiency or prove every formulation has the same effect.7

More can be harmful

Some vitamins and minerals accumulate or interfere with medicines. Interactions can matter with anticoagulants, thyroid medicines and other treatments; excess doses can cause toxicity. Pregnancy, childhood, kidney disease, surgery and diagnosed deficiencies warrant particular care from a qualified professional.342

A proportionate conclusion

A varied diet is the main source of nutrients for most people. A supplement may be useful for a specific reason, but a general claim that a multivitamin prevents chronic disease remains stronger than the broad evidence supports. Product quality and the actual ingredient list still need checking. Explore the individual B vitamins: B1, B2, B3, B5, B6, biotin (B7), folate (B9) and B12. For a familiar claim, see vitamin C and colds. For form-specific benefits and risks, see vitamin A and beta-carotene.12