Also known as: multi, MVM, multivitamin-mineral
Cheap insurance against gaps you probably do not have — with one recent, genuinely interesting exception for memory in older adults.
Large trials and the USPSTF review find no reduction in cardiovascular disease, cancer, or mortality in well-nourished adults. COSMOS cognitive substudies found a small memory benefit in older adults, but this finding still needs independent replication, which is the main reason this is not a D.
The multivitamin is the most-purchased supplement in the world and one of the least supported, and for years the fair summary was simply "expensive urine". That summary is now slightly too harsh, which makes it more interesting than it used to be.
Start with what has failed. The Physicians' Health Study II, the largest and longest trial of its kind, found no reduction in cardiovascular events over more than a decade. The US Preventive Services Task Force reviewed the whole literature and recommended against multivitamins for preventing cardiovascular disease or cancer in healthy adults. COSMOS, in more than 21,000 people, found no effect on cancer or cardiovascular outcomes. On the headline endpoints, the answer has been consistently no.
The exception came from COSMOS as well. Its cognitive substudies reported a small but replicated improvement in memory in older adults taking a daily multivitamin over one to three years — an effect roughly equivalent to a couple of years of age-related decline, most pronounced in participants with poorer baseline diet quality. It is a modest finding on a secondary endpoint, it needs independent replication, and it is the single most credible piece of evidence the category has produced in decades.
The honest reading is that a multivitamin is insurance rather than treatment. If your diet is varied and adequate, you are paying for nutrients you already have and will excrete. If your diet is genuinely restricted — a persistent deficit, a limited-variety eating pattern, an absorption problem, older age with declining intake — the odds that a low-dose broad formula catches something real go up.
A few practical notes. Avoid megadose formulas: beta-carotene supplementation increased lung cancer in smokers, and high-dose vitamin E has its own unhappy history, so more is not safer. Check the iron: most adult men and postmenopausal women do not need it, and a formula without it is the better default unless a test says otherwise. And treat it as what it is — a hedge, not a substitute for the diet that would have made it unnecessary.
There is no single mechanism — a multivitamin is a broad, low-dose insurance policy against micronutrient shortfalls. Its logic is population-level: correcting a marginal deficiency in someone who has one, while doing nothing for everyone else in the bottle.
Standard-dose formulas are safe. Risk lives in megadose products: beta-carotene raises lung cancer risk in smokers, high-dose vitamin A is teratogenic and bad for bone, and iron is dangerous in overload conditions such as haemochromatosis. Iron-containing tablets are also a leading cause of paediatric poisoning — keep them out of reach.
This guide is educational, not medical advice. Talk to a physician or pharmacist before starting any supplement, especially alongside prescription medication or a medical condition.
Evidence review last updated