Should you take a multivitamin?

A multivitamin bundles many vitamins and minerals, each near the recommended daily amount. It is meant to fill gaps, not to act like a drug, so it works best where gaps are real.

Gaps are common. In a nationally representative US survey of 15,030 people, about 31% were at risk of at least one vitamin deficiency or anemia. Risk was 14% among users of full-spectrum multivitamins and 40% among non-users¹⁰. That comparison cannot prove cause, because people who take supplements differ in other ways.

Food still does most of the work. In a cohort of 30,899 US adults, adequate intake of vitamin A, vitamin K, magnesium, zinc and copper went with lower death rates, but only when the nutrients came from food, not from pills¹.

Who clearly benefits

• Pregnancy or planning one. Folic acid, alone or inside a multivitamin, prevents neural tube defects (relative risk 0.31 across five trials), with similar results at 400 micrograms and above². Choose a prenatal formula and avoid more than 10,000 IU of preformed vitamin A a day⁴.
• Diets with no animal foods. Researchers found B12 depletion or deficiency in vegetarians regardless of age or diet type³. See our vitamin B12 page.
• Older adults may get a small memory benefit. Pooled data from three COSMOS substudies showed slightly better memory and overall thinking scores⁸, though an earlier trial in male doctors found none⁹.

What to look for if you buy one

• A plain once-daily formula near 100% of daily values. Avoid megadose products and extra beta-carotene or vitamin E⁵.
• A third-party testing seal. Our guide to telling if a supplement is pure explains what the seals mean.
• Take it with a meal. Spacing rules for iron, calcium and thyroid medicine are in our supplement timing guide.

Physicians' Health Study II

The longest trial of a multivitamin randomized 14,641 male US physicians aged 50 or older (mean age 64.3) to a daily multivitamin or placebo and followed them for a median of 11.2 years. Total cancer was modestly lower with the multivitamin: 17.0 versus 18.3 events per 1,000 person-years (hazard ratio 0.92, 95% CI 0.86 to 0.998). That barely cleared the threshold for statistical significance, and there was no effect on prostate cancer (HR 0.98) or colorectal cancer (HR 0.89, not significant)¹¹.

In the same men, a multivitamin did not change major cardiovascular events (HR 1.01, 95% CI 0.91 to 1.10), heart attack (HR 0.93), stroke (HR 1.06), cardiovascular death (HR 0.95) or total mortality (HR 0.94, 95% CI 0.88 to 1.02)⁶. A cognitive substudy of 5,947 men aged 65 or older, tested by telephone up to four times over 12 years, found no difference between groups (global score change -0.01 standard units, 95% CI -0.04 to 0.02). The authors noted that the doses may have been too low, or the men too well nourished, to benefit⁹.

COSMOS

COSMOS randomized 21,442 US adults (12,666 women aged 65 or older and 8,776 men aged 60 or older) in a two-by-two design with cocoa extract. Over a median of 3.6 years, the multivitamin did not significantly change invasive cancer (HR 0.97, 95% CI 0.86 to 1.09), cardiovascular disease (HR 0.98, 0.86 to 1.12) or all-cause mortality (HR 0.93, 0.81 to 1.08). Lung cancer was lower (HR 0.62, 0.42 to 0.92), but that was one of several site-specific secondary outcomes and needs confirmation. No safety concerns emerged⁷.

Memory and thinking

Pooling three non-overlapping COSMOS cognitive substudies (573 + 2,158 + 2,472 participants), the multivitamin improved global cognition by 0.07 standard units (95% CI 0.03 to 0.11) and episodic memory by 0.06 (0.03 to 0.10), which the authors equated with about two years less cognitive aging. In the in-person clinic substudy alone, the global gain (0.06, 95% CI -0.003 to 0.13) was not significant, although memory was (0.12, 0.002 to 0.23)⁸. The effects are small, follow-up was two to three years, and the male-only PHS II trial found nothing⁹. This is a promising signal, not a reason by itself to start a multivitamin.

Observational data

Loftfield and colleagues pooled three US cohorts (390,124 adults, 164,762 deaths, up to 27 years of follow-up) and tried to account for healthy-user bias and for people starting vitamins when ill. Multivitamin use was not linked to lower mortality: HR 1.04 (1.02 to 1.07) in the first half of follow-up and 1.04 (0.99 to 1.08) in the second¹². In NHANES data linked to deaths (30,899 adults, median 6.1 years), supplement use showed no mortality benefit, and calcium supplements of 1,000 mg a day or more went with higher cancer mortality (rate ratio 1.53, 95% CI 1.04 to 2.25)¹. Both are observational and can be confounded.

Specific groups

A Cochrane review of folic acid before and early in pregnancy pooled five trials in 7,391 women. Neural tube defects fell (relative risk 0.31, 95% CI 0.17 to 0.58; high-quality evidence) and so did recurrences (RR 0.34, 0.18 to 0.64), with no clear effect on other birth defects. Only one of the five trials had a low risk of bias². A cohort of 22,748 pregnant women found that more than 10,000 IU a day of supplemental preformed vitamin A carried a prevalence ratio of 4.8 (95% CI 2.2 to 10.5) for defects arising from the cranial neural crest; the authors estimated that about 1 infant in 57 born to those users had a malformation attributable to the supplement⁴. A review of 18 studies found B12 depletion or deficiency in vegetarians of all ages, with rates from 11% to 90% among older vegetarians³.

Where the evidence disagrees

The two large trials disagree on cancer (slightly lower in PHS II, no difference in COSMOS) and on thinking skills (nothing in PHS II, a small gain in COSMOS). Age, sex, length of follow-up and baseline nutrition differ between them, so neither is a clean test of the other^11,7. The Task Force's 2022 review judged the evidence for multivitamins insufficient (an "I statement") and recommended against beta-carotene and vitamin E; it predates the pooled COSMOS cognition analysis^5,8. The nutrient-gap data are the best argument for "insurance" use, but they are associations¹⁰, and the large trials did not target people with documented deficiencies, so they say little about whether closing real gaps helps^6,7.

Bottom line (confidence 4 of 5). In well-nourished adults a multivitamin neither prevents heart disease or early death nor does much harm; cancer and memory findings are small and inconsistent. For pregnancy planning and for diets lacking B12 the case is strong. Food first, a plain formula second.