Multivitamins
The most widely used supplement. Large trials mostly show no effect on heart disease or cancer, with a small, newer signal for memory in older adults.
Not medical advice. Talk to a doctor before starting if you're pregnant or planning to be, take a blood thinner like warfarin, or take other supplements that could stack with a multivitamin's nutrients.
How It Works
A multivitamin (or multivitamin-mineral, "MVM") combines several vitamins and minerals in one product. Per the NIH Office of Dietary Supplements, there's no standard or regulatory definition of what a multivitamin must contain or in what amounts, so products vary widely. The basic type NIH describes is a once-daily product with most nutrients at or below the Daily Value.
The core use is filling nutrient gaps in the diet. That's a different claim from preventing chronic disease, and the evidence for the two is very different. Multivitamins are very common. In national survey data cited by the U.S. Preventive Services Task Force, 31% of U.S. adults reported using a multivitamin-mineral supplement in the past 30 days.
The Research
Heart disease and cancer (mostly no effect): the U.S. Preventive Services Task Force's 2022 review concluded that the evidence is "insufficient to assess the balance of benefits and harms" of multivitamins for preventing cardiovascular disease or cancer. It's not a recommendation for or against. The same review recommended against beta-carotene and vitamin E supplements for this purpose.
Read the USPSTF recommendation →
The largest long-term trial was the Physicians' Health Study II, which followed 14,641 male U.S. physicians aged 50+ for a median of 11.2 years. A daily multivitamin had no effect on major cardiovascular events (Sesso et al., JAMA, 2012). It led to a modest 8% reduction in total cancer, but no significant effect on cancer deaths or on prostate, colorectal, or other specific cancers (Gaziano et al., JAMA, 2012).
Read the cardiovascular results →
Read the cancer results →
The more recent COSMOS trial (21,442 U.S. adults aged 60+, median 3.6 years) found no significant effect on total invasive cancer, cardiovascular disease, or all-cause mortality (Sesso et al., American Journal of Clinical Nutrition, 2022).
Read the COSMOS trial →
Mortality (observational): a National Cancer Institute analysis of 390,124 generally healthy U.S. adults followed for up to 27 years found multivitamin use was not associated with lower risk of death (Loftfield et al., JAMA Network Open, 2024).
Read the study →
Memory in older adults (newer, small effect): a meta-analysis of three cognition substudies within COSMOS (about 5,200 adults aged 60+) found a daily multivitamin modestly improved global cognition and episodic memory compared with placebo. The authors estimated the effect as equivalent to about 2 years less cognitive aging (Vyas et al., American Journal of Clinical Nutrition, 2024). This is a genuinely positive randomized result, but all three substudies come from the same trial, and the effect sizes were small.
Read the meta-analysis →
Who Might Have a Real Gap
The case for a multivitamin is strongest for specific life stages and diets where a nutrient gap is common, per the NIH Office of Dietary Supplements fact sheet:
Anyone who could become pregnant: the CDC recommends 400 mcg/day of folic acid from fortified foods, supplements, or both, and the USPSTF advises a supplement providing 400–800 mcg/day for those planning or capable of pregnancy, to reduce the risk of neural tube defects. During pregnancy, most providers recommend a prenatal multivitamin.
Adults over 50: the Food and Nutrition Board advises getting vitamin B12 mainly from fortified foods or supplements. Absorption of the B12 naturally found in food tends to decline with age. Some medications, such as proton pump inhibitors, can also reduce it.
Vegetarian and vegan diets: the Dietary Guidelines for Americans suggests people following these diets during pregnancy ask their provider about iron, vitamin B12, and other nutrients. See our Plant-Based & Vegan Diets page for more.
For most other healthy adults eating a varied diet, the trial evidence above suggests a multivitamin is unlikely to change long-term disease risk. It's more of a nutritional backstop than a prevention tool.
Typical Dosing
There's no standard multivitamin dose, since every product has a different formula. The basic type described in the NIH fact sheet is taken once a day and provides most nutrients at or below 100% of the Daily Value. The NIH fact sheet also suggests choosing a product designed for your age, sex, and life stage. For example, 50+ formulas often contain little or no iron and more calcium, vitamin D, and B12, and prenatal formulas generally skip vitamin A in the retinol form. Products advertising many times the Daily Value of a nutrient are a different category from a basic multivitamin. Source: NIH Office of Dietary Supplements fact sheet, linked below.
Who Should Be Cautious
Per the NIH fact sheet, a basic multivitamin with nutrients near recommended amounts should be safe for healthy people. The main risks come from stacking. Combining a multivitamin with other supplements and fortified foods can push some nutrients above their Tolerable Upper Intake Level.
Blood thinners: people taking warfarin or similar drugs should talk to their provider before taking any multivitamin containing vitamin K, which reduces warfarin's effectiveness.
Smokers and former smokers: avoid products with large amounts of beta-carotene or vitamin A. Two large trials linked high-dose beta-carotene to higher lung cancer risk in smokers.
Households with young children: the FDA requires iron-containing supplements to carry the warning that accidental iron overdose "is a leading cause of fatal poisoning in children under 6." Keep them out of reach.