Does a daily multivitamin improve health or longevity? Decoding the claim

A daily multivitamin is one of the most commonly taken supplements in the world, often bought less for a specific deficiency than for a general sense that it improves health and adds years. The evidence on that broad claim is larger and better studied than most supplement claims, and it does not support it in the way the marketing implies.

What the largest cohort study found

The most recent and largest study is Loftfield and colleagues (JAMA Network Open, 2024), which pooled three long-running prospective cohorts, the NIH-AARP Diet and Health Study, the PLCO Cancer Screening Trial cohort, and the Agricultural Health Study, for a combined 390,124 generally healthy US adults with up to 27 years of follow-up. Comparing daily multivitamin users with non-users, the study found no mortality benefit. If anything, the point estimate ran the opposite direction: in the first 12 years of follow-up, daily use was associated with a 4% higher rate of all-cause mortality (hazard ratio 1.04, 95% CI 1.02 to 1.07), a small but statistically significant finding, and a similar, no-longer-significant hazard ratio of 1.04 (95% CI 0.99 to 1.08) in the following 15 years. Cause-specific results for heart disease and cerebrovascular mortality were similarly flat or slightly unfavorable, while cancer mortality was essentially unchanged.

This is an important result, but it needs to be read as what it is: a large observational cohort study, not a randomized trial. The authors themselves flagged the two competing biases that plague this kind of research, a “healthy user effect,” where people who take supplements also tend to have generally healthier habits that could mask a real benefit, and a “sick user effect,” where a new or worsening health condition prompts someone to start supplementing, which could manufacture a false-positive association with worse outcomes. The study’s design tried to account for both, but neither can be fully ruled out in cohort data the way it can in a randomized trial. The honest reading is that this large study found no evidence of a longevity benefit from daily multivitamin use, not that multivitamins have been proven to shorten life.

What the randomized trial evidence found

The strongest randomized evidence on this question comes from the Physicians’ Health Study II, which randomly assigned 14,641 male US physicians aged 50 and older to a daily multivitamin or placebo and followed them for a median of 11.2 years, the closest thing this field has to a definitive controlled trial. On cancer, Gaziano and colleagues (JAMA, 2012) found a modest but statistically significant 8% reduction in total cancer incidence in the multivitamin group, with no significant effect on cancer mortality and no effect on prostate cancer specifically, the most common cancer in the cohort. On cardiovascular disease, a companion trial report from the same cohort, Sesso and colleagues (JAMA, 2012), found no significant reduction in major cardiovascular events, including heart attack, stroke, or cardiovascular death, from the same daily multivitamin regimen.

Taken together, the one large randomized trial built to test this question directly found a small, real benefit for one outcome (total cancer incidence) and no benefit for the outcome most people associate with general health protection (cardiovascular disease). That is a genuinely mixed randomized result, not a clean positive or a clean null, and it was conducted only in older men, which limits how far it generalizes.

Where the USPSTF and a cognition trial complicate the picture

The US Preventive Services Task Force reviewed this same body of evidence in 2022 and issued an “I” statement, meaning the evidence is insufficient to weigh the benefits and harms of multivitamin supplementation for preventing cardiovascular disease or cancer in community-dwelling, non-pregnant adults without a diagnosed deficiency. That is a formal acknowledgment that the trial and cohort evidence, taken as a whole, does not clear the bar for a positive population-wide recommendation, while stopping short of recommending against use.

One further randomized trial complicates a purely negative summary. COSMOS-Mind (Baker and colleagues, Alzheimer’s & Dementia, 2023), a substudy of the larger COSMOS trial, randomized older adults to a daily multivitamin-mineral or placebo and found a statistically significant benefit on global cognition over three years (mean z-score difference 0.07, 95% CI 0.02 to 0.12, P = .007), with a larger effect in participants who had a history of cardiovascular disease. This is a real, randomized, positive signal, but it is narrow: it speaks to cognitive test performance in older adults, not to the broader “improves health and longevity” claim, and it has not yet been matched by a similarly sized trial confirming a downstream benefit like reduced dementia diagnoses.

Where a documented deficiency changes the picture

All of the trials and cohorts above studied generally healthy adults without a known nutrient deficiency, taking a multivitamin as a broad preventive measure. That is a different situation from someone with a documented micronutrient gap, whether from a restrictive diet, a malabsorptive condition, older age with reduced dietary variety and intake, or a specific lab-confirmed deficiency. Correcting an actual, identified nutritional shortfall is a narrower and more defensible use of a multivitamin or targeted single-nutrient supplement than taking one as a general hedge against disease, and whether a given diet or health situation constitutes that kind of gap is a determination for a clinician or registered dietitian working from an individual’s actual intake and lab values, not something a population-level trial can answer in the abstract.

The honest bottom line

The evidence for a daily multivitamin improving general health or extending life in already well-nourished adults is weak. The largest cohort study to date found no mortality benefit, and its point estimate leaned slightly the other way. The best available randomized trial found a small, real reduction in total cancer incidence but no cardiovascular benefit, and the USPSTF has formally concluded the evidence is insufficient to recommend multivitamins for preventing cardiovascular disease or cancer. A single trial’s cognition signal in older adults is a genuine, randomized positive finding, but a narrow one, and it does not add up to broad support for the longevity claim as it is typically marketed.