Benefits
What the 11-year PHS II trial in male physicians did and did not find
In 14,641 male US physicians aged 50 and over, followed a median 11.2 years, a daily Centrum Silver reduced total cancer diagnoses from 18.3 to 17.0 per 1,000 person-years (HR 0.92, 95% CI 0.86 to 0.998, p=0.04). That is the whole of the positive result. There was no effect on prostate cancer (HR 0.98), colorectal cancer (HR 0.89), lung cancer (HR 0.84), cancer mortality (HR 0.88, p=0.07) or death from any cause (HR 0.94, p=0.13). The larger figure often quoted for the 1,312 men with a previous cancer (HR 0.73) is a subgroup, and it did not differ significantly from the rest of the trial (p for interaction 0.07). One trial, in one unusually healthy and well-nourished group of doctors, is not a reason to take a multivitamin in the hope of avoiding cancer.
COSMOS: the trial that missed its main cancer endpoint
COSMOS randomized 21,442 US adults (women 65 and over, men 60 and over) to a daily Centrum Silver or placebo for a median 3.6 years. Its primary outcome, total invasive cancer, was null: 518 cases on multivitamin against 535 on placebo (HR 0.97, 95% CI 0.86 to 1.09, p=0.57). So were breast cancer (HR 1.06), colorectal cancer (HR 1.30), the cardiovascular composite (HR 0.98) and death from any cause (HR 0.93). One secondary site came out lower, lung cancer (HR 0.62, 95% CI 0.42 to 0.92), and that is a single positive finding among many comparisons inside a trial that missed the endpoint it was designed around. It has not been reproduced in an independent trial. The authors' own conclusion was that a daily multivitamin did not significantly reduce total cancer, and that 3.6 years may have been too short.
Cognitive aging slowed by about 2 years (COSMOS-Mind)
In 2,262 adults aged 65 and over, three years of a daily multivitamin improved a global cognition composite by 0.07 standard deviations against placebo (95% CI 0.02 to 0.12, p=0.007), with gains also in episodic memory and executive function. A 2024 pooled analysis of three non-overlapping cognitive substudies inside the same parent trial found the same 0.07 SD difference (95% CI 0.03 to 0.11, p=0.0009), which the authors describe as equivalent to about two years less cognitive aging. Two things a reader should know: the multivitamin comparison was the pre-specified secondary question in a trial whose primary agent, cocoa extract, did nothing (0.03 SD, 95% CI -0.02 to 0.08, p=0.28), and every result here comes from one parent trial, so no independent group has reproduced it. The reported advantage in people with a cardiovascular history did not reach significance on its own (0.14, 95% CI -0.02 to 0.31).
Filling micronutrient gaps in suboptimal diets
Counting food, fortified food and supplements together, NHANES 2003 to 2006 (n=16,110, ages 2 and over) put the share of Americans below the Estimated Average Requirement at 70 percent for vitamin D, 60 percent for vitamin E, 45 percent for magnesium, 38 percent for calcium, 34 percent for vitamin A and 25 percent for vitamin C. Potassium and vitamin K are set as Adequate Intakes rather than EARs, and only 3 percent and 35 percent of the population respectively reached them. In a separate NHANES analysis (2009 to 2012, n=10,698), adults taking a multivitamin at any frequency had a lower prevalence of inadequate intake for 15 of 17 nutrients examined, while intakes above the Tolerable Upper Intake Level rose for 7 nutrients, affecting no more than 4 percent of users for any one of them. Calcium, magnesium and vitamin D shortfalls persisted even in the most frequent users. Closing a measured shortfall is the clearest and best documented thing a daily multivitamin does, and it matters most for older adults, restrictive dieters and people with impaired absorption.
Mechanism of action
Replenishing micronutrient cofactors for hundreds of enzymatic reactions
B vitamins serve as cofactors for energy metabolism (B1, B2, B3, B5), one-carbon metabolism (B6, B9, B12), and DNA synthesis. Magnesium, zinc, and selenium serve as cofactors for hundreds of enzymes including those involved in DNA repair, antioxidant defense (superoxide dismutase, glutathione peroxidase), and immune function. Even subclinical deficiencies impair enzymatic function and may accelerate aging-related decline.
Antioxidant defense (vitamins C, E, selenium, zinc)
Vitamins C and E and the trace minerals selenium, zinc, and copper support cellular antioxidant defense. Selenium-dependent glutathione peroxidase, copper/zinc-dependent superoxide dismutase, and vitamin C/E recycling all require adequate micronutrient status. This is a plausible mechanism and nothing more. In the two large trials that measured cancer directly, one found a small difference in total diagnoses and the other found none at all, so nothing in this pathway has been shown to produce a clinical result.
Micronutrient roles in immune cells and DNA methylation
Multiple micronutrients (vitamins A, D, E, B6, B12, folate, zinc, selenium, iron, copper) are essential for innate and adaptive immune function. Folate and B12 support DNA methylation patterns and chromosome stability. These are textbook biochemical roles, worked out from deficiency states. They are not evidence that a multivitamin improves immune function in someone already replete. In 910 community-dwelling adults aged 65 and over, a year of a daily multivitamin and multimineral did not reduce self-reported days of infection or contacts with primary care for infection. A separate 12-week randomized placebo-controlled trial in 42 healthy adults aged 55 to 75 measured whole-blood bacterial killing, neutrophil phagocytosis, salivary IgA and plasma cytokines and found no change in any of them, though a trial that small could not detect a modest effect.
Clinical trials
Large-scale randomized, double-blind, placebo-controlled trial (Gaziano JM, Sesso HD, Christen WG, Bubes V, Smith JP, MacFadyen J, Schvartz M, Manson JE, Glynn RJ, Buring JE 2012, JAMA 308(18):1871-1880, doi:10.1001/jama.2012.14641).
14,641 male U.S. physicians initially aged ≥50 (mean age 64.3). Including 1,312 men with cancer history. Randomized to daily Centrum Silver multivitamin or placebo. Treatment and follow-up 1997-2011 (median 11.2 years).
Total cancer incidence significantly reduced: 17.0 vs 18.3 events per 1,000 person-years (HR 0.92, 95% CI 0.86-0.998, p=0.04), an 8% relative reduction. No significant effect on prostate cancer (HR 0.98), colorectal cancer (HR 0.89), or lung cancer (HR 0.84). Effect stronger in men with cancer history (HR 0.73) and men ≥70 (HR 0.82). 2,757 men (18.8%) died during follow-up, including 859 (5.9%) from cancer; neither cancer mortality (403 vs 456 deaths; HR 0.88, 95% CI 0.77-1.01, p=0.07) nor death from any cause (1,345 vs 1,412 deaths; HR 0.94, 95% CI 0.88-1.02, p=0.13) differed significantly between groups. Both subgroup results above are exploratory: the difference between men with and without a prior cancer was not statistically significant (p for interaction 0.07), and neither was the difference across age groups (p for interaction 0.06). Funding came from National Institutes of Health grants and an investigator-initiated grant from BASF Corporation, and the Centrum Silver was supplied by Pfizer, which made it.
Randomized, double-blind, placebo-controlled trial (Sesso HD, Rist PM, Aragaki AK, Rautiainen S, Johnson LG, Friedenberg G, Copeland T, Clar A, Mora S, Moorthy MV, Sarkissian A, Wactawski-Wende J, Tinker LF, Carrick WR, Anderson GL, Manson JE; COSMOS Research Group. 2022, Am J Clin Nutr 115(6):1501-1510, doi:10.1093/ajcn/nqac056, PMID 35294969). Published title: Multivitamins in the prevention of cancer and cardiovascular disease: the COcoa Supplement and Multivitamin Outcomes Study (COSMOS) randomized clinical trial.
21,442 U.S. adults (men ≥60 years, women ≥65 years). Randomized to daily Centrum Silver or placebo. Median follow-up 3.6 years.
Primary outcome (total invasive cancer) was NULL: 518 cases on multivitamin vs 535 on placebo, HR 0.97 (95% CI 0.86-1.09, p=0.57). Secondary: Lung cancer significantly reduced (HR 0.62, 95% CI 0.42-0.92). No significant effect on breast (HR 1.06), colorectal (HR 1.30), CVD composite (HR 0.98), or all-cause mortality (HR 0.93). Authors concluded 3.6 years may be too short to detect total cancer effect; longer follow-up needed, and their stated conclusion was that a daily multivitamin did not significantly reduce total cancer. The lung cancer result is one positive finding among many secondary comparisons in a trial that missed its primary endpoint, and no independent trial has reproduced it. COSMOS was funded by Mars Edge with additional National Institutes of Health grants, and the Centrum Silver was supplied by Pfizer Consumer Healthcare (now GSK Consumer Healthcare).
Ancillary study to COSMOS evaluating cognitive function (Baker LD, Manson JE, Rapp SR, Sesso HD, Gaussoin SA, Shumaker SA, Espeland MA 2023, Alzheimers Dement 19(4):1308-1319, doi:10.1002/alz.12767).
2,262 COSMOS participants ≥65 years (subset of larger trial). 3-year follow-up with annual cognitive assessments via telephone interview using composite of 5 tests covering global cognition, episodic memory, and executive function.
Daily multivitamin produced statistically significant improvement in global cognition vs placebo (effect size 0.07 SD, p=0.007), which the 2024 pooled analysis of the three COSMOS cognitive substudies describes as equivalent to about two years less cognitive aging. Significant improvements also in episodic memory and executive function. The apparent advantage in participants with a cardiovascular disease history did not reach significance on its own (0.14, 95% CI -0.02 to 0.31; interaction nominal p=0.01). The trial's primary agent, cocoa extract, had no effect on cognition (0.03, 95% CI -0.02 to 0.08, p=0.28). This is the largest randomized evidence available for a multivitamin and cognition, and it has not been reproduced outside the COSMOS trial.