A daily multivitamin slowed biological aging by four months over two years in a randomized trial

Nature Medicine, March 2026. DOI: 10.1038/s41591-026-04239-3

Your cells may be aging faster or slower than the calendar suggests. This gap between chronological age and biological age, measured by chemical markers on DNA, has become one of the most closely watched metrics in aging research. And a new analysis from a large randomized trial suggests that something as simple as a daily multivitamin might widen that gap in a favorable direction.

The study, published in Nature Medicine, used data from the COcoa Supplement and Multivitamin Outcomes Study (COSMOS) to evaluate whether daily multivitamin use affects five established measures of biological aging. Over two years, participants taking a multivitamin showed slower aging across all five epigenetic clocks, with the effect equivalent to roughly four months of reduced biological aging.

Epigenetic clocks and what they measure

Epigenetic clocks estimate biological age by analyzing patterns of DNA methylation, small chemical modifications that accumulate at specific sites along the genome as people age. Different clocks weight different sites and are calibrated against different outcomes. Some predict chronological age; others are tuned to predict mortality or the pace of biological decline.

The COSMOS analysis examined five such clocks using blood samples from 958 randomly selected participants with an average chronological age of 70. Participants had been randomized into four groups: daily cocoa extract plus multivitamin, cocoa extract plus placebo, placebo plus multivitamin, or placebos only. Blood samples were analyzed at the start of the trial and at the end of years one and two.

Compared with the placebo-only group, participants taking a multivitamin showed slowing across all five clocks. The effect reached statistical significance for the two clocks most strongly predictive of mortality. The cocoa extract, by contrast, did not produce a consistent signal.

Who benefited most

The most intriguing finding may be that participants who entered the trial with accelerated biological aging, meaning their epigenetic clocks read older than their actual years, showed the greatest benefit from multivitamin use. This suggests the intervention may be most valuable for people whose biology is already outpacing the calendar, though the mechanism behind this differential effect remains unclear.

Senior author Howard Sesso, associate director of the Division of Preventive Medicine at Mass General Brigham, framed the finding in terms of accessibility. A daily multivitamin is inexpensive, widely available, and generally safe. If the biological aging effects are real and durable, the public health implications could be significant simply because the intervention is so easy to adopt.

What this does not prove

Several important caveats apply. First, four months of slowed biological aging over two years is a modest effect. Whether this translates into meaningful clinical benefits, such as reduced disease risk or longer lifespan, has not been demonstrated. Epigenetic clocks are biomarkers, not health outcomes. A slower clock does not necessarily mean a healthier or longer life.

Second, the study population consisted of generally healthy older adults. The results may not generalize to younger people, to those with significant health conditions, or to populations with different nutritional baselines. People who are already nutritionally replete may not benefit from supplementation in the same way as those with deficiencies.

Third, the study does not reveal which specific nutrients in the multivitamin are driving the effect, or through what biological mechanisms they might influence DNA methylation patterns. A multivitamin contains dozens of compounds, and isolating the active ingredients will require further research.

The COSMOS team plans follow-up studies to determine whether the slowing of biological aging persists after the trial ends, and whether it correlates with improvements in clinical outcomes the trial has already shown evidence for, including cognition and cancer incidence.

Disclosure context

The trial received infrastructure support and study pill donations from Mars Edge (a segment of Mars Incorporated) and Pfizer Consumer Healthcare (now Haleon), which manufactured the Centrum Silver multivitamins used in the study. Neither company had a role in trial design, data analysis, or manuscript preparation. Several investigators reported additional industry relationships, detailed in the published disclosure statements.