Daily Multivitamin May Slow Biological Aging, Trial Finds

A Pill a Day Keeps the Epigenetic Clock at Bay?

For decades, the case for daily multivitamins has been murky — helpful for some, unnecessary for others. A major new clinical trial has now added a striking finding to that debate: a daily multivitamin may measurably slow the biological aging process, at least as captured by cutting-edge epigenetic tools. The results, published in Nature Medicine in March 2026, are among the most rigorous evidence yet that common supplements can influence the cellular machinery of aging.

What the COSMOS Trial Found

The research is an ancillary analysis of the COcoa Supplement and Multivitamin Outcomes Study (COSMOS), a large randomized controlled trial run by investigators at Mass General Brigham. Of the trial's broader cohort, 958 participants — with an average chronological age of 70 — were selected for epigenetic analysis. Over two years, those assigned to a daily multivitamin (Centrum Silver) showed a statistically significant slowing of biological aging compared to those on a placebo.

The effect, measured using DNA methylation-based epigenetic clocks, translated to roughly 2.7 to 5.1 fewer months of biological aging over the trial period. Two second-generation clocks — PCGrimAge and PCPhenoAge — detected the benefit; three others, including the well-known Horvath clock and DunedinPACE, showed no significant difference. Importantly, cocoa extract supplementation produced no measurable effect on any of the clocks.

The benefit was not uniform across participants. Those who began the trial with accelerated biological aging — meaning their biological age outpaced their chronological age — saw roughly double the slowing effect on PCGrimAge, suggesting that nutritional deficiencies may be a key driver of the mechanism.

Why It Matters

Epigenetic clocks work by tracking DNA methylation — chemical tags on the genome that accumulate and shift with age. These clocks have become leading tools in aging research because they correlate with mortality risk, disease onset, and overall health trajectory. The COSMOS ancillary study is described by its authors as the first large-scale randomized controlled trial to examine the effects of a standard dietary supplement on these clocks.

"The public appetite for knowing whether everyday supplements can genuinely slow ageing is enormous," said Steve Horvath, a geroscientist at Altos Labs, who called the study "very interesting and rigorous." The Harvard Gazette highlighted the trial's scale and design as lending it unusual credibility in a field often plagued by small, poorly controlled studies.

Reasons for Caution

Experts are careful not to overstate the findings. Epigenetic clocks are powerful research instruments but are rarely used as clinical diagnostics, and improving a clock reading does not automatically translate to better health outcomes.

"There's a critical piece of evidence that's missing: whether people who take multivitamins have a corresponding improvement in their actual healthspan," one researcher told Chemical & Engineering News.

The COSMOS findings are correlational within a randomized framework — they show an association between supplementation and slower epigenetic aging, but cannot yet confirm that this change reduces disease risk or extends healthy life. Researchers also note that the 958-person subsample, while substantial, is far smaller than the full COSMOS cohort of over 21,000 participants.

The Bottom Line

The COSMOS trial does not settle the multivitamin debate, but it meaningfully advances it. For older adults — particularly those with nutritional gaps — a daily multivitamin may do more than plug dietary deficiencies. It may, at least in biological terms, buy a few extra months of youth. Whether those months translate into longer, healthier lives remains the key question for future research.