A daily multivitamin taken for two years slowed certain DNA methylation measures of biological ageing in a randomized clinical trial, creating a narrow but meaningful inflection point in the conversation about supplements and ageing. The finding appears in a Nature Medicine paper that analyzed data from the COcoa Supplement and Multivitamin Outcomes Study (COSMOS).
What Is the Inflection Point?
The COSMOS ancillary analysis evaluated 958 participants (482 women and 476 men) over two years, testing daily multivitamin–multimineral (MVM) supplementation and a cocoa flavanol extract against placebos. Blood samples taken at baseline, one year and two years were assessed using five DNA methylation-based measures of biological ageing: PCHannum, PCHorvath, PCPhenoAge, PCGrimAge and DunedinPACE. Compared with placebo, daily MVM supplementation produced modestly smaller year-to-year increases for two second-generation epigenetic clocks: a between-group difference in yearly change of −0. 113 years for PCGrimAge and −0. 214 years for PCPhenoAge. The cocoa extract (500 mg cocoa flavanols per day, including 80 mg (−)-epicatechin) did not affect any of the five epigenetic clocks tested.
What Happens When multivitamin shifts epigenetic clocks?
The trial’s measurable but small slowing corresponds to roughly four months less biological ageing over two years on the mortality-linked clocks. The effect on PCGrimAge was larger among participants who began the trial with accelerated biological ageing than among those with normal or decelerated ageing. The study authors note nutritional status may partly explain the pattern, and they emphasize that whether these epigenetic shifts translate to concrete clinical benefits remains unresolved.
- Trial size and design: 958 participants randomized into four groups (multivitamin, cocoa extract, both, or double placebo) with sampling at baseline, one year and two years.
- Epigenetic outcomes: reductions seen for PCGrimAge (−0. 113 years/year) and PCPhenoAge (−0. 214 years/year); no effect for PCHannum, PCHorvath or DunedinPACE.
- Cocoa extract: 500 mg cocoa flavanols daily (including 80 mg (−)-epicatechin) showed no effect on the five clocks.
- Heterogeneity: stronger PCGrimAge effect in participants with accelerated biological ageing at baseline.
Dr Howard Sesso, an epidemiologist at Mass General Brigham department of medicine and senior author of the work, said the findings do not imply that all older adults must take multivitamins and that the clinical relevance needs further evaluation. The paper calls for additional studies to determine whether the observed epigenetic changes help explain prior findings linking multivitamin use to certain age-related outcomes.
What If This Scales? Three scenarios and what to do
Best case: Follow-up research confirms that the modest epigenetic slowing on mortality-linked clocks translates into measurable reductions in age-related disease incidence or severity. In this scenario, targeted multivitamin strategies for people with demonstrable nutritional deficits or accelerated biological ageing could become a low-risk public health tool.
Most likely: Additional trials reproduce small, heterogeneous epigenetic effects without clear, immediate clinical impact. Here, the result is an incremental refinement of how ageing biology is studied—informing who might benefit from supplementation but stopping short of broad clinical recommendations.
Most challenging: Larger or longer studies fail to link clock changes with meaningful health outcomes, or earlier contradictory evidence about longevity and safety remains unresolved. That outcome would maintain uncertainty and limit guideline changes.
Given these scenarios, practical next steps are clear and narrow: prioritize confirmatory trials that examine clinical endpoints alongside epigenetic measures; stratify participants by baseline nutritional status and biological-age markers; and preserve transparent data access for independent analysis, as the COSMOS research committee has outlined for controlled data requests. Uncertainty is explicit in the trial’s own conclusions: the statistical signals are small and their clinical import is unknown.
Readers should understand that the COSMOS randomized clinical trial produced modest, measurable slowing on two DNA methylation ageing clocks, that effects were concentrated in those with faster baseline ageing, and that cocoa flavanol supplementation showed no clock benefit. Policymakers, clinicians and consumers should watch for further trials that link epigenetic shifts to health outcomes before changing practice—especially when considering a daily multivitamin
