For decades, the effectiveness of multivitamins has been hotly debated in both the medical community and among the public. Many older adults dutifully swallow a daily pill, wondering if it makes any real difference. Now, a new study published March 9, 2026 in Nature Medicine is providing some of the most credible evidence yet that a daily multivitamin might actually slow down the aging process—at least at the cellular level.
Researchers from Harvard and Mass General Brigham, as well as Brigham and Women’s Hospital, analyzed the effects of taking a daily multivitamin over two years on five different measures of biological aging in a large, randomized clinical trial. This study, known as the COcoa Supplement Multivitamins Outcomes Study (COSMOS), involved 958 healthy participants—men over 60 and women over 65—with an average chronological age of 70. Participants were randomly assigned to one of four groups: a daily cocoa extract and multivitamin, a multivitamin only, a cocoa extract only, or placebos.
The researchers used blood samples taken at the start of the study, after 12 months, and again after 24 months to analyze changes in what are known as epigenetic clocks. These clocks estimate biological age by tracking DNA methylation, a process where small chemical tags are added to DNA and influence how genes are expressed as we age. Five such clocks were used in the study—including the well-known GrimAge and PhenoAge clocks—allowing scientists to track the pace of aging at a molecular level.
The results? Compared to the placebo group, those who took a daily multivitamin experienced a slowing of biological aging equivalent to about four months over the course of two years. Specifically, two of the five epigenetic clocks—both predictive of mortality—showed statistically significant slowing. In essence, during the 24 months of the trial, participants in the multivitamin group aged only about 20 months at the cellular level. The effect was even more pronounced for individuals whose biological age exceeded their chronological age at the start of the study, with some seeing double the benefit on certain measures, such as the PCGrimAge clock.
“There is a lot of interest today in identifying ways to not just live longer, but to live better,” said senior author Howard Sesso, an epidemiologist at Brigham and Women’s Hospital and Harvard Medical School, according to Nature Medicine. “It was exciting to see the benefits of a multivitamin linked with markers of biological aging. This study opens the door to learning more about accessible, safe interventions that contribute to healthier, higher-quality aging.”
However, Sesso was quick to temper expectations. “This doesn’t mean that everyone should go out and start taking a multivitamin,” he told Business Insider. “Rather, this is starting to provide the connecting dots.” He emphasized that while the results are promising, the effect is modest and it’s too early to recommend multivitamins for everyone based solely on these findings.
Other experts agree that the study’s findings are intriguing but should be interpreted with caution. Steve Horvath, a geroscientist at Altos Labs in Cambridge, UK, who developed one of the epigenetic clocks used in the study, told Nature, “This is a very interesting and rigorous study. The public appetite for knowing whether everyday supplements can genuinely slow aging is enormous. This study provides some of the most credible evidence we have to date.”
The study’s rigor sets it apart from many previous supplement trials. The research team measured aging using five different epigenetic clocks, which provide a more comprehensive view of biological aging than traditional health metrics like blood pressure or cholesterol. According to Daniel Belsky, an aging researcher at Columbia University who was not involved in the study, “Lots of things could cause variation in the epigenetic clocks that are not the biology of aging.” He pointed out that changes in these clocks have been observed in people undergoing surgery or during pregnancy—situations that may not reflect long-term health or longevity.
Importantly, the study does not claim that taking a multivitamin will add four months to your life. “What it means is that your trajectory of health moving forward should stand to benefit,” Sesso explained to NBC News. “It’s hard to know what those four months truly translate to.”
The study also highlighted that the benefits of multivitamins were greatest among those who were biologically older than their actual age at the start of the trial. This suggests that multivitamins might be particularly helpful for older adults who are already experiencing accelerated aging, possibly due to nutrient deficiencies or poorer health. As Sesso told Business Insider, there could be something about the “interconnectivity” of the different vitamins and minerals in a daily multivitamin “that might be working together in ways that we just don’t fully appreciate.”
Still, the study has its limitations. Most participants were healthy and white, so it’s unclear whether the findings would apply to a more diverse population or to those with chronic health conditions. The study was also funded in part by Haleon (formerly Pfizer Consumer Healthcare) and Mars Inc., which provided the multivitamins and cocoa extract, but neither company contributed to the study design or analysis. Additional funding came from the National Institutes of Health.
Experts caution that while the biomarkers used in the study are cutting-edge, more research is needed before scientists can definitively recommend daily multivitamin use as an anti-aging intervention. “We do not know yet whether [multivitamins] have an effect in improving tissue function or reducing disease risk,” Danica Chen, a professor at the University of California, Berkeley, told NBC News. The field of aging research “is at the stage that we are really just looking for even proof of concept.”
For now, most health professionals continue to recommend getting nutrients from a balanced, varied diet rather than relying on supplements. As Sesso himself noted, “I am a firm believer in diet, lifestyle and just healthy living, as best I can.” Joanne Slavin, a professor at the University of Minnesota, pointed out that older adults may have unique nutritional challenges—such as difficulty preparing meals or absorbing certain nutrients like vitamin B12—and could benefit from a multivitamin in some cases. However, she added, “There aren’t that many nutrients where we’d say, ‘Hey, older people need twice as much.’”
Looking ahead, researchers hope that as our understanding of biological aging improves, doctors might one day be able to tailor supplement regimens to an individual’s biological age, potentially optimizing health as we grow older. As Belsky told Business Insider, “Answers are coming, they’re coming soon. They’re just not here yet.”
While the promise of a daily pill that slows aging is enticing, experts agree that healthy aging remains a complex, multifaceted process. For now, the best advice is to focus on a balanced diet, regular physical activity, and social connections—supplemented, perhaps, by a daily multivitamin if recommended by your healthcare provider.