Multivitamins have ballooned into a $40 billion industry in the United States. In a world captivated by quick fixes, there’s a seductive call in the idea that vitamin supplement might help to prevent age-related health decline. But does this promise hold up under scientific scrutiny?
JoAnn Manson, professor of medicine at Harvard Medical School and chief of preventive medicine at Brigham and Women’s Hospital, suggests that multivitamins may indeed play a role—particularly when combined with a healthy diet. Manson has been at the forefront of research into the potential of multivitamins to reduce risks associated with cancer and cognitive decline.
One of the most notable findings comes from the Physician’s Health Study (PHS) II, a randomized trial revealing an eight percent reduction in cancer risk among participants age 50 and older who took a daily multivitamin. Compared with a placebo, the study revealed a statistically significant decrease in total cancer incidence.
Similarly, multivitamins show promise in slowing age-related cognitive decline. A recent multivitamin clinical study led by Manson within the COcoa Supplement and Multivitamin Outcomes Study (COSMOS), involving more than 5,000 participants age 60 and older, found that daily multivitamin use could slow memory loss, effectively reducing cognitive aging by as much as two years. Although these findings appear encouraging, Manson emphasizes the need for further research to fully understand how multivitamins contribute to healthy aging, especially as part of broader dietary and lifestyle strategies.
Multivitamins for Older Adults—but Not as a Diet Replacement
Although multivitamins and plant-based diets have not been directly compared in clinical trials, Manson suggests they complement each other—especially for older adults, who may experience gaps in nutrition or difficulties absorbing and digesting nutrients. Multivitamins offer a safety net for micronutrient deficiencies, while plant-based diets deliver the fuel and fiber necessary for systemic health.
Manson recently co-authored a study published in the American Journal of Clinical Nutrition that found a significant reduction in cardiovascular and coronary heart disease risk when participants maintained a 1:2 ratio of plant-to-animal dietary protein. This supports the case for incorporating more plant-based foods into daily meals, as they provide fiber, improve gut health, and promote overall caloric balance.
As she explains, “The overall pattern of the diet matters more than any specific food.” A healthy diet delivers the right blend of fiber, proteins, fats, and carbohydrates. “You can’t take a really unhealthy diet that’s full of red meat and processed foods, throw a multivitamin at it, and expect good health,” Manson says. Fiber aids digestion, while proteins and fats help rebuild and protect muscles and the brain. Carbohydrates, on the other hand, provide the energy required to fuel bodily functions and physical activity.
Plant-based diets, rich in fruits, vegetables, whole grains, legumes, and plant-based proteins, can also support gut health, said Manson, improving digestion and enhancing the gut-brain connection—which is crucial for cognitive and overall health. Indeed, medical consensus now holds that microbes within the gut aid health in many ways (see “You Are What (Your Microbes) Eat,” November-December 2023). So, while a multivitamin alone may help deliver necessary nutrients, it can't stand in for the digestive benefits that come from a plant-based diet.
Multivitamins are an adjunct to overall diet: for older adults, however, they may be secret superheroes, according to Manson. Manson plans a new randomized trial of multivitamins to further explore supplements’ role in promoting healthy aging.
