Although over-the-counter multivitamins are generally considered safe, many health experts view them as unnecessary unless a person has a diagnosed vitamin deficiency. Despite this skepticism, supplements remain popular: about one in three Americans takes a vitamin supplement, and once-daily multivitamins account for roughly 40 percent of all vitamin sales in the U.S.

Recent research suggests there may be a meaningful benefit worth reconsidering—particularly for cognitive health in older adults.

Dementia is a progressive loss of cognitive function that interferes with daily life, affecting memory, reasoning, and thinking. As life expectancy increases, the global burden of dementia is expected to rise sharply. Risk factors such as obesity, smoking, and high blood sugar further contribute to this trend.

A 2022 projection published in The Lancet estimated that the number of Americans living with dementia will double by 2050, increasing from approximately 5.2 million to 10.5 million. These projections highlight the urgent need for safe, accessible interventions that may help slow cognitive decline.

Multivitamins and Cognitive Function: Surprising Findings

A large clinical trial conducted as part of the COSMOS (Cocoa Supplement and Multivitamin Outcomes Study), in collaboration with Brigham and Women’s Hospital, evaluated whether cocoa extract or a daily multivitamin could reduce the risk of cardiovascular disease, cancer, stroke, and cognitive decline.

The study included 21,442 adults aged 65 and older (average age 73), with participants randomized to receive either cocoa extract, a multivitamin-mineral supplement, both, or placebo. Cognitive testing was conducted by phone at baseline and annually for three years, assessing memory, verbal fluency, processing speed, and accuracy.

Researchers initially expected cocoa extract—rich in flavanols known to support cardiovascular health and cerebral blood flow—to provide the greatest cognitive benefit. However, cocoa supplementation showed no measurable cognitive improvement compared to placebo.

Unexpectedly, participants taking a daily multivitamin demonstrated statistically significant cognitive benefits. Investigators estimated that three years of multivitamin use slowed cognitive decline by approximately 60 percent, equivalent to about 1.8 years of preserved cognitive aging.

Why Micronutrients May Matter for Brain Health

This study represents the first large, long-term clinical trial to demonstrate a cognitive benefit from multivitamin supplementation in older adults. Several vitamins and minerals are essential for normal brain function, and even mild deficiencies—more common with aging—may increase the risk of cognitive decline and dementia.

Notably, the cognitive benefits were more pronounced in participants with existing cardiovascular disease, a population already at higher risk for cognitive impairment. This finding supports the link between cardiovascular health and brain health.

Nutrition Still Comes First

While multivitamins may offer some protection against cognitive decline, they are not a substitute for good nutrition. Even modest vitamin and micronutrient deficiencies can negatively affect brain function, emphasizing the importance of a nutrient-dense diet.

General dietary strategies associated with brain health include:

• Following a Mediterranean-style (or "Keto" style) diet rich in fruits, vegetables, legumes, nuts, seeds, olive oil, fish, and limited red or processed meats

• Including omega-3–rich foods such as fatty fish, walnuts, flaxseeds, and soybeans

• Limiting excess sugar and red meat intake

• Ensuring adequate daily fruit and vegetable consumption, which many adults currently fall short of recommended levels.

Bottom Line

While multivitamins have long been considered optional for many adults, emerging evidence suggests they may play a role in slowing cognitive decline in older populations—particularly those with cardiovascular risk factors.