March 2, 2023 — Taking vitamin D may help prevent dementia, a large new study suggests.

Older people who took the supplement were 40% less likely to develop the disease over a 10-year period, compared to people who didn’t take any extra vitamin D.

“We know that vitamin D has some effects in the brain that could have implications for reducing dementia,” researcher Zahinoor Ismail, MD, of the University of Calgary and University of Exeter, says in a statement. “However so far, research has yielded conflicting results. … Overall, we found evidence to suggest that earlier supplementation might be particularly beneficial, before the onset of cognitive decline.”

The study, published this week in Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, compared the onset of dementia symptoms based on whether people took vitamin D supplements or not. The study enrolled a total of 12,388 people in the U.S. who did not have dementia when they signed up for the study. The average age of participants was 71. 

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Dementia Symptoms

Dementia describes the group of symptoms people have when they lose or injure brain cells.

Overall, 75% of people in the study who didn’t take vitamin D developed dementia within 10 years, and 25% of people who took vitamin D also developed dementia.

The researchers found that vitamin D gave greater protective benefits among women than men, although protection among both sexes was significant compared to not taking any vitamin D. Also, protection appeared to be better if people started taking the supplement before any signs of cognitive issues.

Vitamin D was significantly less protective against the onset of dementia in people who carry a specific gene that is associated with Alzheimer’s disease called the APOE4 gene. That’s possibly because the gene impacts how the body absorbs vitamin D, the study authors suggest. 

More than 50 million people worldwide have dementia, and that number will triple by 2050, the authors write.  Dementia refers to the reduced ability to remember, think, or make decisions in ways that impact everyday activities, according to the CDC. It mostly affects older people but is not considered a normal part of aging.