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Researchers analyzed participants of the Rush Memory and Aging Project (MAP)—an ongoing longitudinal study that aims to identify risk factors for Alzheimer’s disease and other cognitive decline disorders—before and after death to see how their vitamin D levels affected cognitive function in their later years.

Free of known dementia at the time of enrollment, all MAP participants agreed to participate in annual evaluations and organ donation when they died. In this study, the average age of participants was 92 at the time of death.

Total serum vitamin D levels [25(OH)D] and global cognitive function were assessed antemortem, while vitamin D3, 25(OH)D3, and 1,25(OH)D3 (the active form of vitamin D3) were measured in four brain regions (the mid-temporal cortex, mid-frontal cortex, cerebellum, and anterior watershed white matter) post-mortem.

The main form of vitamin D3 found in the brain (and thus, the form researchers focused on in their analysis) was 25(OH)D3. It’s worth noting that there are two types of vitamin D—D2 and D3—and brain concentrations of vitamin D2 (the form found in most fortified food sources) were not measured in this study.

Vice president of scientific affairs at mindbodygreen Ashley Jordan Ferira, Ph.D., RDN, elaborates on this limitation: “Vitamin D3 is found in animal sources and key algae and lichen, while vitamin D2 comes from plant sources like yeast and irradiated mushrooms. If your health care provider accidentally measured serum 25(OH)D3, but you were knocking back irradiated mushrooms or a vitamin D2 supplement, your lab results wouldn’t reflect your intake. Serum total 25(OH)D is best to capture the full picture.”

While the results of this study are still pertinent to dementia research, it’s important to keep this discrepancy in mind as you read the results.

The study found that vitamin D3 in the brain does, indeed, support cognitive health: Higher post-mortem brain concentrations of 25(OH)D3 were associated with better cognitive function scores prior to death. Higher 25(OH)D3 concentrations in the anterior watershed white matter, specifically, was associated with better episodic memory and perceptual speed.

Participants with higher brain 25(OH)D3 concentrations also had 25% to 33% lower odds of having dementia or mild cognitive impairment (MCI) at their last visit before death. That said, no significant association between brain concentrations of 25(OH)D3 and dementia-related neuropathology was found.

Finally, the study found that plasma total 25(OH)D3 and free 25(OH)D levels were correlated with 25(OH)D3 concentrations in the four regions of the brain, suggesting our blood levels of vitamin D3 and free 25(OH)D may signify the amount of vitamin D3 in our brains as well. This is a valuable insight, considering brain concentrations of 25(OH)D3 cannot be measured while we are still alive.=

While it’s too early to determine vitamin D3’s exact role in cognitive health, researchers hypothesize that higher brain 25(OH)D3 concentrations may indicate cognitive resilience or be more relevant to semantic and working memory. Future research is needed to continue to explore the exact mechanisms of vitamin D in the brain.

That said, it’s never too early to get your vitamin D levels checked to ensure your body is getting enough of this essential vitamin. (Chances are, they’re low—29% of U.S. adults2 are vitamin D deficient, and a whopping 41% are insufficient!)

To maintain healthy D status and support the many facets of health that vitamin D impacts (including its demonstrated brain health benefits—e.g., mood support, attention, etc.—that have been thoroughly researched thus far), consider adding a high-quality vitamin D supplement to your daily routine (you can find mbg’s top picks here).

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