The study included 54 adults with sleep disturbances and mild cognitive impairments (MCI), both of which can be associated with the early stages of dementia. Participants who reported taking at least 5,000 IU of vitamin D each day performed better on measures of cognitive function than those who did not take vitamin D.

Higher Vitamin D Intake Linked to Better Cognitive Scores

The findings, recently published in Sleep Medicine, showed that people taking 5,000 IU or more of vitamin D daily scored more than 13% higher on the Montreal Cognitive Assessment (MoCA) compared with participants who took none, even after researchers adjusted for other factors.

MoCA is a widely used screening test designed to assess memory, thinking skills, and the risk of developing dementia. In contrast to the results seen with the higher intake group, lower daily doses of vitamin D were not associated with improved cognitive scores.

The researchers also highlighted the potential importance of when an intervention takes place. MCI is an intermediate stage between normal cognitive aging and dementia.

“In older adults experiencing both sleep disturbance and mild cognitive impairment, this may represent a critical window for intervention, when cognitive changes are emerging, but opportunities to support brain health may remain,” says Victoria Pak, senior author of the study.

“Identifying accessible and modifiable factors, such as vitamin D supplement intake, during the earlier stages of cognitive decline may become increasingly important, particularly as rates of Alzheimer’s disease continue to rise,” adds Pak, associate professor at Emory University’s Nell Hodgson Woodruff School of Nursing.

Vitamin D2 and D3 Showed Similar Results

The researchers also examined whether the form of vitamin D made a difference. Cognitive performance was similar among people taking vitamin D2, which is typically obtained from plants or fungi, and vitamin D3, which the body produces after sun exposure and which can also come from animal-based foods.

Vitamin D is an essential nutrient involved in muscle and nerve function, and it also plays a role in sleep quality and sleep-wake cycles. Sleep problems are common among people with Alzheimer’s disease. 50% of those with moderate to severe Alzheimer’s disease report sleep disturbances, pointing to a two-way relationship between poor sleep and cognitive decline.

Sleep Problems and Early Cognitive Decline

Vitamin D deficiency has previously been associated with sleep problems including insomnia and more frequent nighttime awakenings. This preliminary study is the first to examine how vitamin D supplement intake relates to cognitive function specifically in a high-risk group experiencing both MCI and sleep disturbances.

The study was funded by the National Institute on Aging of the National Institutes of Health, R01AG097853-01 and R61AG080606.

Other Emory co-authors also include Sirui Zhou, Paul Sudeshna, Lynn Marie Trotti, and Donald Bliwise.