In a study of 54 adults with sleep disturbances and mild cognitive impairments (MCI), two hallmarks of early dementia, participants taking at least 5,000 IU of vitamin D daily showed better cognitive function compared to those who didn’t.

The study, recently published in Sleep Medicine, found that participants who reported taking 5,000 IU or more of vitamin D daily scored more than 13% higher on the Montreal Cognitive Assessment (MoCA) than those who didn’t, even after accounting for other factors. A screening tool to detect risk of developing dementia, MoCA is widely used to assess memory and thinking skills. In this study, lower daily doses of vitamin D were not associated with higher cognitive scores.

The study also emphasizes the significance of timing. 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.

In addition to the timing of the intervention, the study also found that cognitive performance did not differ based on the form of vitamin D — D2, typically derived from plants or fungi, or D3, produced after sun exposure or consuming animal-based foods.

Vitamin D, an essential nutrient, is not only necessary for muscle and nerve function, but also influences sleep quality and sleep-wake cycles. Additionally, 50% of those with moderate to severe Alzheimer’s disease report having sleep disturbances, indicating a bidirectional relationship between sleep deprivation and cognitive decline.

While vitamin D deficiencies have been implicated in sleep disorders, such as insomnia and more nighttime awakenings, this preliminary study is the first to assess the relationship between vitamin D supplement intake and cognitive function in a high-risk population with both MCI and sleep disturbances.

This 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.