By Lara Moore

Credit: Unsplash/CC0 Public Domain

With more than 7 million Americans living with Alzheimer's dementia—a number projected to reach nearly 13 million by 2050—new Emory University research suggests that higher vitamin D supplement intake may be associated with better cognitive function in adults at elevated risk of dementia.

In a study of 54 adults with sleep disturbances and mild cognitive impairment (MCI), two hallmarks of early dementia, participants taking at least 5,000 IU of vitamin D daily showed better cognitive function than 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 the 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," said 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," added 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 consumption of 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 problems, 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.

More information: Sirui Zhou et al, Vitamin D supplement intake is associated with better cognition in persons with sleep disturbance and mild cognitive impairment, Sleep Medicine (2026). DOI: 10.1016/j.sleep.2026.108960