More than 7 million Americans currently live with Alzheimer’s dementia, a number projected to climb to nearly 13 million by 2050, which has researchers looking hard for any accessible, modifiable factor that might shift that trajectory. A new study from Emory University’s Nell Hodgson Woodruff School of Nursing, published in Sleep Medicine, points to one: vitamin D supplementation, at a notably high dose, in adults who already show early warning signs of cognitive decline.
The study followed 54 adults who had both sleep disturbances and mild cognitive impairment (MCI), a condition researchers consider an early marker on the path toward dementia. Participants who reported taking at least 5,000 IU of vitamin D daily scored more than 13 percent higher on the Montreal Cognitive Assessment than those who didn’t, after the researchers accounted for other contributing factors. Lower daily doses weren’t associated with any cognitive benefit, and it made no difference whether participants took the D2 or D3 form of the vitamin.
The sleep connection isn’t incidental to the study’s design. Vitamin D affects muscle and nerve function as well as sleep quality, and the researchers cite Mayo Clinic data showing that roughly half of people with moderate to severe Alzheimer’s report sleep disturbances — a relationship the field increasingly suspects runs in both directions, with poor sleep and cognitive decline each potentially worsening the other. Vitamin D deficiency has separately been linked to sleep disorders in its own right.
Senior author Victoria Pak and colleagues describe the study as preliminary — the first, they say, to examine the relationship between vitamin D supplement intake and cognition specifically in this higher-risk group — and suggest this stage may represent a critical window for intervention, noting that identifying accessible, modifiable factors like vitamin D supplementation could matter most to patients before cognitive decline progresses further. The work was funded by the National Institute on Aging.
Journal: Sleep Medicine
Article Title: High-dose vitamin D may improve cognition among those at risk of dementia, Emory study finds
DOI: 10.1016/j.sleep.2026.108960
Publication Date: September 28, 2026
Source: EurekAlert