Adults struggling with both sleep disturbances and mild cognitive impairment (MCI) may find a path to improved brain function through high-dose vitamin D supplementation. A study of 54 participants, published in the October 2026 issue of the journal Sleep Medicine, offers a promising signal: those consuming 5,000 international units (IU) or more of vitamin D daily scored over 13% higher on the Montreal Cognitive Assessment (MoCA) than peers taking no supplements.
Dosage Thresholds and Brain Function
The research suggests that the benefits of vitamin D are dose-dependent. According to senior author Dr. Victoria Pak of the Emory University Nell Hodgson Woodruff School of Nursing, the findings suggest that lower daily doses of vitamin D do not yield the same cognitive benefits.
Crucially, the form of the supplement did not alter the results. Researchers noted that positive outcomes remained consistent regardless of whether participants took vitamin D2—often derived from plants or fungi—or vitamin D3, which is typically found in animal-based foods or produced via sun exposure. The study utilized the MoCA, a standard screening tool used to evaluate memory and executive thinking skills.
Targeting the Sleep-Cognition Cycle
Dr. Pak and her colleagues—Sirui Zhou, Paul Sudeshna, Lynn Marie Trotti, and Donald Bliwise—examined this intersection to address the bidirectional relationship between sleep deprivation and cognitive health.
Vitamin D is a nutrient essential for nerve and muscle function, and it also plays a role in regulating the sleep-wake cycle. While previous research has linked vitamin D deficiencies to insomnia and fragmented sleep, this study is the first to evaluate the link between supplement intake and cognitive scores in a population specifically diagnosed with both MCI and sleep problems.
A Critical Window for Intervention
The researchers identified the period of mild cognitive impairment as a potential “critical window” for intervention. As individuals transition between normal cognitive aging and the onset of dementia, support for brain health may still be effective.
Dr. Pak emphasized that finding accessible, modifiable factors like vitamin D intake is increasingly important as the number of Americans living with Alzheimer’s dementia is projected to climb from over 7 million to nearly 13 million by 2050. The research was supported by the National Institute on Aging of the National Institutes of Health.
Study Findings at a Glance
Does the form of vitamin D matter?
No. Researchers found that cognitive performance did not differ between participants taking vitamin D2 or vitamin D3.
How much vitamin D was associated with higher scores?
The study observed improved cognitive performance in individuals taking 5,000 IU or more per day. Lower doses were not linked to the same cognitive improvements in this participant group.
Why focus on people with sleep disturbances?
Sleep issues are common in those with MCI and moderate to severe Alzheimer’s disease. Because sleep and cognitive function share a bidirectional relationship, researchers sought to determine if vitamin D could serve as a modifiable factor for this specific high-risk population.
What is the Montreal Cognitive Assessment (MoCA)?
The MoCA is a widely used clinical screening tool designed to detect early cognitive changes, including memory and thinking deficits associated with the progression toward dementia.
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