Older adults with mild cognitive impairment and sleep problems who took at least 5,000 IU of vitamin D daily scored more than 13% higher on a cognitive test than those taking none, according to a preliminary study from Emory University.
The Research
Researchers at Emory University studied 54 older adults with both sleep disturbances and mild cognitive impairment (MCI) — a stage between normal aging and dementia. They compared cognitive performance among participants who reported taking at least 5,000 IU of vitamin D daily, those taking lower doses, and those not taking any. The findings, published in Sleep Medicine on August 23, 2026, showed that the high-dose group scored significantly better on the Montreal Cognitive Assessment (MoCA) — more than 13% higher on average — even after adjusting for other factors like age and education.
Interestingly, lower doses of vitamin D (below 5,000 IU) were not associated with improved scores. The researchers also found no difference between vitamin D2 (from plants/fungi) and D3 (from sun/animal sources) in their association with cognitive performance.
Senior author Victoria Pak, an associate professor at Emory's Nell Hodgson Woodruff School of Nursing, emphasized the importance of timing: "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."
The study was funded by the National Institute on Aging and is the first to examine vitamin D intake specifically in this high-risk group.
Why It Matters
More than 7 million Americans live with Alzheimer's dementia, a number projected to reach 13 million by 2050. Sleep problems are common in Alzheimer's, affecting up to 50% of those with moderate to severe disease, and vitamin D deficiency has been linked to sleep issues and cognitive decline.
This study suggests vitamin D supplementation could be a simple, accessible intervention to support brain health during an early window of cognitive decline. While the findings are preliminary and not proof of cause and effect, they highlight a potentially modifiable factor that deserves further study.
What You Can Do
The study specifically looked at older adults with both sleep problems and MCI, so these results don't apply to everyone. However, maintaining adequate vitamin D levels is important for overall health. If you're concerned about your cognition or sleep, talk to your doctor about checking your vitamin D levels and whether supplementation might be right for you.
Source: ScienceDaily Mind & Brain
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