RESOLVING THE LEDGER
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0 Share Newsweek is a Trust Project member See more of our trusted coverage when you search. Prefer Newsweek on Google to see more of our trusted coverage when you search. A vitamin supplement already taken by millions of people could have an unexpected link to brain health, according to new research focused on older adults at risk of dementia.
Researchers from Emory University found that higher-dose vitamin D supplementation was associated with better cognitive performance among adults experiencing both mild cognitive impairment (MCI) and sleep disturbances, two factors linked to an increased risk of Alzheimer's disease.
Mild cognitive impairment is often considered an intermediate stage between normal age-related memory changes and dementia.
Sleep problems are also common among people with MCI, affecting nearly half of patients and potentially increasing the risk of further cognitive decline .
"Our findings give us an interesting lead on the relationship between vitamin D supplement intake and cognitive performance, particularly in people with mild cognitive impairment and sleep disturbances," Victoria Pak, associate professor at Emory University's Nell Hodgson Woodruff School of Nursing, told Newsweek .
When cognitive symptoms are already developing, pinpointing a potentially modifiable factor is especially significant, Pak added.
The study involved 54 adults aged 50 and older who had both sleep disturbances and diagnosed or suspected MCI.
Researchers assessed participants' cognitive function using the Montreal Cognitive Assessment (MoCA), a widely used screening tool for memory and thinking skills.
They also collected information on vitamin D supplement use , including dosage and type.
After accounting for factors including age, sex, body mass index and education level, the researchers found that participants who reported taking 5,000 international units (IU) or more of vitamin D daily performed significantly better on cognitive testing than those who did not take vitamin D supplements.
Lower doses showed no significant association with cognitive performance.
The researchers concluded that high-dose vitamin D supplementation was associated with better overall cognition in this particular group of older adults.
However, they stressed that the findings should be interpreted with caution.
The number of participants taking 5,000 IU or more each day was relatively small, and the study was observational rather than a clinical trial designed to prove cause and effect.
In other words, the findings do not prove that vitamin D improves memory or prevents dementia.
It is possible that people with better cognitive function are also more likely to engage in health-conscious behaviors, including taking supplements.
The researchers specifically noted that reverse causation could not be ruled out.
The study also found no significant difference between vitamin D2 and vitamin D3, suggesting that dose may be more important than the type of supplement consumed.
Scientists say there are several possible biological explanations for the link. Previous research has suggested vitamin D may help regulate inflammation , while poor sleep has been associated with increased inflammatory activity and worse cognitive outcomes.
Neuroinflammation has also been proposed as one mechanism connecting sleep disturbances and cognitive decline .
The researchers said it remains unclear why the association was seen only among participants who reported higher vitamin D supplement intake.
To explore the finding further, Pak said the next step will be a randomized clinical trial to test vitamin D supplementation directly.
Such a study could help determine whether vitamin D has a causal effect on cognitive performance and whether it may offer a potential strategy for supporting cognitive health.
Despite the promising results, larger studies are needed.
"Since this was an observational study, we’re not yet at the point of recommending high-dose vitamin D," Pak said. "Whether supplementation is appropriate depends on the individual, so anyone considering it should talk with their healthcare provider about what’s right for them."
Zhou S, Sudeshna P, Trotti LM, Bliwise D, Pak V. Vitamin D supplement intake is associated with better cognition in persons with sleep disturbance and mild cognitive impairment. Sleep Med. 2026 Oct;146:108960. doi: 10.1016/j.sleep.2026.108960.
Contact Newsweek editors on this story: Kara Dolman and Emma Lee-Sang
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