Vitamin D: Higher Dose Linked to Better Cognition

A team of researchers at Emory University in Atlanta has published a study that links a high daily dose of vitamin D to a better memory test score in people who have both a sleep disorder and mild cognitive impairment, two early warning signs of dementia. The paper appeared in the journal Sleep Medicine, under the identifier 10.1016/j.sleep.2026.108960. The authors themselves stress that the finding is preliminary, but the subject carries its own urgency: more than 7 million people in the United States currently live with Alzheimer’s dementia, and that number is expected to climb to nearly 13 million by 2050.

Srpske novine previously covered an attempt to flag dementia risk with artificial intelligence, in a piece on AI based brain age assessment. This new study comes at the question from the opposite direction: instead of expensive imaging, it asks whether something as accessible as a dietary supplement has any bearing on cognition at this early stage, when a sleep disorder and mild cognitive impairment are already present but a dementia diagnosis has not yet been made.

What the study actually measured

The study enrolled 54 adults who had both a sleep disorder and mild cognitive impairment (MCI), a condition medicine treats as an intermediate stage between normal brain aging and dementia. The team assessed cognition with the Montreal Cognitive Assessment (MoCA), a standard screening test for memory and thinking that is also used to gauge dementia risk. Vitamin D intake was based on what participants reported about their own supplement use, not on blood measurements, a limitation the authors point out themselves.

Participants who reported taking 5,000 international units (IU) or more of vitamin D daily scored more than 13 percent higher on the MoCA test than those who took no supplement at all. The difference held even after the researchers adjusted for participants’ age, sex, body mass index and education. Lower daily doses, below that threshold, showed no association with a better score, the effect appeared only above the 5,000 IU mark. There was no difference in cognitive benefit between the D2 form, mostly derived from plants and mushrooms, and D3, which the body produces from sunlight and also gets from animal based foods.

Why the timing of intervention matters

The researchers single out the stage of life at which the effect was measured, because mild cognitive impairment is a condition in which changes are just beginning, but there is still a chance to influence the brain.

“In older adults who have both a sleep disorder and mild cognitive impairment, this may represent a key window for intervention.”

The line is attributed to Victoria Pak, the study’s senior author and an associate professor at Emory’s Nell Hodgson Woodruff School of Nursing, in a statement from the university. Pak also explains why she considers this particular kind of measure significant.

“Recognizing accessible and modifiable factors, such as taking a vitamin D supplement, in the earlier stages of cognitive decline could become increasingly important.”

Alongside Pak, the paper is co-authored by Sirui Zhou, Paul Sudeshna, Lynn Marie Trotti and Donald Bliwise, also of Emory University. The research was funded by the National Institute on Aging, part of the National Institutes of Health, through grants numbered R01AG097853-01 and R61AG080606.

Vitamin D is a nutrient important for muscle and nerve function, and it has also been linked to sleep quality. Sleep disturbances are a common companion of Alzheimer’s dementia: half of people with moderate to severe forms of the disease report sleep problems, which points to a two way relationship between poor sleep and declining cognition. Earlier research had already linked vitamin D deficiency to insomnia and more frequent nighttime waking, but the authors say this study is the first to examine the relationship between vitamin D and cognition specifically in people who have both a sleep disorder and mild cognitive impairment at the same time.

What this study does not prove

This is an observational study, not a controlled clinical trial: the researchers recorded what people were already doing, they did not randomly assign anyone to a group that received vitamin D and a group that did not. A design like that produces an association, not proof of cause and effect, and the sample of 54 people is small for a firmer conclusion. The authors explicitly call this an initial study that needs larger trials before the finding can be confirmed.

There is also a warning the authors put front and center themselves: the dose at which they saw the effect, 5,000 IU daily, is higher than the upper limit current guidelines consider safe, which sits below 4,000 IU daily. Excess vitamin D intake carries a risk of toxicity, so the finding is not a call to exceed the recommended dose on one’s own, but a reason to run larger, controlled studies before drawing any recommendation for wider use out of this pattern.