Adults taking at least 5,000 IU of vitamin D a day scored more than 13% higher on the Montreal Cognitive Assessment than those taking none, according to new research from Emory University published in Sleep Medicine. The difference held after researchers adjusted for other factors. Lower daily doses showed no such association.
The study followed 54 adults who had both sleep disturbances and mild cognitive impairment - two conditions that can signal the earliest stages of dementia. That makes the group a useful population to watch, since these are people whose trajectory is still uncertain and who may be most likely to benefit from anything that slows cognitive decline. The MoCA itself is a standard screening tool clinicians use to gauge memory, thinking, and dementia risk, so a 13% gap on it is not a trivial statistical artifact.
Why the dose threshold matters: the benefit appeared only at the higher intake level. Participants reporting smaller daily amounts of vitamin D did not show better scores than those taking none at all. That pattern, if it holds up in larger work, would matter for how future trials are designed, since studies testing modest doses might miss an effect that only emerges higher up.
The scale of the problem gives this line of research urgency. More than 7 million Americans currently live with Alzheimer's dementia, and that figure is projected to approach 13 million by 2050. But 54 participants is a small sample, and the study links reported supplement intake to test scores rather than tracking what happens to people over time - it cannot establish that vitamin D caused the better performance.