High doses of vitamin D may improve cognitive functions

The study involved 54 adults who exhibited two characteristic signs of early‑stage dementia: sleep disorders and mild cognitive impairment (MCI). Participants who took at least 5,000 IU of vitamin D daily demonstrated better results in cognitive tests compared to those who did not take such doses.

The results, published in the journal Sleep Medicine, showed that people who reported taking 5,000 IU or more of vitamin D per day scored, on average, more than 11 % higher on the Montreal Cognitive Assessment (MoCA) scale, even after accounting for the influence of other factors. The MoCA is a widely used tool for identifying the risk of developing dementia; it allows for the assessment of memory and thinking skills. At the same time, lower daily doses of vitamin D were not associated with improved cognitive performance.
According to researchers, the timing of intervention also plays an important role. Mild cognitive impairment represents an intermediate stage between normal age‑related decline in cognitive abilities and dementia.

As the authors note, in older people who simultaneously experience sleep disorders and MCI, there may be a critical window of opportunity for intervention: cognitive changes are already beginning to manifest, but there is still a chance to support brain health.

Another important conclusion of the study concerns the form of vitamin D: cognitive outcomes did not differ depending on whether participants took vitamin D2 (usually obtained from plants or fungi) or D3 (which is produced in the body under the influence of sunlight or is obtained from animal‑based foods).

Vitamin D is an important nutrient that is necessary not only for the functioning of muscles and the nervous system but also affects sleep quality and sleep–wake cycles. At the same time, about half of patients with moderate to severe Alzheimer’s disease experience sleep disorders, which indicates a bidirectional relationship between sleep deprivation and cognitive decline. Although vitamin D deficiency has previously been linked to sleep problems, such as insomnia and frequent nighttime awakenings, this preliminary study is the first to assess the relationship between taking vitamin D supplements and cognitive function specifically in a high‑risk group combining mild cognitive impairment and sleep disorders.

The authors say that the preliminary data obtained do not necessarily mean that high doses of vitamin D can be recommended as a means of preventing or treating cognitive impairments. Nevertheless, identifying accessible and modifiable factors (such as vitamin D intake) at the early stages of cognitive decline may become increasingly important as the prevalence of Alzheimer’s disease grows.