Serum 25-hydroxyvitamin D concentrations, sleep characteristics and the risk of incident dementia

Serum 25-hydroxyvitamin D concentrations have been associated with the risk of dementia, but the results are inconsistent. Previous studies have reported that vitamin D metabolism is related to sleep characteristics. We investigated the association between serum 25-hydroxyvitamin D concentrations and the risk of dementia, as well as whether sleep characteristics and sleep patterns modified this association.

In this prospective population-based cohort study, serum 25-hydroxyvitamin D concentrations were measured. Sleep characteristics, including sleep duration, chronotype, sleeplessness, snoring, and daytime sleepiness, were integrated to generate an overall sleep pattern. We used a multivariable adjusted Cox proportional hazards regression model to evaluate the association of serum 25-hydroxyvitamin D concentrations with the risk of incident dementia.

Over a median follow-up of 13.7 years, there were 7030 cases of all-cause dementia, including 3089 of Alzheimer's disease and 1539 of vascular dementia in the cohort of 366,160 participants. Higher concentrations of serum 25-hydroxyvitamin D were associated with a lower risk of all-cause dementia, Alzheimer's disease and vascular dementia. We found a statistically significant interaction of modest magnitude between serum 25-hydroxyvitamin D concentrations and sleep patterns with the risk of vascular dementia (P interaction = 0.04). Among the sleep characteristics, an interaction was found between serum 25-hydroxyvitamin D concentrations and daytime sleepiness in their effect on the risk of vascular dementia (P interaction = 0.03). The protective hazard ratios for vascular dementia were more pronounced in individuals with low daytime sleepiness than in those with high daytime sleepiness.

Serum 25-hydroxyvitamin D concentrations were inversely associated with the risks of all-cause dementia, Alzheimer's disease and vascular dementia. Sleep characteristics, particularly daytime sleepiness, may modify the association between serum 25-hydroxyvitamin D concentrations and the risk of vascular dementia.