The lullaby of the sun: the role of vitamin D in sleep disturbance.

Vitamin D is a pro-hormone belonging to the category of the fat-soluble group of vitamins; it is obtained more from solar exposure and in smaller quantities through feeding. Although vitamin D has traditionally been shown to be involved in calcium homeostasis and bone health, recent studies have found a positive association between vitamin D and sleep. In particular, clinical studies in humans indicate that low levels of vitamin D are correlated with poor quality and short sleep duration. The mechanism by which this association is explained is still unclear. However, vitamin D receptors have been found in the brain regions involved in sleep regulation, and vitamin D appears to be involved in regulating the sleep-wake cycle. The current review summarizes the available evidence regarding the association between vitamin D and sleep, focusing on both clinical and preclinical studies.