Vitamin D and sleep regulation: is there a role for vitamin D?

BACKGROUND: Vitamin D exerts multiple pleiotropic effects beyond its role in calcium-phosphate metabolism. Growing evidence suggest an association between hypovitaminosis D and sleep disorders, thus increasing the interest on the role of this vitamin in the regulatory mechanisms of sleep-wake cycle. OBJECTIVE: To explore and summarize the current knowledge about the role of vitamin D in sleep regulation and the impact of vitamin D deficiency on sleep disorders. METHODS: The main regulatory mechanisms of vitamin D on sleep are explained. The literature was scanned to identify clinical trials and correlation studies showing an association between vitamin D deficiency and sleep disorders. RESULTS: Vitamin D receptors and the enzymes that control its activation and degradation are expressed in several areas of the brain involved in sleep regulation. Vitamin D is also involved in the pathways of production of Melatonin, the hormone involved in the regulation of human circadian rhythms and sleep. Furthermore, vitamin D can affect sleep indirectly through non specific pain disorders, correlated with alterations in sleep quality, such as restless legs syndrome and obstructive sleep apnea syndrome. CONCLUSIONS: Vitamin D has both a direct and an indirect role in the regulation of sleep. Although vitamin D deficiency has been associated to sleep disorders, there is still scant evidence to concretely support the role of vitamin D supplementation in the prevention or the treatment of sleep disturbances; indeed more intervention studies are needed to better clarify these aspects.