Vitamin D: A Pleiotropic Hormone with Possible Psychotropic Activities

Background: After the recognition of the efficacy of cod–liver oil in rickets at the end of the eighteenth century, and the isolation and synthesis of the liposoluble vitamin D in 1931, its mode of actions and functions were deeply explored. Biochemical studies permitted to identify five forms of vitamin D, called D1, D2, D3, D4 and D5, differing in ultrastructural conformation and origin, with vitamin D2 (ergocalciferol) and D3 (cholecalciferol) representing the active forms. In the last decades especially, a constantly increasing bulk of data highlighted how vitamin D could regulate several activities and processes. Aims: The aim of the present paper was to review and comment on the literature on vitamin D, with a focus on its possible role in the pathophysiology of neuropsychiatric disorders. Discussion: Available literature indicates that vitamin D regulates a variety of processes in humans and in the central nervous system. Vitamin D deficiency is associated with an enhanced pro-inflammatory state, and formation of Aβ oligomers that might contribute to the cognitive decline typical of the elderly age and, perhaps, dementia. More in general, vitamin D is supposed to play a crucial role in neuroinflammation processes that are currently hypothesized to be involved in the pathophysiology of different psychiatric disorders, such as major depression, bipolar disorders, obsessive-compulsive disorders and psychosis. Conclusion: It is conceivable that vitamin D supplementation might pave the way towards “natural” treatments of a broad range of neuropsychiatric disorders, or at least be useful to boost response to psychotropic drugs in resistant cases.