Vitamin D is known not only for its essential role in calcium homeostasis and bone health but also for maintaining a healthy mind. A number of recent studies, in fact, have demonstrated a correlation between vitamin D deficiency and psychiatric illness.
In addition to all its other functions, vitamin D acts as a potent neurosteroid hormone, critical to brain development and normal brain function; it is known for its anti-inflammatory properties, which are able to affect many aspects of human health.
The vitamin D receptor, which mediates many of its biological actions, has been found throughout the body, including in the central nervous system. Vitamin D deficiency is common in patients with serious mental illnesses, such as depression, schizophrenia and neurocognitive disorders.
Several risk factors, such as genetic and environmental factors, season of birth, latitude and migration, have been linked to vitamin D deficiency and can explain, at least in part, the association between hypovitaminosis D and mental illness.
The causal link between hypovitaminosis D and mental illness is probably bi-directional; mental illness increases the risk of hypovitaminosis D, and hypovitaminosis D increases the risk of developing mental illness.
The biological mechanism at the base of the relationship between hypovitaminosis D and mental illness is most likely related to vitamin D action on the regulation of inflammatory and immunological processes, which in turn can act as mediators or modulators for the development of clinical symptoms and/or treatment response.
Our review has found sound proof of a significant association between mental illness and vitamin D deficiency, yet it has also highlighted the need to further investigate, in future studies, the direction of the causal link of the relationship between vitamin D deficiency and other specific variables that are involved. This would be important in order to determine the best prevention and treatment strategies for hypovitaminosis D in patients with mental illnesses such as depression, psychosis and neurocognitive disorders.