Vitamin D (vitD) is known for its essential role in calcium homeostasis and bone health. VitD is made endogenously in the skin from UVB radiation from sunlight. VitD is now considered as a potent neurosteroid hormone, critical to brain development and normal brain function, and is known for its anti-inflammatory property affecting various aspects of human health. VitD ligand-receptor, a receptor that mediates much of vitD's biological actions, has been found throughout the body including the central nervous system. VitD deficiency is common in patients with severe mental illness such as schizophrenia. Schizophrenia is a debilitating chronic mental illness characterised by positive symptoms, such as hallucinations and delusions, and negative symptoms including flat affect and lack of motivation. Several environmental risk factors for schizophrenia, such as season of birth, latitude and migration, have been linked to vitD deficiency. Recent studies have suggested a potential role of vitD in the development of schizophrenia. For example, neonatal vitD status is associated with the risk of developing schizophrenia in later life obesity, insulin resistance, diabetes, hyperlipidaemia and cardiovascular disease, which are commonly seen in patients with schizophrenia. It has been well established that vitD deficiency is related to these metabolic problems. The biological mechanism is most likely related to vitD's action on the regulation of inflammatory and immunological processes, consequently affecting the manifestation of clinical symptoms and treatment response of schizophrenia. Potential benefits of vitD supplementation to improve schizophrenia symptoms as well as physical health in patients with schizophrenia should be further explored in future studies.
Introduction
Vitamin D (vitD), the 'sunshine' vitamin, is widely known for its essential role in calcium absorption and bone health. VitD is created in mammals after the epidermis comes into contact with UVB light. UVB radiation catalyses the conversion of 7-dehydrocholesterol to previtamin D3 in the skin, which is then quickly converted into vitamin D3 (cholecalciferol) by the body. 25-hydroxyvitamin D [25(OH)D], the main circulating form of vitD, is used by clinicians to measure vitD levels in the body. VitD is also obtained through dietary sources. Fatty fish, fungus and eggs naturally contain high levels of vitD. In many countries, cereal, milk and other everyday foods are fortified with vitD. VitD is also readily available as a dietary pill. However, since most individuals lack the necessary amount of exposure to UVB light and do not consume enough dietary vitD, vitD deficiency has become a global pandemic. While vitD has long been associated with bone health and related diseases, research in the past decade has uncovered its widespread effects on other aspects of the human body. Studies have identified links between vitD and a multitude of conditions including various cancers, autoimmune diseases, cardiovascular diseases, infectious diseases and mental disorders.
Studies have unveiled the presence of vitD, vitD receptors (VDR) and related enzymes (CYP 27B1, CYP 24A1) in various regions of the brain, leading researchers to establish vitD as a neuroactive/neurosteroid hormone critical to brain development and normal brain function. Furthermore, VitD's possible role in depression has led researchers to explore its potential benefits in other mental illnesses.
Schizophrenia is a severe and debilitating mental illness characterized by chronic positive (hallucinations, delusions) and negative symptoms (lack of motivation, speech issues).
