Vitamin D Deficiency: Implications in COVID-19 and Schizophrenia

Abstract

Deficiencies in vitamin D can have several etiologies, broadly classified as the following: suboptimal exposure to ultraviolet-B (UV-B) light from sunlight, low dietary intake of vitamin-D or reduced absorption due to gastrointestinal pathologies, reduced production due to liver or kidney disease, pseudo-deficiencies caused by end organ resistance despite normal or elevated vitamin D levels, and medication-induced stimulation of hepatic cytochrome P450 enzymes for which vitamin D is a substrate. Deficiencies in this important vitamin can have several adverse clinical implications such as osteomalacia, osteoporosis, muscle pain, and depression to name a few. More recently, vitamin D has been shown to be involved in modulating various aspects of the immune system. Vitamin D receptors have also been found to be present in certain regions of the brain, especially those involved in schizophrenia. We will discuss the implications of vitamin D deficiency and its immunomodulatory role in the setting of the COVID-19 virus, the proposed cellular and molecular mechanisms of action for vitamin D in the context of schizophrenia, and the clinical outcomes associated with these two pathologies as a function of low vitamin D levels.