Non-classical role of vitamin D (Homo sapiens)

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Vitamin D is known for its participation in various skeletal and non-skeletal muscle homeostasis. In addition to Calcium (Ca²⁺) and phosphorous (P) absorption, its association with CVD, hypertention, cancer, obesity, diabetes and immune system has been reported. It actively participates in the regulation of cardiovascular system through Renin Angiotensin Aldosterone System (RAAS). Renin is secreted by the kidney and it activates the formation of angiotensin II that leads to the decreased production of nitric oxide (NO) and increased endothelial vascular dysfunction (Pérez-Hernández et al., 2016). Vitamin D causes the insulin release, facilitates muscle contraction and glucose uptake by enhancing the activity of glucose transporter 4 (GLUT4) channels in the cells (Berridge, 2017) and reduces the aldosterone . From last few years vitamin D has gained special attention as immunomodulatory agent. The immunologic cells such as B cells, T cells, and antigen presenting cells express vitamin D receptors on their cells as well as are capable of synthesizing vitamin D metabolites especially calcitriol. The beneficial effects of vitamin D are linked with both innate and adaptive immune systems. During vitamin D deficiency an unwanted production of pro-inflammatory cytokines cause atherosclerotic lesions and atherogenesis. These conditions lead to increased vasoconstriction and decreased vasodilation, endothelial dysfunction, and alleviated nitric oxide formation. Furthermore, the expression of angiotensin-converting enzyme 2 (ACE2; responsible for the retrospective production of Ang1-7 form Ang II) is also reduced in vitamin D deficient subjects. Such individuals are more vulnerable to infectious diseases, especially, recent pandemic of COVID-19 (Malek Mahdavi, 2020).