Figure 1.

Proposed schematic diagram for involvement of vitamin D in the regulation of vascular functions. Vitamin D regulates estrogen (E₂) synthesis in gonads by maintaining calcium homeostasis, and E₂ binds to its receptors on endothelial cells and smooth muscle cells to regulate vascular functions. In addition, vitamin D activates vitamin D receptors (VDR) on endothelial cells and vascular smooth muscle cells to regulate endogenous vasodilators, including prostaglandins (PGs), nitric oxide (NO) and calcitonin gene related peptide (CGRP). Vitamin D deficiency results in NO-mediated endothelial dysfunction, and supplementation of vitamin D attenuates this symptom. In addition, vitamin D plays a pivotal role in the down-regulation of renin-angiotensin-aldosterone system (RAAS) by the kidney. Lower vitamin D levels may lead to an impaired RAAS and abnormalities in vascular relaxation that eventually lead to the development of hypertension.