| [ Summary ] |
Vitamin D is an essential nutrient for bone health, and its deficiency causes rickets or osteomalacia, characterized by calcification defect in the bone. Moreover, vitamin D maintains serum calcium concentration together with parathyroid hormone (PTH), and its deficiency leads to hypocalcemia. Vitamin D also increases serum phosphate levels. This is the counteracting effect of PTH and fibroblast growth factor 23. Vitamin D is activated to 1,25-dihydroxyvitamin D [1,25(OH)2D] by two steps of hydroxylation that occurs in the liver and kidney. Then, 1,25(OH)2D binds to vitamin D receptor (VDR)， which acts as a ligand-dependent transcription factor. Vitamin D exerts most of its function by binding to VDR. An increase in vitamin D deficiency has been reported worldwide, and action plans to eliminate vitamin D deficiency have been proposed. |