![]() ![]() Vitamin D deficiency impairs hypertrophic cartilage and bone mineralization, leading to rickets in children and osteomalacia in adults. ![]() Calcitriol is a potent stimulator of bone resorption, by increasing the expression and production of RANKL by osteoblasts. Calcitriol stimulates intestinal trans-epithelial transport of calcium and phosphate through both genomic and non-genomic mechanisms. The latter step is stimulated by PTH, IGF-I and by low calcium or phosphate intakes or concentrations. Synthesized in the skin under the influence of UV light, vitamin D (cholecalciferol) undergoes a first hydroxylation in position 25 in the liver, leading to 25-hydroxyvitamin D (calcifediol), and a second one in position 1 in the kidney, leading to the active metabolite 1,25-dihydroxyvitamin D (calcitriol). Vitamin D is an important regulator of calcium and phosphate homeostasis.
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