"Vitamin D3 acts by regulating calcium and phosphorus intestinal absorption and controls the mobilisation of the electrolytes from bone stores, the later contributing to the synthesis of parathyroid hormone. One of its precursors, 7-dehydrocholesterol, is converted in the skin by UV irradiation (i.e. sunlight) to cholecalciferol. Hence vitamin D deficiency is encountered in populations with little or no sunlight exposure."
"Both vitamin D2 and D3 must undergo two sequential hydroxylations at the carbon-25 position in the liver and kidneys to the active hormonal form 1,25-dihydroxyvitamin D3 (1,25[OH]2D3). The 1α-hydroxylating enzyme is found exclusively in renal tissue (25-OH-D-1α hydroxylase)."
"Both vitamin D2 and D3 must undergo two sequential hydroxylations at the carbon-25 position in the liver and kidneys to the active hormonal form 1,25-dihydroxyvitamin D3 (1,25[OH]2D3). The 1α-hydroxylating enzyme is found exclusively in renal tissue (25-OH-D-1α hydroxylase)."
Expected headings
"Physiology"
"Vitamin D (calciferol) is used to describe a group of five fat-soluble secosteroid vitamins required for the homoeostasis of serum calcium and phosphorus. Vitamin D exists in two main forms (vitamers) in humans: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3)."