Disease Information for Vitamin D deficiency/adult

This fat-soluble vitamin occurs mainly in two forms: ergocalciferol (activated ergosterol, vitamin D2), found in irradiated yeast; and cholecalciferol (activated 7-dehydrocholesterol, vitamin D3), formed in human skin by exposure to sunlight (ultraviolet radiation); In the liver, vitamin D3 is converted to 25(OH)D3, the major circulating form; It passes through the enterohepatic circulation and is reabsorbed from the gut. Principally in the kidneys, it is further hydroxylated to the much more metabolically active form, 1,25(OH)2D3 (1,25-dihydroxycholecalciferol, calcitriol, vitamin D hormone); The main function of vitamin D hormone is to increase calcium absorption from the intestine and promote normal bone formation and mineralization; Metabolic bone disease resulting from vitamin D deficiency is called rickets in children and osteomalacia in adults; Vitamin D deficiency may also be caused by defects in the production of 25(OH)D3 or the action of 1,25(OH)2D3; The deficiency may occur in in hereditary diseases, such as familial hypophosphatemic (vitamin D-resistant) rickets, an X-linked dominant disorder [Type II]; In children, changes include defective calcification of growing bone and hypertrophy of the epiphyseal cartilages; Epiphyseal cartilage cells cease to degenerate normally, but new cartilage continues to form, so that the epiphyseal cartilage becomes irregularly increased in width; Calcification then stops, and osteoid material accumulates around the capillaries of the diaphysis; The cancellous bone of the diaphysis and cortical bone may be resorbed in chronic deficiency; Adequate treatment with vitamin D permits calcium and phosphate deposition through degeneration of the cartilage cells; Osteoid material at the diaphysis ceases to form, and normal endochondral production of new bone is resumed; In adults, the changes are similar but are not confined to the ends of the long bones;aternal osteomalacia can lead to metaphyseal lesions and tetany in the newborn; Young infants are restless and sleep poorly; They have reduced mineralization of the skull (craniotabes), away from the sutures; In older infants, sitting and crawling are delayed as is fontanelle closure, and there is bossing of the skull and costochondral beading (rachitic rosary); In children aged 1 to 4 yr, epiphyseal cartilages at the lower ends of the radius, ulna, tibia, and fibula enlarge; kyphoscoliosis develops, and walking is delayed; In older children and adolescents, walking is painful, and in extreme cases, such deformities as bowlegs and knock-knees develop; Rachitic tetany is caused by hypocalcemia and may accompany infantile or adult vitamin D deficiency;

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