In most cases studied, the effect is to activate transcription, but situations are also known in which vitamin D suppresses transcription. The vitamin D receptor forms a complex with another intracellular receptor, the retinoid-X receptor, and that heterodimer is what binds to DNA. Like the receptors for other steroid hormones and thyroid hormones, the vitamin D receptor has hormone-binding and DNA-binding domains. Calcitriol binds to intracellular receptors that then function as transcription factors to modulate gene expression. It promotes renal reabsorption of calcium, increases intestinal absorption of calcium and phosphorus, and increases calcium and phosphorus mobilization from bone to plasma.Ĭalcidiol is transformed in the kidney by 25-hydroxyvitamin D3-1-(alpha)-hydroxylase to calcitriol, the active form of vitamin D3. Vitamin D plays an important role in maintaining calcium balance and in the regulation of parathyroid hormone (PTH). Common causes of vitamin D deficiency include genetic defects in the vitamin D receptor, severe liver or kidney disease, and insufficient exposure to sunlight. Both rickets and osteomalacia reflect impaired mineralization of newly synthesized bone matrix, and usually result from a combination of inadequate exposure to sunlight and decreased dietary intake of vitamin D. Deficiency in adults leads to the disease osteomalacia. The classical manifestations of vitamin D deficiency is rickets, which is seen in children and results in bony deformaties including bowed long bones. Vitamin D3 is a steroid hormone that has long been known for its important role in regulating body levels of calcium and phosphorus, in mineralization of bone, and for the assimilation of vitamin A. Hidroferol also has mineralizing properties.Ĭalcidiol is the precursor of vitamin D3. It is effective in the treatment of rickets and osteomalacia, both in azotemic and non-azotemic patients.

It is produced in the liver and is the best indicator of the body's vitamin D stores. The major circulating metabolite of vitamin D3 (cholecalciferol).

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