Vitamin D 1, 25 dihydroxy

Vitamin D3 is produced by the skin endogenously .Vitamin D2 is primarily a plant product and is in many nutritional vitamin supplements. Both Vitamin D2 and D3 are biologically active. Vitamin D is converted into 25 hydroxy vitamin D (25-OH D) in the liver. In kidney, it is converted into 1,25 dihydroxy vitamin D, which is biologically active.1,25-dihydroxy vitamin D is the most potent vitamin D metabolite. It stimulates calcium absorption in the intestine and its production is tightly regulated through concentrations of serum calcium, phosphorus, and parathyroid hormone.1,25-Dihydroxy vitamin D levels may be high in primary hyperparathyroidism and in physiologic hyperparathyroidism secondary to low calcium or vitamin D intake. Some patients with granulomatous diseases (e.g. sarcoidosis) and malignancies containing nonregulated 1-alpha hydroxylase in the lesion may have elevated 1, 25-dihydroxy vitamin D levels and hypercalcemia. 1, 25-dihydroxy vitamin D levels are decreased in hypoparathyroidism and in chronic renal failure.