Vitamin D aids in the absorption of calcium and has central roles in bone formation and maintenance, hypertension, cancer, and immunity. 1-hydroxy Vitamin D2 is a synthetic prodrug of the active 1,25-dihydroxy vitamin D2 , as well as of other active metabolites. It is used to suppress the synthesis and secretion of parathyroid hormone in secondary hyperparathyroidism, an action which requires vitamin D receptor. 1-hydroxy Vitamin D2 is effective in stimulating bone growth and, in combination therapy with angiotensin receptor blockers, ameliorates albuminuria and glomerulosclerosis associated with diabetic nephropathy. It also inhibits the growth of certain blastomas and prostate cancer cells.