The role of vitamin D in the pathogenesis and treatment of osteoporosis.

It is well recognized that patients with postmenopausal osteoporosis usually exhibit some degree of calcium malabsorption and commonly have low serum concentrations of 1,25-dihydroxyvitamin D (calcitriol). Administration of calcitriol has been shown to normalize calcium absorption in patients with osteoporosis and, over the long term may have a stimulating effect on bone formation. Clinical trials have shown a significant reduction in osteoporotic fractures among calcitriol-treated patients. Hypercalcemia and hypercalciuria are infrequent complications of calcitriol therapy with physiologic doses (0.25 microgram twice daily), and are most commonly related to excessive calcium intake (i.e., > 1000 mg daily).