Bone mass and markers of bone and calcium metabolism in postmenopausal women treated with 1,25-dihydroxyvitamin D (calcitriol) for four years

To evaluate the long-term effect of calcitriol treatment on bone mineral de nsity (BMD) of the femoral neck and lumbar spine and the parameters of calc ium and bone metabolism in elderly women, 55 healthy, postmenopausal women, all aged 66 years, were enrolled in the study. Eighteen started a 4-year s upplementation with 0.5 mu g of calcitriol daily and 37 served as controls. Calcium intake of all the subjects was adjusted to 800 mg daily. In 4 year s femoral neck BMD increased by 3.0% in the calcitriol group, but decreased by 1.6% in the control group (P = 0.009). The respective changes in lumbar spine BMD were +2.3% and +0.9% (P = 0.067). Two years' treatment with calc itriol increased the intestinal absorption of strontium by 57% (P < 0.001), doubled the urinary excretion of calcium (P < 0.001), and decreased the me an parathyroid hormone (PTH) level by 32% (P < 0.01). In the calcitriol gro up the marker of bone formation, serum osteocalcin, decreased by 27% (P < 0 .01), and the marker of bone resorption, serum C-telopeptide of type I coll agen (CTx), by 33% (P = 0.05) after 2 years. In two subjects the calcitriol dose had to be reduced because of hypercalciuria. We conclude that calcitr iol treatment increases bone mass at the femoral neck and lumbar spine, the increases being maintained for up to 4 years. The gain in bone mass result s from reduced bone turnover which is partly a consequence of the enhanced intestinal absorption of calcium and suppressed serum PTH levels.