1,25-Dihydroxyvitamin D3: Short-and long-term effects on bone and calcium metabolism in patients with postmenopausal osteoporosis

Abstract

We evaluated the effects of therapy with a small dose (0.5 μg/day) of 1,25-dihydroxyvitamin D3 in 12 previously untreated patients with postmenopausal osteoporosis. Combined radiocalcium kinetic and balance studies showed that at base line, net calcium absorption (mean ± SEM) was low (7 ± 3%), calcium balance was negative (-59 ± 22 mg/day), and bone resorption rate (297 ± 40 mg/day) exceeded bone formation rate (239 ± 36 mg/day). After short-term therapy (6-8 months), calcium absorption was normal (27 ± 3%. P<0.001 for difference from base line), calcium balance had improved (+2 ± 26 mg/day, P<0.05), and bone resorption rate (195 ± 35 mg/day, P<0.01) had decreased more than bone formation rate (197 ± 26 mg/day, NS). Compared with base-line values, after long-term therapy (2 years) the increased level of calcium absorption was maintained (27 ± 3%, P<0.001), but calcium retention declined to a level intermediate (-27 ± 24 mg/day, NS) between base-line and short-term treatment values, and both bone resorption rate (294 ± 33 mg/day, NS) and bone formation rate (267 ± 34 mg/day, NS) increased. Urinary hydroxyproline excretion was lower than before treatment (26.3 ± 2.0 mg/day) after both short-term (21.1 ± 1.6 mg/day, P<0.001) and long-term (22.0 ± 1.8 mg/day, P<0.01) treatments. Trabecular bone volume was 11.3 ± 1.0% at base line and increased to 16.0 ± 1.2% (P<0.01) after long-term treatment. By contrast, the eight patients studied before and after 6-8 months of placebo treatment had no significant change in any variable.