The cause of bone loss in postmenopausal osteoporosis - decreased bone formation or increased bone resorption - is controversial. Synthesis of bone-Gla protein (BGP), a specific osteoblast product, is stimulated by 1,25-dihydroxyvitamin D3 [1,25(OH)2D] in vitro. Thus, increases in serum BGP levels during 1,25(OH)2D administration might provide a useful dynamic index of osteoblast function. We compared 14 postmenopausal osteoporotic women with 12 age-matched postmenopausal normal women before and during 6 d of 1,25(OH)2D administration (2.0 μg/d). Serum BGP levels were similar at baseline and increased during treatment in both groups (P < 0.001). However, trend analysis showed a greater (P < 0.01) increase in the osteoporotic women. These data do not support the hypothesis that defective osteoblast function is the major cause of bone loss in postmenopausal osteoporosis.
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