DETERMINANTS OF THE RATE OF BONE LOSS IN NORMAL POSTMENOPAUSAL WOMEN

Despite a large number of studies assessing relationships between puta tive risk factors and bone density, it is not known which factors infl uence the rate of axial bone loss in normal postmenopausal women. We h ave examined the relationships between the rate of bone loss (Delta BM D) and variables related to calcium metabolism, lifestyle, diet (calci um, sodium, caffeine, and protein), body composition, muscle strength, sex hormones, and spinal osteophytosis in 122 normal postmenopausal w omen participating in a 2-yr prospective randomized placebo-controlled trial of calcium supplementation. Univariate correlation coefficients indicated that Delta BMD at most sites was inversely related to basel ine BMD and positively related to rate of change in body weight (0.10 < r < 0.36) and fat mass (0.11 < r < 0.42) during the study. Lean mass and its rate of change showed no consistent relationship to Delta BMD . There was no correlation between Delta BMD and any of the lifestyle, muscle strength, dietary, or hormonal indices or with the severity of spinal osteophytosis. Multiple regression analysis indicated that Del ta BMD in the total body was directly related to fat mass (P < 0.0001) , the rate of change in fat mass (P < 0.0001), the renal tubular reabs orption of calcium (P < 0.01), and calcium treatment (P < 0.01) and in versely to the initial BMD (P < 0.0001; r(2) = 0.42; P < 0.0001). Simi lar effects were seen throughout the skeleton, although the fraction o f the variance accounted for was less in the subregions, consistent wi th the lower precision of measurement of regional bone density. It is concluded that baseline bone density, fat mass, and renal calcium hand ling are important factors influencing bone loss in normal postmenopau sal women.