BODY-COMPOSITION AND BONE-MINERAL DENSITY IN PREMENOPAUSAL AND EARLY PERIMENOPAUSAL WOMEN

Body composition appears to be an important determinant of bone minera l density (BMD). BMD at the femoral neck, lumbar spine, and whole-body and the whole-body soft-tissue composition were measured cross-sectio nally in 334 healthy premenopausal and early perimenopausal women, age d 44-50 years, using a Hologic QDR densitometer. Correlations between. lean mass and BMD at the hip, spine, and whole-body were greater (r = 0.40, r = 0.44, and r = 0.45, respectively, p < 0.0001) than those fo r fat mass (r = 0.19, r = 0.16, and r = 0.16, respectively, p < 0.01). There was a significant linear trend in femoral BMD from the lowest t o highest category of lean mass (0.75 +/- 0.10 g/cm(2), 0.80 +/- 0.10 g/cm(2), and 0.86 +/- 0.09 g/cm(2), p < 0.0001). Similar trends were d emonstrated for spinal and whole-body density. For categories of fat m ass, there was a significant linear trend at the hip (0.78 +/- 0.10 g/ cm(2), 0.79 +/- 0.10 g/cm(2), and 0.83 +/- 0.10 g/cm(2), p = 0.0106), but not at the spine or whole-body. There was a 5.00% (3.62, 6.38; 95% confidence limits) difference in hip BMD per unit (standard deviation ) of lean mass, while only a 0.73% (-0.66, 2.11) difference in hip BMD per unit (SD) of fat mass. Differences in BMD were examined by catego ries of lean and fat mass (low, medium, high) for a total of nine poss ible combinations of lean and fat measures. BMD at the hip, spine, and whole-body were significantly higher in those with high lean mass tha n in those with low lean mass, irrespective of fat mass. Women with hi gh lean/low fat had similar hip, spinal, and whole-body BMD as those w ith high lean/high fat, despite their significantly lower body weight (62.5 +/- 3.3 kg vs 85.7 +/- 5.4 kg, respectively, p < 0.0001). In pre menopausal and early perimenopausal women, body weight alone may not b e associated with increased bone mass unless a significant proportion of that weight is comprised of lean mass. The stronger association bet ween lean mass and BMD than that for fat mass may be attributed to dif ferences in determinants of lean mass, such as exercise, lifestyle fac tors, estrogen levels, or a combination of these factors.