BODY-WEIGHT VERSUS BODY-FAT DISTRIBUTION, ADIPOSITY, AND FRAME SIZE AS PREDICTORS OF BONE-DENSITY

Weight is strongly associated with bone mineral density (BMD), but the mechanism of this effect is not well understood. Weight, height, hip- waist ratio, elbow breadth, adiposity, and BMD were measured in 6705 o lder women participating in the Study of Osteoporotic Fractures. Adipo sity was measured by bioelectric impedance and BMD by single-photon (p roximal and distal radius and calcaneus) and dual-energy x-ray absorpt iometry (lumbar spine and proximal femur). Age-adjusted associations b etween weight and BMD were robust at all sites (R(2) = 5.9-20.4%), but the addition of other anthropometric variables to the model only marg inally improved the association. Adiposity explained a substantial fra ction of the effect of weight on BMD, particularly at weight-bearing s ites (36-62%). On the other hand, weight explained virtually all the v ariability of adiposity on BMD at weight-bearing sites (81-100%). At t he radial measurement sites, adiposity had more substantial independen t contributions. Weight did not seem to influence the relationship bet ween BMD and age. In sum, at weight bearing-sites, the preponderance o f the effect of weight on BMD is a direct result of mass effects rathe r than adiposity, whereas at non-weight-bearing sites, adiposity exert s more important effects, potentially mediated by metabolic factors.