PRINCIPAL COMPONENTS-ANALYSIS OF REGIONAL BONE-DENSITY IN BLACK-AND-WHITE WOMEN - RELATIONSHIP TO BODY SIZE AND COMPOSITION

Black and white women in the United States differ with respect to bone mass and the risk of developing osteoporosis. It has been suggested that greater body size among U.S. blacks may contribute to greater bone density in this group. It is not known whether the fat or lean component contributes more to this relationship. Bone density was measured at seven sites in 161 normal black and white women using single and dual photon absorptiometry. The first principal component accounted for 73% of the variance in the sample and constitutes an index of skeletal mass. The second principal component added another 10% and contrasts the axial and appendicular sites. Both the regional bone densities and the first principal component showed significantly greater bone densities for blacks; adjustment for body size reduced bone mass differences by approximately 50%. Body composition analysis done on a subset of these women indicated that the fat component of body mass may be the more important factor in its effect on bone mass.