The effects of race and body habitus on bone mineral density of the radius, hip, and spine in premenopausal women

The incidence of osteoporosis and fractures of the hip are diminished in blacks and in obese subjects. To determine whether bone mass is increased in them, bone mineral density (BMD) of the lumbar spine, trochanter, and femoral neck was measured by dual photon absorptiometry in 89 nonobese white and 51 nonobese black women, all of whom were within 30% of their ideal body weight and between the ages of 20 and 50 yr, and in 21 obese white women and 21 obese black women, all of whom weighed 30% on more than their ideal body weight and were in the same age range. The BMD of the mid radius was also measured by single photon absorptiometry. The mean BMD of the mid radius was higher in black than in white nonobese women [0.73 ± 0.01 (±se) vs. 0.70 ± 0.01 g/cm²; P < 0.01] and was not altered by obesity in either group. The mean BMD was higher in the black than in the white nonobese women at the lumbar spine (1.23 ± 0.02 vs. 1.16 ± 0.01 g/cm²; P < 0.01), trochanter (0.78 ± 0.02 vs. 0.72 ± 0.01 g/cm²; P < 0.01) and femoral neck (0.96 ± 0.02 vs. 0.90 ± 0.02 g/cm²; P < 0.02). The mean body weight was higher in the obese than in the nonobese white women (92 ± 2 vs. 61 ± 1 kg; P < 0.001) and black women (94 ± 3 vs. 63 ± 1 kg; P < 0.001). The mean BMD was higher in the obese than in the nonobese white women at the lumbar spine (1.24 ± 0.03 g/cm²; P < 0.05), trochanter (0.89 ± 0.04; P < 0.001), and femoral neck (0.99 ± 0.03; P < 0.01) and was higher in the obese than in the nonobese black women at the lumbar spine (1.33 ± 0.03 g/cm²; P < 0.01), trochanter (0.88 ± 0.04 g/cm²; P < 0.05), and femoral neck (1.04 ± 0.03 g/cm²; P < 0.05). Multivariate regression analysis revealed positive correlations between body weight and BMD at each of the 3 weightbearing sites, but not at the mid radius, in both the black women and white women. These results provide evidence that 1) the BMDs of the radius, hip, and spine are higher in black than in white nonobese premenopausal women, and 2) the BMDs of the hip and spine, but not that of the radius, are higher in obese than in nonobese premenopausal women, both black and white. Thus, a higher BMD may account for the lower incidence of osteoporosis and fractures of the hip in black and in obese women.