Radial and Vertebral Bone Density in White and Black Women: Evidence for Racial Differences in Premenopausal Bone Homeostasis*

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Abstract
The reasons for a different incidence of osteoporotic fractures in white and black women are unknown. Previous racial comparisons of bone mass have been limited by racial differences in body weight and socioeconomic, health, and nutritional status. This cross-sectional study examined bone density in 105 black and 114 white healthy nonobese women, 24-65 yr old, using dual photon absorptiometry of the lumbar spine and single photon absorptiometry of the distal radius. Bone density at both sites was higher in blacks at all ages than in whites. When adjusted for age and body mass index, mean bone density was 6.5% higher in blacks at both spine and radius (P < 0.0001). The cross-sectional rate of decline of vertebral bone density was similar between races; however, radial density increased 3.8%/decade (P = 0.03) in premenopausal blacks under age 46 yr, while it declined 3.2%/decade (P = 0.09) in premenopausal whites. The racial difference in slopes in these premenopausal women is significant (P = 0.002). These findings suggest that attainment of higher peak bone mass and delayed onset of bone loss contribute to the lower incidence of osteoporotic fractures in black women.