Higher fracture risk in White versus Black women is partly explained by lower BMD and worse bone microarchitecture in White women. However, whether rates of decline in bone density, microarchitecture and strength differ between postmenopausal Black and White women is unknown. Further, factors that influence rates of age-related bone microarchitecture deterioration remain ill-defined. Thus, over 6.7 years, we measured longitudinal changes in peripheral volumetric bone mineral density (vBMD), microarchitecture and strength at the distal radius and tibia using high-resolution peripheral quantitative computed tomography (HR-pQCT) in postmenopausal Black (n=80) and White (n=137) women participating in the Study of Women’s Health Across the Nation (SWAN). We assessed whether age-related changes in vBMD and microarchitecture were influenced by body weight, body composition, and/or weight change.
We found that at the radius, whereas White women appeared to have slightly greater rates of loss in total vBMD, cortical bone volume and porosity than Black women, those differences were attenuated after adjusting for clinical covariates. At the tibia, Black and White women had similar rates of bone loss. Independent of race and other clinical covariates, women with the lowest baseline body weight experienced the greatest decline in total and trabecular vBMD at the radius. Further, women who lost weight over the follow-up period had higher rates of bone loss, particularly at the tibia, compared to those who maintained or gained weight. Higher baseline total body fat mass was also protective of bone loss at both radius and tibia.
In conclusion, these findings indicate that lower fracture risk among postmenopausal Black women is not due to slower rates of bone deterioration and highlight the importance for postmenopausal women to avoid lower body weight and excessive weight loss to avert rapid bone loss and subsequent fractures.