Bone density, microarchitecture and strength estimates in white versus African American youth with obesity

Background: African Americans (AA) have more favorable bone density and microarchitecture compared to Whites (W), which may explain their observed lower fracture rates. Obesity has deleterious effects on bone microarchitecture and strength estimates and is associated with an increase in fracture risk. Adolescence and young adulthood are periods of active bone accrual and also periods characterized by an increasing prevalence of obesity. The effect of obesity on the relationship between race and bone parameters remains unclear, particularly in youth. Objective: To assess differences in BMD, bone microarchitecture and strength estimates in AA and W adolescents and young adults with moderate to severe obesity. We hypothesized that racial differences in bone endpoints in lean youth would also be noted in youth with moderate to severe obesity. Methods: We evaluated 24 AA and 48 W adolescent and young adults with a mean age of 18.2 +/- 2.4 years and a median body mass index (BMI) of 44.8 (40.5-49.4) kg/m(2) who underwent dual energy X-ray absorptiometry (DXA), high resolution peripheral quantitative computed tomography (HRpQCT), extended cortical analysis (ECA) and micro-finite element analysis (FEA) to obtain measures of volumetric bone mineral density (vBMD), bone geometry, microarchitecture, and strength estimates at the distal radius and tibia. Results: We found no differences between AA and W for total fat and lean mass, and areal BMD Z-scores (p > 0.05 for all). At the distal radius, no significant differences were detected in vBMD, bone geometry or microarchitecture (p > 0.05 for all); however, stiffness and failure load were higher in the AA group (p = 0.031 and 0.047 respectively). At the distal tibia, cortical vBMD was higher in AA vs. W (p = 0.012), while trabecular number was higher and trabecular separation lower in W vs. AA (p <= 0.028). Stiffness and failure load trended higher in AA vs. W (p = 0.052 and p = 0.048, respectively). Groups did not differ for any other bone parameter (p > 0.05). Conclusion: Racial differences in bone endpoints appear to be less marked in those with moderate to severe obesity, suggesting that effects of obesity may blunt the effect of race on bone endpoints.