Racial differences in lumbar marrow adipose tissue and volumetric bone mineral density in adolescents and young adults with obesity

BACKGROUND: Areal bone mineral density (BMD) of the lumbar spine by DXA is greater in Black compared to White adolescents. Bone strength is determined not only by BMD but also its microenvironment, and marrow adipose tissue (MAT) has been shown to be an important determinant of skeletal integrity, independent of BMD. Racial differences in volumetric BMD (vBMD) and MAT in adolescents and young adults with obesity are unknown. OBJECTIVE: To assess racial differences in lumbar vBMD and MAT in Black and White adolescents and young adults with obesity and to assess body composition determinants of bone parameters. We hypothesized that Blacks will have higher vBMD and lower MAT of the lumbar spine compared to Whites. METHODS: The study group comprised 77 adolescents/young adults, 25 Black and 52 White, (mean age 18.2 ± 2.5 years, range 13 to 24 years) with moderate to severe obesity (mean body mass index (BMI) 46.2 ± 7.3 kg/m(2), range 35.5 to 69.7 kg/m(2)). Groups were similar in age, BMI, and sex distribution (p > 0.84). Subjects underwent QCT of the lumbar spine (L1−L2) for assessment of vBMD with the use of a calibration phantom and 1H-MRS/MRI for quantification of lumbar MAT content (L1-L2) and abdominal fat and thigh muscle mass. Groups were compared by Student's t-test or Wilcoxon test. Correlation analysis was performed to assess associations between bone parameters and body composition. RESULTS: Black adolescents/young adults with obesity had higher vBMD compared to Whites (p < 0.0001), while there was no significant difference in lumbar MAT (p = 0.64). There were also no significant differences in body composition measures between groups (p ≥ 0.28). An inverse association between MAT and vBMD was observed in Whites (r = −0.47, P = 0.001) but not in Blacks (p = 0.6). There were no significant associations between body composition measures and bone parameters (p > 0.1). CONCLUSION: There are racial differences in lumbar vBMD in adolescents and young adults with moderate to severe obesity, with Blacks having higher vBMD than Whites, while there were no differences in MAT content. The known inverse association between BMD and MAT was only observed in Whites but not in Blacks, suggesting possible racial differences in stem cell differentiation into the bone and fat lineages.