Contribution of Fat-Free Mass and Fat Mass to Bone Mineral Density Among Reproductive-Aged Women of White, Black, and Hispanic Race/Ethnicity

The objective of the study was to evaluate the contribution of fat-free mass (FFM) and fat mass (FM) to bone mineral density (BMD) and bone mineral apparent density (BMAD) among reproductive-aged women. Dual-energy X-ray absorptiometry scans were performed on 708 healthy black, white, and Hispanic women, 16-33 yr of age. The independent effect of FFM and FM on BMD and BMAD and the interaction of body composition measurements with race/ethnicity and age, were evaluated. FFM correlated more strongly than FM with BMD at the lumbar spine (r = 0.52 vs r = 0.39, p < 0.01) and the femoral neck (r = 0.54 vs r = 0.41, p < 0.01). There was a significant positive association between bone density measures [ln(BMD) and ln(BMAD)] and both ln(FFM) and ln(FM). The association of FFM with spinal BMD was stronger in 16-24-yr-old women than in 25-33-yr-old women (p < 0.006). The effect of FFM on femoral neck BMD was greater in blacks (p < 0.043) than Hispanics, whereas the effect of FM on spinal BMD was less (p < 0.047). Both FM and FFM are important contributors to bone density although the balance of importance is slightly different between BMD and BMAD.