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

Abstract 

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, 16–33yr 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.

Key Words: Body composition, Bone mineral density, Fat-free mass, Fat mass