Lean mass predicts the size-dependent and size-adjusted BMD better than fat mass in premenopausal females: a cross-sectional analysis

Introduction: In the human body, the influence of lean and fat masses on the bone tissue is unclear. This study was conducted to examine the association of different body compartments in order to find out the major determinant of bone mass. We used both size-dependent and size adjusted bone mass measures in the analysis

Methods:A group of 128 healthy premenopausal females, aged 25-50 years was selected randomly from the local community, stratified according to their BMI. Lean mass (LM), fat mass (FM), total body bone mineral density (TBBMD) and total body bone mineral content (TBBMC) were measured using a DXA scan. TBBMD was divided by the standing height to estimate height-adjusted total body BMD (TBBMD-ht). Furthermore, TBBMD was divided by the bone area and height to estimate bone mineral apparent density (BMAD).

Results:Both FM and LM showed significant and positive correlations with TBBMC and corresponding r values were 0.33 and 0.73, respectively (P <0.001 for both). LM (r = 0.43, P < 0.001), but not the FM (r = 0.16, P = 0.064) showed a significant correlation with TBBMD. When TBBMD was adjusted for height, the correlation with LM became less strong (r = 0.26, P0.004). When TBBMD was further adjusted to be representative of volumetric BMD (i.e. BMAD), the association with LM became negative (r = -0.31, p<0.001). In regression analysis a unit (1kg) change in LM was associated with a greater regression coefficient than a unit (1kg) change in FM for all size dependent and size-adjusted bone mass measurements.

Conclusions:Among these premenopausal women LM predicted bone mass stronger than FM. Magnitude and directions of the correlations between bone mass and LM were different when BMC was adjusted for bone size and height of subjects. These results support the idea that lean mass has dual effects on bone tissue where it influences both linear measurements and mineral content to different extents.

Journal of the Ceylon College of Physicians, 2014,45, 22-27