Lean Soft Tissue Mass is a Stronger Predictor of Bone Mineral Density than Fat Mass

Abstract

Whether lean soft tissue mass or fat mass is the major independent contributor to bone mineral density in postmenopausal women, especially when controlling for physical activity remains incompletely characterized. PURPOSE: To examine: 1) the associations between historical and recent physical activity and bone mineral density and 2) the relative strength of associations among lean soft tissue mass, fat mass and bone mineral density, controlling for historical and recent physical activity in postmenopausal women. METHODS: Using a cross-sectional design, middle-aged postmenopausal women (n = 67, mean age 58.1±3.8) were assessed for historical and recent physical activity and completed dual energy x-ray absorptiometry (DXA) scanning. Subjective physical activity was measured via the Bone Loading History Questionnaire, Bone-specific Physical Activity Questionnaire, and Global Physical Activity Questionnaire. Objective physical activity was measured via accelerometer (steps/day). Bone status (whole body and femoral neck) and body composition (lean soft tissue mass and fat mass) were assessed using DXA. RESULTS: No significant relationships were found between historical physical activity and current bone mineral density. Recent physical activity, as assessed using the Bone Loading History Questionnaire, was negatively associated with whole body and femoral neck bone mineral density (r range = -0.29 to -0.37; p<0.05). Whole body bone mineral density was negatively related to steps/day (r = -0.28; p<0.05). Regardless of the physical activity measure included in the regression analysis (i.e. steps/day or Bone Loading History Questionnaire), hormone replacement therapy and lean soft tissue mass were the only significant independent predictors (all p<0.05) of whole body and femoral neck bone mineral density. CONCLUSIONS: Lean soft tissue mass, not fat mass or recent physical activity, is a significant independent contributor to bone status at the whole body and femoral neck sites reinforcing the importance of lean mass maintenance in middle-aged postmenopausal women.