Lean soft tissue contributes more to bone health than fat mass independent of physical activity in women across the lifespan

Objectives: To investigate the association between lean soft tissue (LST) and fat mass (FM) on bone health variables in women across the lifespan, while taking into account the influence of objectively measured habitual physical activity (PA). Study design: A total of 104 women, 37 young (23.3 ± 2.6 years), 28 middle-age (49.2 ± 5.4 years), and 39 old (68.3 ± 6.4 years) participated in this cross-sectional study. All underwent a DXA scan and wore a pedometer for 7 days. Main outcome measures: Bone mineral content (BMC) and BMD of the whole body (WB), lumbar spine (LS) and proximal femur (PF), and body composition (FM and LST) were assessed with DXA and PA (steps/day) was assessed from 7 day pedometer counts. Results: LST was significantly and positively associated with PF and LS BMD (r = 0.34; 0.67, p < 0.05), and WB, PF and LS BMC (r range = 0.41-0.59, p < 0.05) in all age groups and WB BMD in the middle-age group (r = 0.72, p < 0.05) independent of PA, FM, and hormonal status. FM was not positively associated with any bone variable in any age group when adjusted for PA, LST, and hormonal status. PA was significantly associated with WB BMD in the middle-age group (r = 0.60, p < 0.05), independent of LST, FM, and hormonal status. Conclusions: LST contributes more to bone health in women across the lifespan than FM, independent of PA and hormonal status.