Are Physical Activity Associations with Bone Mineral Density Modified by Metabolic Traits?

We assessed the relationship of physical activity with BMD at various sites (by DEXA), and examined potential modifying factors, including insulin sensitivity by euglycemic clamp in 765 healthy subjects. Responses from physical activity questionnaires were used to determine total physical activity (PA), moderate physical activity (mod-PA), and sedentary time. Neither activity nor sedentary time correlated with rib, L-spine, or T-spine BMD in univariate analysis (Table). Significant univariate variables were included in multivariate analyses. In multivariate analyses of arm BMD, only female sex (β=-0.74, P<0.0001) and adiponectin (β=-0.08, P=0.016) were significant. Multivariate analyses of pelvis BMD found independent associations with BMI (β=0.35, P<0.0001), female sex (β=-0.18, P=0.0003), PA (β=0.10, P=0.04), and mod-PA (β=0.12, P=0.024). Age (β=-0.11, P=0.003), female sex (β=-0.67, P<0.0001), BMI (β=0.25, P<0.0001), and mod-PA (β=0.11, P=0.005) were independently associated with leg BMD. These results suggest that BMD increases with the physical activity in the arms, legs, and pelvis and is inversely related to sedentary time in the pelvis and legs, and these associations may be modified by age, sex, BMI, and adiponectin, depending on the site, with physical activity being more important to pelvis and leg BMD than arm BMD. Sedentary time, CRP, PAI-1 and insulin sensitivity play a minor role in BMD.