Geometric indices of bone strength are associated with physical activity and dietary calcium intake in healthy older women

A population-based study on 1008 postmenopausal women identified that the 24% of women achieving high levels of PA and CI had 3.4–4.4% higher femoral bone strength in axial compression and 1.7–5.2% in bending than those achieving low levels, indicating that lifestyle factors influence bone strength in the proximal femur. Introduction: Extensive research has shown that increased physical activity (PA) and calcium intake (CI) decrease the rate of bone loss; however, there is little research on how these lifestyle variables affect bone geometry. This study was designed to investigate the effects of modifiable lifestyle variables, habitual PA and dietary CI, on femoral geometry in older women. Materials and Methods: Femoral geometry, habitual PA, and dietary CI were measured in a population-based sample of 1008 women (median age ± interquartile range, 75 ± 4years) enrolled in a randomized controlled trial (RCT) of calcium supplementation. Baseline PA and CI were assessed by validated questionnaires, and 1-year DXA scans (Hologic 4500A) were analyzed using the hip structural analysis technique. Section modulus (Z), an index of bending strength, cross-sectional area (CSA), an index of axial compression strength, subperiosteal width (SPW), and centroid position, the position of the center of mass, were measured at the femoral neck (NN), intertrochanter (IT), and femoral shaft (FS) sites. These data were divided into tertiles of PA and CI, and the results were compared using analysis of covariance (ANCOVA), with corrections for age, height, weight, and treatment (calcium/placebo). Results and Conclusions: PA showed a significant dose–response effect on CSA all hip sites (p < 0.03) and Z at the narrow neck and intertrochanter sites (p < 0.02). For CI, there was a dose–response effect for centroid position at the intertrochanter (p = 0.03). These effects were additive, such that the women (n = 240) with PA in excess of 65.5 kcal/day and CI in excess of 1039 mg/day had signifi