Hip fracture arising from bone fragility contributes to both morbidity and mortality.(1,2) BMD assessment has long been the standard measure for identifying those at risk for osteoporotic fracture; however, this measurement provides, at best, an indirect indication of the strength of the bone.(3) Bone strength declines in old age, especially in women.(3) The aging effects on bone are characterized by decreasing BMD, mean cortical thickness, and section modulus, with accompanying increases in subperiosteal and endocortical widths.(4,5) Statistically, BMD is a good predictor of fracture; however, different geometrical configurations of bone may have the same BMD but not necessarily the same strength.(6,7) Studies are now identifying an association between hip geometry and fracture.(8,9) Therefore, to prevent the development of bone fragility, an understanding of the variables affecting all aspects of bone strength is important.
There is extensive research on the relationship between BMD and lifestyle variables. Studies have reported positive associations between BMD and the lifestyle variables, physical activity (PA) and dietary calcium intake (CI).(6,10–18) An interaction between PA and dietary calcium that affects BMD has also been reported,(12,15,18) and randomized controlled trials have shown that both of these lifestyle variables have a positive affect on BMD.(19–22)
Less is known about the relationship between lifestyle variables and the underlying geometry, an important element in the determination of bone strength and subsequent fracture risk.(23) Available data suggest that CI and PA may also have a favorable effect on the geometry of the femur.(3,6,17,24) Aspects of hip geometry associated with bone strength of the proximal femur can be estimated from data derived from DXA scans.(1,25–31) Section modulus, an index of bending resistance, has been shown to be more strongly associated with PA level than BMD.(6) Moreover, postmenopausal women with a daily CI in excess of 1200 mg have been shown to have greater femoral shaft section modulus and shaft subperiosteal width (SPW) compared with those with a daily intake of <800 mg.(17)
The purpose of this study was to determine the association between the modifiable lifestyle variables, habitual PA and dietary CI, and geometric indices of bone strength in the proximal femur in postmenopausal women.