Does body size account for gender differences in femur bone density and geometry?

The extent to which greater bone strength in men is caused by proportionate ly greater bone mass versus bigger bone size is not clear, primarily becaus e the larger overall body size of men has made direct comparisons of skelet al measures difficult, We examined gender differences in femur neck (FN) ar eal bone mineral density (BMD) values collected from 5623 non-Hispanic whit es aged 20+ years in the third National Health and Nutrition Examination Su rvey (NHANES III, 1988-1994) before and after correction for measured heigh t and weight, We supplemented the conventional areal BMD data (Hologic QDR 1000) with measurements of areal BMD and geometric properties (subperiostea l width, section modulus, and cortical thickness) made at narrow "cross-sec tional" regions traversing the FN and the proximal shaft using a structural analysis program, Before body size adjustment, men had significantly highe r values than women for all variables at the three measurement sites (p < 0 .0001), Adjustment for body size reduced the differences between the sexes for all variables but had a greater effect on BMD (1-8% higher in men) than on geometry (5-17% higher in men), When examined by age, the sex discrepan cy was significantly greater in the older group for all variables except su bperiosteal widths. We conclude that although body size difference may acco unt for most of the areal BMD difference between men and women, male bones are still bigger in ways that suggest greater bone strength. These differen ces may contribute importantly to lower fracture risk in men.