Is the Dose-Response Relationship Between Body Mass and Hip Bone Mineral Density in Women Influenced by Diet, Physical Activity, or Menopause?

Purpose. Investigate the relationship between body mass and hip bone mineral density (BMD) and the extent to which this association is influenced by potential mediating factors. Design. Cross-sectional. Setting. Approximately 20 cities in Utah and Wyoming. Subjects. Subjects were 262 apparently healthy, nonsmoking females. Measures. Hip BMD was assessed using dual energy X-ray absorptiometry. Physical activity (PA) was measured objectively using accelerometers. Calcium and vitamin D were measured using the Block food frequency questionnaire. Menopause status and bone drug use were measured using a questionnaire. Analysis. General linear models and partial correlations. Results. With body mass divided into three categories, hip BMD differed significantly across the groups in a dose-response manner: low mass (mean +/- standard deviation [SD]), .876 +/- .085 g/cm(2); moderate, .932 +/- .109 g/cm(2); and high mass, .995 +/- .112 g/cm(2) (F= 21.5, p < .0001). The relationship between mass and hip BMD was not affected by differences in age, height, menopause status, calcium or vitamin D intake, PA, or use of bone prescription drugs. Conclusion. These findings suggest that women with low body mass tend to have low hip BMD and those with high mass tend to have high BMD. Controlling for the potential mediating variables did not influence the dose-response relationship between mass and BMD. It appears that lifestyle may not influence the body mass and BMD relationship, making it a challenge for women with low mass to avoid risk of low RAM.