Impact of lean mass and fat mass on bone mineral density: The Hordaland Health Study

Abstract Objectives To examine the relationship between soft tissue composition and bone mineral density (BMD) of the hip and whether these relationships differ by gender and age. Methods Femoral neck BMD and total body soft tissue composition were measured by dual X-ray absorptiometry in a population-based sample of 5205 men and women 47–50 and 71–75 years old. Analysis of covariance was used to explore possible modifying effects of sex and gender on the impact of fat and lean mass on BMD. Results The difference in BMD per kilo lean mass (LM) was larger than the difference per kilo fat mass (FM). The effect of FM on BMD was significantly greater among women than among men. In multivariate adjusted analyses, 10 kg increase in LM was associated with a 0.083 (95% confidence interval [CI]: 0.075, 0.092) g/cm2 increase in BMD. A 10 kg increase in FM was associated with 0.013 (0.007, 0.019) g/cm2 increase in BMD among men and 0.021 (0.017, 0.026) g/cm2 among women. There was indication of a steeper dose–response relationship at lower levels of FM among women. Conclusions Compared to FM, LM was generally more strongly related to BMD of the femoral neck in middle-aged and elderly men and women. FM was a significantly stronger predictor of BMD among women than among men, particularly at lower levels of FM.