Body composition changes with age have gender-specific impacts on bone mineral density.

Body weight, smoking, alcohol, physical activity, and diet have been proven to affect bone mineral density (BMD) directly or indirectly. Of these, body weight is perhaps best known to affect BMD. However, there is some debate as to whether lean body mass (LBM) or fat mass (FM), the two components of body weight, most determines BMD. Recently, newer peripheral densitometry devices have been developed, which have the advantages of low cost and portability, and this has made field epidemiologic study of osteoporosis possible. As the number of studies that have focused on the contribution made by body composition to BMD is limited, we investigated the relative contribution of LBM and FM to BMD in healthy Korean subjects. 402 age- and weight-matched subjects over 45 years old were selected from a population-based cohort. The mean ages of men and women were 64.1 +/- 8.7 (mean +/- SD) and 64.2 +/- 12.7 years, and mean weights were 63.0 +/- 8.2 and 63.1 +/- 8.2 kg, respectively. BMD was measured by peripheral dual-energy X-ray absorptiometry (DEXA) and body composition by bioelectrical impedance. Sociodemographic characteristics and physical activities were investigated using a standard questionnaire delivered by face-to-face interview. BMDs were 0.48 +/- 0.01 and 0.37 +/- 0.11 g/cm2 in men and women, respectively. In men, age, weight, body mass index (BMI), LBM, FM, physical activity, smoking, alcohol, and education were significantly correlated with BMD. In women, age, weight, BMI, LBM, FM, education, years since menopause, number of deliveries, and number of children breast-fed were significantly correlated with BMD. By multiple regression, LBM, education, smoking, and alcohol in men, and age, LBM, FM, smoking, and number of delivery in women were independent determinants of BMD. LBM was an important contributor for BMD in men, but both LBM and FM were equally important contributors in female to BMD. This stems from the fact that body composition changes with age differ in men and women. Thus, the augmentation of muscle mass in men and the maintenance of an optimal weight in women act to prevent osteoporosis.