Age and sex effects on the association between body composition and bone mineral density in healthy Chinese men and women.

OBJECTIVE: Many studies have examined the relationships between body composition and bone mineral density (BMD), but little attention has been given to how these relationships vary by age and sex. The aim of this study was to investigate the distributions of lean mass (LM), fat mass (FM), and BMD and the correlation between body composition and BMD in Chinese men and women of different ages.

METHODS: In total, the body compositions of 1,475 men and 1,534 women aged 20 to 96 years were analyzed. Using dual-energy x-ray absorptiometry, we measured the BMD of the spine, femur, and total body and the LM, FM, and percentage of body fat (Fat %). The population was divided into groups based on age and sex: young, premenopausal, and postmenopausal women and young, middle-aged, and older men. The correlations between BMD and variables of body composition were investigated using the Pearson correlation test and multiple regression analysis.

RESULTS: The peak BMD values of the spine, femur, and total body are observed in women aged 30 to 39, 20 to 29, and 30 to 39 years, respectively, and in men aged 20 to 29 years at all sites. The peak LM, FM, and Fat % values were observed at age 40 to 49, 60 to 69, and 70 to 79 years in women, respectively, and at 40 to 49, 70 to 79, and 70 to 79 years in men, respectively. A statistically significant correlation was observed between LM and BMD of all sites (r = 0.253-0.591, P < 0.01) in all groups. However, FM was significantly correlated to BMD only in postmenopausal women and older men (r = 0.089-0.336, P < 0.01). Fat % negatively correlated to BMD in young people (r = -0.169 to -0.366, P < 0.05). When stepwise regression models were analyzed, LM remained the strongest predictor of total body, spine, and femur BMD (standardized coefficients = 0.264-0.637, P < 0.001) in Chinese men and women of different ages.

CONCLUSIONS: We believe that LM is the strongest predictor of BMD at all ages for Chinese men and women, even though positive correlations between FM and BMD existed in old people.