Age-related changes in body composition and their relationship with bone mineral density decreasing rates in central south Chinese postmenopausal women.

The purpose of this work is to investigate the age-related changes in body composition and their relationship with bone mineral density decreasing rates (BDR) in central south Chinese postmenopausal women. BDR is the percentage of bone mineral density (BMD) decreasing value relative to the peak bone mass. A cross-sectional study was conducted on 779 healthy postmenopausal women, aged 50-77. Lumbar spine, total hip, and femoral neck BMD and body composition were measured by dual-energy X-ray absorptiometry. In women under 65, lean mass levels showed a stable downward trend, and were significantly higher than those of the 65-70 and >70 age groups; however, the fat mass levels showed no significant difference between the age groups. After controlling for age, age at menopause, and height, both fat mass and lean mass positively correlated with BDR at the lumbar1-4 spine, the femoral neck and the total hip. When BDR at the lumbar1-4 spine was used as the dependent variable, a higher R (2) change and partial R (2) were seen in fat mass than the age, age at menopause or lean mass, indicating that fat mass was the most significant determinant of BDR at this site. When BDR at the femoral neck or total hip was used as the dependent variable, respectively, lean mass was a more significant determinant than that of fat mass. We found that with advancing age, lean mass begins to decrease in women aged over 65 years, but fat mass levels show no significant difference between the age groups. Both fat mass and lean mass positively correlate with BDR, with site-specific differences. Fat mass is the most significant determinant of BDR at the lumbar spine, whereas lean mass is the most significant determinant of BDR at the femoral neck and total hip.