ABSTRACT
The purposes of this study were to examine the loss of bone mineral density (BMD) with increasing age and to investigate the relationship between the BMD and body composition. Cross-sectional measurements of total body and regional (head, arms, legs, trunk, ribs, pelvis and spine) BMD and body composition were made in 112 Japanese healthy women, aged 20 to 87 years, by dual-energy X-ray absorptiometry (DXA) . The mean peak BMD for the trunk, ribs, and pelvis was observed at the age of 40-49 years, in the arms and spine at the age of 30-39 years, and in the head, legs, and total body at the age of 20-29 years. The loss of spine BMD appears to begin prior to BMD loss in other regions and the rate of bone loss as a function of aging was readily apparent. Appendicular bone loss did not occur until age 49 yr, accelerated from ages 50 to 69 yr, and then decelerated somewhat after age 70 yr. In this cross-sectional analysis, we found cumulative loss of BMD from peak to 80-89 yr of age was 31.2% for the spine, 25.0% for the total body, and 21.5% for the ribs. To examine the relationship between the BMD and body composition, multiple regression analysis was performed with total body and regional BMD as the dependent variable and fat-free mass (FFM) and fat mass as the independent variable. From this analysis, the results indicated that FFM was a significant predictor of total body and regional BMD but did not evaluate the effects of exercise or other potential variables that might affect BMD. In conclusion, our findings indicate that spine bone loss begins prior to the loss of compact bone, and the rate of bone loss in the spine due to aging was greater than that of other specific regions. Secondly, FFM and fat mass are related to total and regional BMD in Japanese women with the strongest relationship being FFM.