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Objective:
Age-related bone loss is a challenging problem associated with an increased risk for fragility fractures and serious morbidity. Declining bone mass occurs in conjunction with changes in soft tissue, affecting total and regional adiposity and muscle mass. Age-related changes in soft tissue are diverse; these include an increase in fat mass (FM), which is redistributed in the trunk, and a decrease in lean mass (LM), mostly in the limbs. Regardless of the tissue assessed however, early identification of alterations in body composition may have substantial clinical impact because changes characterizing osteoporosis, sarcopenia, and obesity may determine other age-related conditions, or become treatable comorbidities of chronic disease. Thus, in the context of age-related bone and soft tissue changes, implementation of strategies aimed at development of targeted, individualized interventions through exercise, optimization of nutrition or other lifestyle factors is important. Analogous to an effective estimate of bone mass, DXA allows for reliable assessment of soft tissue providing accurate measurements of region-specific and whole-body composition. We hypothesized that DXA measures of body composition at central and peripheral regions are associated with distinct age-specific changes in active, aging women. Our aim was to determine the site-specific differences in body composition for the trunk and the appendicular skeleton stratified by age, and to establish DXA-based reference values for bone, muscle, and fat mass in central and peripheral body regions, in healthy White women living in the Mediterranean area. Finally, we aimed at defining different patterns of age-related, regional changes in body composition, with reference to the age of peak and overall reduction of values.

Materials and Methods:
Body composition of the trunk and detailed analysis of its anatomical components, namely, the ribs, the thoracic spine, the lumbar spine and the pelvis as well as peripheral sites, including the arms, legs, and the limbs was measured, and fat mass (FM) and lean mass (LM) ratios were calculated in 330 women aged 20-85 years, using DXA. Statistical analysis of the data was then performed.

Results:
Bone mass diminishes at all sites in older women, with an overall reduction for the trunk at 20.7% and peripheral at 22.3%, although degenerative changes result in a spurious increase of bone status in the lumbar spine (<em>p</em> < 0.001). We found that the distribution of fat in aging women is mostly peripheral (17 - 18.7%), and then after menopause, fat accumulates in the trunk (19.5 - 21.2%), similar to the male pattern of adiposity. Unlike fat, muscle mass is located centrally in the trunk during a woman's lifespan, and significant decreases in both the LM (<em>p</em> < 0.001) and FM (p<0.01) are seen preferentially in the legs of aging women.

Conclusion:
Distinct changes in body composition, in terms of quantity of the major tissue elements (bone, fat, muscle) and distribution in the various anatomic sites that ensue with aging that may serve as predictors of quality and quantity of life.