Associations of fat and muscle masses with bone mineral in elderly men and women

Associations of fat and muscle masses with bone mineral status were studied in 301 men and women aged greater than or equal to 65 y. Bone mineral and soft tissue composition were estimated by using dual-energy X-ray absorptiometry. Univariate correlations suggested that muscle is associated more closely than fat with bone mineral content (BMC) as well as with bone mineral density (BMD) in men. In women, however, correlations of BMC with muscle were only slightly greater than those with fat and correlations with BMD were consistently, greater with fat than with muscle. This suggests that correlations of BMC with muscle are influenced by bone and body size, especially in women. A multiple-regression model was developed that adjusts BMC for bone area, knee height, age, and the independent effects of fat and muscle. In men, muscle remained more closely associated with adjusted BMC than with fat. In women, fat mass was associated significantly with BMC but muscle mass was not. The exception was for women taking estrogen, in whom neither fat nor muscle was associated significantly with adjusted BMC. This study suggests that body fatness may be more important than muscle in maintaining bone mineral in elderly women not taking estrogen.