Fat-free body mass is the most important body composition determinant of 10-yr longitudinal development of lumbar bone in adult men and women.

The purpose of this study was to analyze the longitudinal relationship between body composition and lumbar bone mineral density (LBMD) and lumbar bone mineral content (LBMC) in (young) adults over a 10-yr period. The data are from the Amsterdam Growth and Health Longitudinal Study. Two hundred twenty-five men and 241 women were measured at 27, 32, and/or 36 yr of age. Nine body composition components were explored: total body weight, standing height, body mass index, waist circumference, hip circumference, waist to hip ratio, sum of four skinfolds, fat mass, and fat-free mass (FFM). Stratified analyses were performed by gender and adjustment was made for physical activity and calcium intake. Univariate multilevel analyses indicated that FFM was significantly positively related to the 10-yr development of both LBMD and LBMC in both sexes. Total body weight, standing height, and body mass index also showed a significant positive univariate relationships with LBMD and LBMC in both sexes, fat mass only with female LBMD. All best predictive multiple regression models included FFM, explaining 4-27% of the variation in bone mineral over this 10-yr period. Because FFM can be interpreted as a proxy for skeletal muscle mass, these results indicate the importance of muscle contractions on bone to increase bone strength in (young) adults.