LEAN TISSUE MASS IS A BETTER PREDICTOR OF BONE-MINERAL CONTENT AND DENSITY THAN BODY-WEIGHT IN PREPUBERTAL GIRLS

Purpose and Methods. Body weight is the most extensively studied corre late of bone mass and is widely used as a covariate in statistical eva luations of bone mineral parameters. Lean tissue mass (LTM) also corre lates with bone mass. We evaluated the correlations linking each of th ese two parameters with bone mineral content and bone mineral density in 41 prepubertal girls, including ten swimmers, 18 gymnasts and 13 no nathletes. Lean tissue mass, bone mineral content and bone mineral den sity were measured using dual-energy X-ray adsorptiometry (Hologic QDR -1000/W; Hologic Inc., Waltham, MA, USA). Forward stepwise multiple re gression was used to evaluate correlations linking bone mineral conten t or density (the dependent variables) to body weight or lean tissue m ass (the independent variables). Results. Body weight and lean tissue mass showed strong correlations with all bone mineral content and dens ity measurements in the simple linear regression analysis, with lean t issue mass yielding the highest Pearson's correlation coefficients. In the multiple regression model, lean tissue mass consistently explaine d the largest proportion of the variance, whereas body weight had litt le influence or was eliminated from the model. The slopes of the regre ssion lines of bone mineral content or density on body weight were sig nificantly steeper in the subgroup of gymnasts (P<0.001), whereas the slopes of the regression lines of bone mineral content or density on l ean tissue mass were significantly less steep in the swimmers (P<0.05) . Conclusion. Our data indicate that lean tissue mass is a significant predictor of bone mass in prepubertal girls and explains a larger par t of the variance of bone mineral content and density than body weight . Use of body weight as a covariate in studies of bone mineral density may lead to erroneous results in prepubertal girls.