Background: Sex differences in body composition exist before puberty, but the reason for this phenomenon is unknown. The physical changes that occur during puberty are mediated, in part, through sex steroids, insulin-like growth factor I (IGF-I), and leptin. However, data are lacking that address the extent to which concentrations of these hormones influence body composition, bone mass, and density in prepubertal children.
Objective: We investigated the effects of IGF-I, dehydroepiandrosterone sulfate, and sex steroids on body composition and fat distribution and the effects of these hormones and leptin on total body bone mineral content (TBMC) and volumetric bone mineral density (vBMD) at the femoral neck and lumbar spine (LS) in 255 healthy children (137 girls), aged 7-8 y.
Design: Body composition, fat distribution, TBMC, and vBMD were derived by using dual-energy X-ray absorptiometry. Association between variables was examined by using regression analysis.
Results: No sex differences were found in age, height, or weight. However, girls had significantly more total body fat, trunk fat, and higher LS vBMD but significantly less fat-free soft tissue, TBMC, and femoral neck vBMD than did boys. Girls also had significantly (P < 0.001) higher IGF-I, estradiol, testosterone, and leptin concentrations than did boys. Estradiol concentrations predicted percentage body fat, which supported an effect of estrogen on fat storage. Leptin had an independent effect on LS vBMD, which suggests a positive effect for leptin on trabecular bone.
Conclusions: The hormones examined explained 3-17% of the variations in body-composition measures, fat distribution, and bone density, which suggests that other factors are important predictors of prepubertal sexual dimorphism.