Influence of body composition on bone mineral content in children and adolescents

Excess fat and fat-free mass have been extensively described in obese children, whereas few data about bone mineral content (BMC) variations are available in children. Dual-energy X-ray absorptiometry (DXA) allows a direct and accurate measurement of three body compartments (fat, lean, and BMC), subdivided into three regions (arms, trunk, and legs). The aim of our study was to evaluate the influence of body compartments on total BMC (TBMC) and regional BMC (RBMC) in obese and normal-weight subjects. Sixty-five obese and 50 normal-weight children and adolescents (age range: 5-18 y relative body weight: 160 ± 23% and 101 ± 12%, respectively), matched for sex and pubertal stage underwent a DXA total-body analysis. Obese subjects had significantly greater fat and lean compartments than normal-weight subjects (P <0.0001). TBMC was larger in obese children (1930 ± 670 g compared with 1480 ± 490 g, P <0.0001) as was RBMC (arms: 182 ± 81 g compared with 151 ± 65 g; trunk: 560 ± 223 g compared with 433 ± 169 g; legs: 788 ± 341 g compared with 539 ± 231 g, P <0.0001). We found lean mass to be the best correlate with TBMC (r = 0.91 in obese and 0.94 in normal-weight children). Multiple-regression analysis confirmed lean mass as one of the major determinants of TBMC and RBMC in children. However, differences in TBMC and RBMC were no longer present after correction for age, sex, and body- composition variables. There were no differences in TBMC and RBMC between obese and normal-weight children after correction for the confounding variables age and sex.