Bone mineral density in 11-13-year-old boys: relative importance of the weight status and body composition factors

This study was aimed to investigate the influence of being overweight on bone mineral status in 11-13-year-old boys, who were divided into overweight (OW; n = 110) and normal weight (NW; n = 154) groups. Bone mineral density (BMD) at the whole body (WB), lumbar spine (LS) and femoral neck (FN), bone mineral content (BMC) at the WB, and body composition were assessed. Calculation of the bone mineral apparent density (BMAD) was completed for the WB, LS and FN. The BMC/height ratio was also computed. OW boys displayed similar values (P > 0.05) for LS and FN BMAD and lower (P < 0.05) WB BMAD, despite significantly higher values (P < 0.05) for more widely used WB and LS BMD, WB BMC and WB BMC/height in comparison with NW boys. Fat-free mass index (FFMI; kg/m(2)) had the highest correlation coefficients from the calculated body composition indices with all bone mineral values in NW boys. In OW boys, the FFMI had the highest correlation only with FN BMD, while other measured bone mineral values had highest correlations with either BMI or FMI indices. In conclusion, OW boys have higher crude WB BMD, BMC and BMC/height ratio in comparison with NW boys. However, the bone growth appears to be insufficient to compensate for the higher mechanical load applied on the bone by higher FM and also FFM values in OW boys. Excessive adiposity does not have a protective effect on the development of BMAD in growing boys reaching puberty.