Endocrine Abstracts

Context: The increase in bone mineral content (BMC) and density (BMD) measured by dual-energy X-ray absorptiometry (DXA) in obese children may not sustain the mechanical load associated with weight, and the factors influencing bone mineralization are not well known.

Objective: We described bone mineralization in overweight- obese (ow/ob) and lean (non-ow/non-ob) boys in relation to body composition.

Methods: Cross-sectional study in the Pediatric Endocrinology Unit of Angers University Hospital. Two-hundred-forty-nine ow/ob boys aged 8-18 underwent DXA and insulin, testosterone, and IGF-1 measurements. Bone mineralization was compared with data obtained from 301 lean boys of similar age and height from the NHANES study from 2011 to 2015, using the same DXA model. Path analyses were performed to evaluate the factors associated with total body less head (TBLH) BMC.

Results: The mean age and height-adjusted difference in TBLH-BMC between obese and lean boys was 241±20 g/cm². Each 1 kg/m² increase in BMI was associated with +39±6 g of TBLH-BMC in lean subjects vs. +25±3 g in obese subjects (P<0.05). Each 1 kg/m² increase in lean BMI (LBMI) was associated with +78±5 g of TBLH-BMC in lean and obese boys, and each 1 kg/m² increase in fat mass index (FMI) was associated with a decrease of 9±3 g of TBLH-BMC. These findings suggest that the rise in TBLH-BMC observed in obese boys cannot sustain the increased mechanical load associated with weight. The Path analyses for TBLH-BMC Z-score in lean boys shows that TBLH-BMC Z-score was directly influenced by LBMI and height Z-scores (positively) and indirectly influenced by testosterone, FMI, and height Z-scores (positively, mediated through LBMI Z-score). And the path analyses for TBLH-BMC Z-score in obese boys shows that TBLH-BMC Z-score was directly influenced by LBMI and height Z-scores (positively) and indirectly influenced by insulin, height Z-scores (positively, mediated through LBMI Z-score), indirectly influenced by IGF-1, testosterone, and insulin Z-scores (positively, mediated through height and LBMI Z- scores). Finally, FMI Z-score indirectly influenced TBLH-BMC Z-score both positively (through LBMI Z-score) and negatively (through its negative impact on IGF-1 and testosterone Z-scores).

Conclusion: Bone mineralization in obese children and adolescents, although increased in response to the increased mechanical load of weight, did not follow the same positive relationship with BMI as that observed in lean boys. Lean body mass, had a similar positive relationship with bone mineralization in obese and lean boys, whereas fat mass had a negative impact.