Leptin May Play a Role in Bone Microstructural Alterations in Obese Children

Context: Bone mass is low and fracture risk is higher in obese children. Hormonal changes in relation to skeletal microstructure and biomechanics have not been studied in obese children. Objective: The objective of the study was to ascertain the relationships of obesity-related changes in hormones with skeletal microstructure and biomechanics. Design: High resolution peripheral quantitative computed tomography (HR-pQCT) was used to compare three-dimensional cortical and trabecular microstructure and biomechanics at load-bearing and nonload bearing sites in obese and lean children. The relationship between leptin, adiponectin, testosterone, estrogen, osteocalcin and sclerostin and skeletal microstructure was also determined. Setting: The study was conducted at a tertiary pediatric endocrine unit in the United Kingdom. Participants: Obese and lean children were matched by gender and pubertal stage. Results: Radial cortical porosity (mean difference -0.01 [95% CI: -0.02, -0.004], P = .003) and cortical pore diameter (meandifference -0.005 mm [95% CI: -0.009, -0.001], P = .011) were lower in obese children. Tibial trabecular thickness was lower (mean difference -0.009 mm [95% CI: -0.014, -0.004], P = .003), and trabecular number was higher (mean difference 0.23 mm(-1) [95% CI: 0.08, 0.38], P = .004) in obese children. At the radius, fat mass percentage negatively correlated with cortical porosity (r = -0.57, P < .001) and pore diameter (r = -0.38, P = .02) and negatively correlated with trabecular thickness (r = -0.62, P < .001) and trabecular von Mises stress (r = -0.39, P = .019) at the tibia. No difference was observed in the other biomechanical parameters of the radius and tibia. Leptin was higher in obese children (805.3 +/- 440.6 pg/ml vs 98.1 +/- 75.4 pg/ml, P < .001) and was inversely related to radial cortical porosity (r = 0.60, 95% CI: [-0.80, -0.30], P < .001), radial cortical pore diameter (r = 0.51, 95% CI [-0.75, -0.16], P = .002), tibial trabecular thickness (r = 0.55,95% CI: [-0.78, -0.21], P = .001) and tibial trabecular von Mises stress (r = -0.39, 95% CI: -0.65, 0.04, P = .02). Conclusion: Childhood obesity alters radial and tibial microstructure. Leptin may direct these changes. Despite this, the biomechanical properties of the radius and tibia do not adapt sufficiently in obese children to withstand the increased loading potential from a fall. This may explain the higher incidence of fracture in obese children.