| Summary: | Introduction: Overweight children have greater bone mass than their healthy weight peers; however, they sustain more fractures. Thus, there is a need to better understand the relation between body fat and bone strength and aspects of bone quality such as bone microstructure that contribute to bone strength.
Methods: I aimed to determine the cross-sectional relationship between fat mass (FM) and aspects of bone quality (strength, geometry, density and microstructure) at the distal radius and distal tibia in boys (n = 137, 15.6 ± 3.3 yrs on average) and girls (n = 157, 14.5 ± 3.9 yrs) in the context of the functional model of bone development (after adjusting for lean mass (LM)). FM and LM were measured using dual energy X-ray absorptiometry and bone quality was measured using high resolution-peripheral quantitative computed tomography.
Results: In boys, FM negatively predicted bone strength at the radius but not at the tibia. Conversely, FM did not significantly predict bone strength in girls. In both boys and girls, FM negatively predicted total area at the radius but not the tibia. In girls but not boys, FM positively predicted cortical bone mineral density at the tibia but not the radius. For bone microstructure, FM did not significantly predict many variables; however, FM negatively predicted cortical thickness at the tibia in boys, trabecular thickness at the tibia in girls, and cortical porosity at both the radius and tibia in girls. In nearly all cases, LM mediated the relationship between FM and bone quality, whereby prior to adding LM to regression models FM positively predicted bone quality; however, after adjusting for LM the positive associations became non-significant or negative.
Conclusions: The relation between fat and bone is complex and appears to be sex- and site-specific. My results also highlight the important influence of lean mass on bone strength. Longitudinal studies with larger cohorts and more overweight and obese participants would clarify the sex-specific muscle-fat-bone relationships during growth and into adulthood. The potentially hazardous influence of high levels of fat mass on child and youth bone health must be considered among the adverse consequences of overweight and obesity. === Medicine, Faculty of === Medicine, Department of === Experimental Medicine, Division of === Graduate
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