Bone Abstracts

Objectives: To investigate whether bone health outcomes (volumetric bone mineral density, geometry and strength) is associated with adiposity and muscle in late childhood.

Methods: Design: Population-based cross-sectional study nested within the Longitudinal Study of Australian Children. Participants: 11–12 year-olds attending the Child Health CheckPoint physical module. Exposures: Measures of adiposity (BMI z-score, fat mass (kg), waist circumference (z-score)) and muscle (lean mass (kg), skeletal muscle mass (kg), lower leg muscle cross-sectional area (CSA)). Outcomes: Measures of bone health assessed via peripheral quantitative computed tomography, yielding tibial bone density (trabecular and cortical), geometry (endosteal and periosteal circumference) and strength (polar stress–strain index (SSI)). Statistical analysis: Multivariable linear regression models adjusted for age, sex, height, puberty, neighbourhood disadvantage and moderate to vigorous physical activity. In addition, models of adiposity were further adjusted for skeletal muscle mass and models of muscle were further adjusted for fat mass. Interaction tests also assessed the effect of sex. We present the fully adjusted models below.

Results: Of the 3,764 eligible children, 1,220 (32%) had bone and body composition data available. On average, children were aged 11.4 years (S.D.: 0.4), half were male, and one quarter were overweight or obese. Bone health outcomes showed differential associations with adiposity and muscle for females and males. In females, better bone health was most strongly associated with higher BMI z-scores and higher waist circumference. For example, each unit higher in BMI z-score was associated with better bone geometry (endosteal and periosteal circumference) and strength (SSI), with effect sizes ranging from 0.17–0.31 (all P<0.001). Whereas in males, better bone health was most strongly associated with skeletal muscle mass and lower leg muscle CSA, with effect sizes ranging 0.13–0.34 (all P<0.001). Across both sexes fat mass showed little association with the bone measures.

Conclusions: By late childhood, adiposity and muscle show differential associations with bone health for male and females, consistent with previous reports of gender dimorphism for bone health outcomes. These findings point to the complexity of looking at each exposure measure separately and highlight the need to consider body composition as a whole (i.e. composition analyses).

Conflict of Interest: All authors declare no conflict of interest.

Funding: The Child Health CheckPoint has been supported to date by the Australian National Health and Medical Research Council (NHMRC) (1041352, 1109355), The Royal Children’s Hospital Foundation (2014-241), Murdoch Childrens Research Institute and The University of Melbourne. Research at the Murdoch Childrens Research Institute is supported by the Victorian Government’s Operational Infrastructure Support Program.

Disclosure: The authors declared no competing interests.