Poster Presentation ANZOS-Breakthrough Discoveries Joint Annual Scientific Meeting 2018

Body mass is important to bone health, but so is its distribution: Associations between body composition and bone health measures in 11-12 year old children (#342)

Peter Simm 1 2 3 , Dorothea Dumuid 4 , Susan Clifford 1 3 , Grace Gell 1 3 , Timothy Olds 4 , Kate Lycett 1 3 , Melissa Wake 1 3
  1. Murdoch Children's Research Institute, PARKVILLE, VIC, Australia
  2. Department of Endocrinology, Royal Children’s Hospital , Melbourne, VIC, Australia
  3. Department of Pediatrics, University of Melbourne, Melbourne, Victoria, Australia
  4. Alliance for Research in Exercise, Nutrition and Activity (ARENA), University of South Australia, Adelaide, SA, Australia

Body composition may be an important driver of bone mass accrual in childhood. However, the relative impacts of the underlying components such as fat mass, fat-free mass, and/or truncal/non-truncal distribution remain unclear.

The Child Health CheckPoint is a cross-sectional study of 11-12 year olds, drawn from the Longitudinal Study of Australian Children. 1874 children completed multiple health measures. Body composition (truncal fat, non-truncal fat, fat free mass) was measured by bio-impedance. Bone health (trabecular/cortical density and geometry, polar stress-strain index (SSI)) was measured by peripheral quantitative computerised tomography (pQCT) of the non-dominant tibia.  Compositional multiple linear regression explored the relationship between body composition and bone health measures. Novel isocompartmental substitution modelling quantified the differences in bone health associated with the reallocation of mass between body compartments. Models were adjusted for age, height, pubertal stage, socioeconomic status and physical activity.

843 children (49.3% male) with complete data were analysed. Higher fat-free mass was associated with overall improved skeletal geometry and trabecular density, but lower cortical density. Associations with higher truncal and non-truncal fat were in the opposite direction. Bone strength (estimated by SSI) increased linearly with overall mass. Isocompartmental substitution modelling revealed profoundly opposing relationships with different elements of body composition. For example, a 6% absolute increase in fat-free mass was associated with a 1 standard deviation (SD) increase in SSI, while a 3% absolute reduction in truncal fat was associated with an approximately 1 SD increase. Associations for non-truncal fat were similar in pattern, but much weaker, to those for truncal fat.

While heavier children generally have stronger bones, it is higher lean mass combined with lower truncal fat that appears to drive improved outcomes at any given total body mass. Overweight interventions that maximise fat-free mass and minimise truncal fat may have additional benefits for long term skeletal health.