Lean Mass As A Predictor Of Bone Mineral Density In Prepubertal Children

Abstract

The relative contribution of lean tissue and fat mass as predictors of bone mineral density (BMD) varies across the adult lifespan, especially during midlife and old age. The relative influences of fat and lean mass on BMD in prepubertal children remains inadequately characterized. Relations between body composition and bone status may be influenced by the obesity epidemic, low physical activity rates and suboptimal nutritional practices in children with the latter behaviors potentially impacting attainment of peak bone mass and subsequent risk for osteoporosis later in life. PURPOSE: To determine if fat or lean mass explains the greatest variance in BMD in prepubertal children, and if the contribution of the respective body composition components is impacted by sex. METHODS: Whole body (WB), lumbar spine (LS), femoral neck (FN) and hip (HIP) BMD, and total fat and lean mass were determined by dual energy X-ray absorptiometry (DXA) in 96 prepubertal children [9.2±1.3 y; males (n=49) and females (n=47)]. RESULTS: Mean WB BMD was 0.83±0.08 g/cm2 (WB Z-score=0.19). Fat (12.3±7.9 kg) and lean mass (28.9±6.7 kg) both correlated with WB BMD (r=0.45, r=0.77, respectively) and regional BMD (r range=0.36 to 0.67; all p<0.01). However, the relationships between fat and all BMD measures were eliminated after controlling for lean mass (all p>0.05). Alternatively, when accounting for the influence of fat mass, the relationship between lean mass and BMD persisted (r range=0.53 to 0.72, all p<0.01). Using linear regression, fat mass was not an independent predictor at any site whereas lean mass was an independent predictor of WB, LS, FN, and HIP BMD (all p<0.01), explaining 60%, 44%, 41% and 39% of the variance, respectively. Sex was also an independent predictor of LS BMD explaining 11% of the variance with females having greater LS BMD; however, sex was not a predictor at the WB or FN and HIP sites. CONCLUSIONS: Although fat and lean mass both influence BMD in prepubertal children, lean mass is the most significant independent predictor of BMD. These results encourage health behaviors that enhance lean mass, specifically physical activity, to optimize bone mineral accrual prior to adulthood. Supported by University of Illinois Research Board and NIH HD055352