The Effect of Body Composition Variables on Bone Mineral Density in young prepubertal females

Abstract

A growing body of evidence in the field of nutrition suggests that diet and exercise/physical activity (PA) is beneficial to bone health. The relationship of body composition variables to bone mineral density (BMD) in adult females indicate that a higher lean body mass (LBM) and larger body mass index (BMI) to be significant factors in preventing osteoporosis. However, the relationship between BMD and LBM and BMI has not been investigated in young females. The purpose of this investigation is to examine the effect PA, LBM and BMI have on BMD of young females who are overweight. BMD and LBM were evaluated by dual-energy X-ray absorptiometry. To further quantify LBM, isometric grip strength (GS) was assessed in the dominant forearm by dynamometry. We examined 54 white females between the ages of 7-11 (x=9.5+0.2; Tanner stage x=1.6±0.1) who were divided into 2 groups by physical activity pattern (GRP 1 x=2.3 d/wk±0.08, n=38; GRP 2 x=3.3 d/wk±0.08, n=16). Body weight (GRP 1 x=61.6±2.6, GRP 2 x=60.8±2.7), height (GRP 1 x=1.46±0.0, GRP 2 x=1.44±0.0), BMI (GRP 1 x=28.6±0.8, GRP 2 x=28.1±0.8) and percent body fat (GRP 1 x=38.8±1.2, GRP 2 x=38.9±1.4) were not significantly different between the groups. BMD values in the two groups were compared by ANCOVA with GS as a covariant. There was no significant difference in the BMD values which was dependent on GRP (F=0.379, df=l,42, p=0.542). However, there was a significant relationship between the covariant GS and BMD when controlling for GRP (F=43.417, df=1,42, p=0.005). A multiple regression using variables PA, GS, LBM and BMI was applied to predict BMD with significant results (R=.831, F=22.24, df=4, 40, p=0.0005). However in the overall equation only BMI (p=0.039), LBM (p=0.055) and GS (p=0.023) contributed significantly to the prediction equation. We conclude that in prepubertal females a greater body mass as well as more muscle mass is significant to the development of bone health.