DETERMINANTS OF BONE MINERAL DENSITY IN PRE-ADOLESCENT FEMALES 397

Abstract

This study investigated the correlates and determinants of bone mineral density (BMD) in pre-adolescent (7-11 y) females. Subjects were participants in organized recreational, sub-elite and elite gymnastics programs, or were not involved in organized sport, BMD was measured by dual energy x-ray absorptiometry (DXA) for the total body (TB), femoral neck (FN) and lumbar spine (LS) in 72 girls and their biological mothers. Hours of gymnastics (GYM) training and general weight-bearing activity (GWBA) for the past year were determined by questionnaire, height (Ht) and weight (Wt) were measured by standard procedures, and body composition (percent body fat -% BF and lean body mass - LBM) was assessed by DXA. Dietary protein, calcium and vitamin D intakes were determined from a 3 day dietary record, and grip strength was measured with a Lafayette dynamometer. Significant positive correlations were obtained for TB BMD and subject age, Wt, Ht, LBM,% BF, and mother's BMD (0.33≤ r ≤ 0.66). LS BMD was significantly correlated with hours of GYM training (r=+0.32), whereas FN BMD was correlated with age, hours of GYM and general GWBA, left grip strength and mother's BMD (0.30 ≤ r ≤ 0.34). In forward stepwise multiple linear regression analysis, only LBM and mother's BMD entered as significant predictors of TB BMD (27% of explained variance). GWBPA was the only significant predictor of LS BMD (8% of explained variance), whereas GWBA, age and mother's BMD were significant predictors of FN BMD, accounting for 28% of the explained variance. Total weight-bearing activity was the most important determinant of FN and LS BMD, whereas body mass and maternal BMD, appear to be the most important predictors of TB BMD in pre-adolescent females.