Lean Body Mass is a determinant of bone mineral measurements in American adolescents
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Background. Studies have demonstrated direct correlations between birthweight and body composition on adultonset osteoporosis. Objective. Determine the impact of birthweight and body composition in American adolescents on total bone mineral content excluding head (tBMC) and total bone mineral density excluding head (tBMD). Design/Methods. Cross-sectional study of individuals 13 to 15 years old who participated in the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2006. Primary outcome. Total body excluding head BMC (tBMC) and total body excluding head BMD (tBMD). Results. The cohort consisted of 1,295 males and 1051 females with an overall average age of 14 ± 0.8 years. tBMC, tBMD, and lean body mass index (LBMI) were greater in males than in females (tBMC: 1,330 ± 398 g vs. 1,115 ± 247 g, p<0.001; tBMD: 0.741± 0.13 g/cm2 vs. 0.686 ± 0.09 g/cm2, p<0.001; LBMI: 1.63 ± 0.27 g/cm2 vs. 1.47 ± 0.22 g/cm2, p<0.001). Fat mass index (FMI) was lower in males than in females (0.603 ± 0.36 g/cm2 vs. 0.812 ± 0.37 g/cm2, p<0.001). Significant correlations were seen between LBMI and tBMC (males: p<0.001, r2=0.51; females: p<0.001, r2=0.40) and tBMD (males: p<0.001, r2=0.42; females: p<0.001, r2=0.32). Weaker, statistically positive correlations were seen between birthweight and tBMC (males: p<0.002, r2=0.007; females: p<0.001, r2=0.028) and with tBMD (males: p<0.073, r2=0.003; females: p<0.01, r2=0.011). Birthweight, gender, age, ethnicity, phosphorus levels, FMI, and LBMI were the main determinants of tBMC (r2=0.61). This multivariate model was stronger than LBMI alone at predicting the variance of bone mineral measurements in adolescents. Conclusions. In our study, birthweight had a slight correlation with bone mineral measurements, but LBMI was a far greater determinant of tBMC and tBMD in adolescents.
KEY WORDS: osteoporosis; bone densitometry; body composition; birth weight; pediatrics.