Doyle M. Cummings, Pharm.D.,FCP, FCCP Department of Family Medicine & Pediatrics Brody School of Medicine at East Carolina University 600 Moye Blvd Greenville, NC 27834 cummingsd@ecu.edu Gender Differences in Fitness vs. Fatness as Predictors of Insulin Resistance in Adolescents: Results from NHANES 1999-2002 Authors: Doyle M. Cummings Pharm.D., Katrina D. DuBose, Ph.D., Satomi Imai, Ph.D., David Collier, MD, Ph.D. INTRODUCTION METHODS RESULTS The prevalence of childhood obesity continues to increase and appears to be associated with an increased risk of diabetes mellitus in late adolescence or adulthood. Insulin resistance in adult females is associated with body composition while in males it is also associated with fitness. This relationship during childhood is not well understood. The purpose of this study is to assess the relationship between insulin resistance (HOMA), waist circumference (abdominal obesity), and VO2 max (fitness) among adolescents. Design: NHANES (National Health and Nutrition Examination Survey, 1999-2002) – nationally representative cross-sectional sample Subjects: Adolescents ages 12-18yr; fasting subsample; n = 1,078 Measures: HOMA: Estimate of Insulin Resistance; calculated as follows: [fasting plasma insulin (mU/L)] x [fasting plasma glucose (mg/dl)] /405; log transformed to normalize distribution Waist circumference in cm measured by protocol Estimated VO2max [ml / (kg x min)] from submaximal treadmill test Age (yrs), race (white vs. non-white), sex (M or F) BMI (kg/m2) Statistical Analysis utilized SUDAAN with appropriate NHANES weights to account for complex sampling design: Descriptive statistics for demographic characteristics Pearson correlation coefficients for bivariate analysis of continuous variables Linear Regression Model with lnHOMA as outcome variable compared to waist circumference and VO2max while controlling for BMI, age, and race. Table 1: Subject Characteristics Linear Regression via SUDAAN BOYS (r2 = 0.37) GIRLS (r2 = 0.31) Both VO2max (β = -0.008, Only waist circumference p<0.01) and waist circumference (β = 0.02, p<0.001) and not (β = 0.02, p<0.001) were VO2max was an independent independent predictors of predictor of lnHOMA while lnHOMA while controlling for controlling for age and race. age and race. When examined by BMI category (normal weight vs. >85th %tile), for boys, the same pattern of association of both waist circumference (all boys) and VO2max (in >85th %tile boys) was demonstrated, while, for girls, only waist circumference and not VO2max was associated with lnHOMA in both BMI groups. Parameter All n = 1,078 Mean ± SEM Boys n = 573 Girls n = 505 Age (yr) 15.03 ± 0.08 15.14 ± 0.07 14.92 ± 0.13 HOMA 2.87 ± 0.07 2.83 ± 0.11 2.92 ± 0.11 Waist Circumference (cm) 78.99 ± 0.68 79.99 ± 0.79 77.95 ± 0.91 BMI (kg/m2) 22.65 ± 0.24 22.72 ± 0.30 22.58 ± 0.33 VO2max (ml/kg/min) 43.57 ± 0.52 47.4 ± 0.64 39.59 ± 0.44 Significant Bivariate Pearson Correlations lnHOMA was highly correlated with BMI in both genders PCC = 0.56 in all, 0.57 in males, 0.56 in females lnHOMA was highly correlated with waist circumference in both genders PCC = 0.56 in all, 0.59 in males, 0.54 in females lnHOMA was significantly and inversely correlated with VO2max in males but not in females PCC = -0.20 in all, -0.29 in males, -0.06 in females CONCLUSIONS Among adolescents, important gender differences appear to exist in the relationship between insulin resistance and cardiorespiratory fitness. While waist circumference and BMI are important predictors in all children, fitness appears more important in boys than girls. Longitudinal studies are needed to determine if low cardiorespiratory fitness and associated insulin resistance, as shown here, are predictive of higher risks for developing type 2 diabetes. If so, early determination of cardiorespiratory fitness could help guide not only who is in most need of intervention, but also the nature of the interventions offered. ACKNOWLEDGEMENTS Supported in part by a grant from the Health Resources and Services Administration (D54HP03396).