No Relationship Between Youth‘s Physical Activity And Changes In Insulin, Leptin, Cortisol And Growth Hormone

Abstract

PURPOSE: The interrelationships among changes in habitual physical activity (PA) and changes in insulin, leptin, cortisol and growth hormone (GH) are complex, particularly in youth, and studies have not considered the influence of change in weight status on these relationships. This investigation determined the association between changes in these hormones and PA over two years in youth who were normal weight and became overweight, were overweight and normalized their weight, or simply maintained their weight status. METHODS: Data were collected from 120 youth at baseline (mean age 9.8 years) and two years later. Participants were selected from a larger cohort to represent the following: normal weight (>5th and <85th BMI percentile) or overweight (≥ 85th BMI percentile) at both time points, normal weight that became overweight and overweight that became normal weight. Fasting, morning plasma leptin, cortisol, GH and insulin were measured via radioimmunoassay. Habitual physical activity (PA) was assessed via questionnaire. Partial correlations and multiple regression analyses were used to determine the relationship between changes in insulin and changes in leptin, cortisol, GH, PA and BMI percentile, while controlling for race and sex. Additionally, correlations were computed between change in PA and changes in leptin, cortisol and GH. RESULTS: Change in insulin was related to change in BMI percentile (r=0.25, p<0.05) and change in leptin (r=0.29, p<0.05), but was not related to changes in cortisol (r=-0.08) or GH (r=0.16) (p>0.05). Likewise, change in PA over the two year period was not related to changes in any of the hormones (p>0.05). Multiple regression analyses revealed that change in leptin accounted for 9% of the variance in insulin change, while change in BMI percentile accounted for 4% of the variance (p<0.05); no other variables were significant. CONCLUSIONS: In this sample of youth, changes in or maintenance of weight status over a two year period appears to only impact the association between hormonal changes in insulin and leptin. Thus, weight status has a stronger association with the insulin-leptin relationship than does habitual physical activity. Supported by NINR #NR01-1837.