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The Relationship Between Leptin, Metabolic Hormones, Exercise and Body Composition in Adolescents

During adolescence, little is known about the relationship between leptin and metabolic hormones and how these are modified by body composition and exercise. This study determined: 1) the relationships between leptin, triiodothyronine, cortisol, and insulin, and 2) whether these relationships were modified by body composition and exercise. Fasting hormonal concentrations were assessed from 80 girls and 80 boys, aged 11-18 yr. In a multiple regression model, including the hormones and gender, only gender and insulin were significant predictors of leptin (R2 = 0.394; p <0.001). In a second model, including body fat and exercise, the levels of body fat, gender, free triidothyronine and cortisol explained 59.6% of the variance in leptin (p <0.05). The results suggest that in adolescents, the relationship between leptin and insulin is mediated by body fat. Leptin is negatively associated with cortisol in boys and with thyroid hormones in girls; these hormones possibly interact to sustain normal growth and maturation.