No relationship between leptin and cortisol in obese children and adolescents

Recent findings have shown that leptin downregulates the steroid producing system in the adrenal. We studied the interactions of leptin, insulin and cortisol in obese children and adolescents at different stages of maturation. In 44 boys (age 11+/-3.1 yr, body mass index BMI] 29+/-5.3 mean +/- SD]) and 35 girls (age 11.4+/-2.6 yr, BMI 29+/-4.3), blood levels of leptin, insulin, cortisol, and glucose were determined. Fat mass (FM) was calculated by bioelectrical impedance. No significant differences were found between boys and girls with respect to humoral and anthropometric characteristics. When children were divided according to maturation stage (prepubertal, pubertal, and late/postpubertal) insulin was higher in the more mature groups (p<0.01) and leptin was higher in the pubertal group (p=0.03). In the prepubertal and pubertal groups, the expected positive relationship between adiposity and leptin was found although the magnitude of this association decreased with maturity. In none of the groups studied was cortisol significantly correlated to leptin. Insulin (p=0.03) and glucose (p=0.01) were positively associated with cortisol in the prepubertal group after adjustment for adiposity. However, in the pubertal group an inverse correlation was found between insulin and cortisol (p=0.03), and between insulin and glucose after control for adiposity. In the late/ postpubertal group, no significant correlations were found between estimates of adiposity and humoral parameters even after adjustment for gender. Stepwise multiple regression failed to detect a significant influence of cortisol to explain the variation in leptin, and vice versa. BMI contributed to the variation in leptin (adj. R2 =0.275, p<0.0001), and glucose added 5% to the variation in cortisol (p=0.03). The results do not confirm the inverse association between leptin and cortisol found in adults. Although BMI reflects levels of leptin, it is likely that several other factors in conjunction with fatness modulate the relationship with leptin. Whether leptin per se exerts an influence on the hypothalamic-adrenal-adipo axis remains to be investigated in longitudinal studies.