Leptin serum levels in normal weight and obese children and adolescents: relationship with age, sex, pubertal development, body mass index and insulin.

OBJECTIVE: Leptin, the product of the ob gene, is present in higher concentrations in blood of obese subjects than of lean subjects. There is scarce information on the role of leptin in the pathogenesis of human obesity and little is known about leptin serum levels in obese children. DESIGN, SUBJECTS AND MEASUREMENTS: To evaluate the influences of age, sex, pubertal development and weight excess on serum leptin levels, we have studied 390 obese subjects (OS) and 320 normal weight subjects (NWS) aged 5-16 y. Fasting insulin concentrations were assayed in NWS, and an oral glucose tolerance test was carried out in OS and total insulin area under the curve (TIA) was calculated.
RESULTS: Log-transformed values of leptin serum concentrations appeared to be distributed according to an acceptable Gaussian pattern. As observed in adults, serum leptin concentrations in children and adolescents were also increased (4-5 times) in OS as compared to NWS. In both males and females, subdivided according to pubertal stages, serum leptin varied significantly in stage IV-V as compared to the lower stages, with a reduction in males and an increase in females. On comparing the two sexes, greater serum leptin concentrations were observed in females of both NWS and OS. A significant linear correlation was found in both groups, subdivided according to sex and pubertal stage, between log values of serum leptin and standard deviation scores (SDS) of body mass index (BMI), and log-transformed relative body weight (RBW). Using partial correlation analysis in subjects subdivided according to sex and pubertal stages, log values of serum leptin and fasting insulin values, adjusted by age and SDS of BMI, correlated significantly with a weaker correlation in males than in females. In OS, the leptin concentrations correlated better with TIA than with fasting insulin. A weight reduction program (WRP) was carried out in 141 OS and significant reductions of serum leptin and fasting insulin were observed, showing a reduction of RBW. There was a correlation between the reduction of RBW and of serum leptin, but not of fasting insulin. No variation was found in non-responsive OS. RBW reduction correlated with leptin, but not with insulin (fasting and TIA), evaluated before the therapeutic program started.
CONCLUSION: As observed in adults, obese children and adolescents have higher serum leptin concentrations. However, several conditions should be taken into account when evaluating leptin concentrations in children. There are differences, independent of BMI, relative to pubertal stage and sex, females having greater leptin concentrations than males. There is evidence of a possible role for leptin in the effectiveness of a weight reduction program in OS.