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Abstract
The recent discovery of leptin, the product of the “ob” gene has greatly advanced the understanding of body adiposity and energy balance regulation. Serum leptin levels follow a circadian rhythm, which seems to be regulated predominantly by insulin increases levels and the circadian rhythm of cortisol. The aims of this study were to: (1) determine the effect of obesity on leptin 24 hours pattern; (2) determine the biological rhythm of leptin, insulin and cortisol. Thirteen subjects (10 women, three men) participated in this study. Serum samples were drawn at four hour intervals for a total of 24 hours. Leptin showed diurnal rhythmicity with peaks at 04.00 h (91.7±12.9 ng/ml) and troughs at 12.00 h (73.1±9.7 ng/ml). There was a strong association between leptin levels and BMI (r = 0.34; p < 0.001). The high levels of leptin may contribute to leptin resistance in obesity. Our data show the negative correlation over time between leptin and cortisol (r = −0.28, p = 0.005), and we demonstrate also that leptin and insulin are not correlated over time.