Cortisol, leptin and free leptin index (FLI) in newborns in the first days of life and their importance for body weight programming

BACKGROUND: Birth weight and leptin seem to be the factors responsible for early programming of body weight in later life. A marker for leptin action is free leptin index (FLI), which depends on soluble leptin receptor (Ob-Re) (FLI = leptin/Ob-Re). In the present article, we suggest that FLI is modulated partly by cortisol variations observed in newborns in the first days of life and is connected with their postnatal weight loss. METHODS: The study group consisted of 44 full-term newborns. Leptin, cortisol and Ob-Re concentrations were determined in the umbilical cord blood (UCB) and in the newborns’ blood (NB) on the fourth day of life, free leptin index (FLI = leptin/Ob-Re) was calculated. Correlations between the assessed parameters and the somatic features of the newborns were examined. RESULTS: Birth weight, length and chest circumference of newborns were positively correlated with leptin concentration in the UCB but not with FLI in the UCB. Cortisol and leptin concentrations, as well as FLI values declined concomitantly with body weight, and were lower on the fourth day of life than on the first one; however, Ob-Re concentration increased (p < 0.0001). There was a positive correlation between the newborns’ birth weight loss percentage evaluated on the fourth day of life and FLI in newborns (R = 0.39; p < 0.01). Positive correlations between cortisol and Ob-Re in UCB (R = 0.35; p < 0.02) and in NB (R = 0.36; p < 0.01), as well as a negative correlation between cortisol and FLI (R = -0.32; p < 0.03) in NB were noted. CONCLUSIONS: Our data suggest a possible relationship between cortisol and a soluble leptin receptor (Ob-Re), which changes free leptin index (FLI) and is connected with birth weight loss in newborns. Whether these observations are important for programming of future body weight of children requires further research.