Bioactive Factors of Colostrum and Human Milk Exhibits a Day-Night Variation

The aim of this study was to determine the chronobiological variations of cytokines (IFN-γ, TGF-β) and hormones (melatonin and cortisol). The sample was collected from 42 mothers at three stages of maturity-day 3 (colostrum), day 10 (transitional milk) and day 30 (mature milk) postpartum, at two times of day: diurnal (12:00 h) and nocturnal (24:00 h), resulting a total of 252 samples. Melatonin concentration was increased in the nocturnal period from all milk maturation stages. This hormone concentration was lower in the mature milk. Cortisol concentration was higher in the mature milk during the diurnal period and it was lower in the nocturnal period when compared to colostrum and transitional milk. IFN-γ concentration did not vary between all periods. The transitional milk displayed higher concentrations of this cytokine in the nocturnal period whereas the concentration of IFN-γ decreased in the nocturnal period from the mature milk. When comparing the types of milk, it was observed lower concentrations of IFN-γ in mature milk in both periods. No significant variation in TGF-β concentration was detected between types of milk or at either time of day. These data support the hypothesis that there is a fluctuation in the production of hormone and cytokines and this leads to a need that adequate time of breastfeeding being crucial to ensure passive transfer of immunity, as well as for establishment of synchronization of newborn.