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This study sought to determine the chronobiological variations in soluble and cellular components of human breast milk. The material was collected from 36 mothers at three stages of maturity - 3 days (colostrum), 10 days (transitional milk) and 30 days (mature milk) postpartum - and at two times of day - diurnal (12:00 h) and nocturnal (24: 00 h) - making a total of 216 samples. Fat and calorie content, antibody concentration, C3 and C4 proteins of the complement system, superoxide anion release by milk mononuclear (MN) and polymorphonuclear (PMN) phagocytes, and concentration of the superoxide dismutase enzyme (CuZn-SOD) were determined. No difference in fat concentration was found between milk collected at the different times or between milk maturation stages but in the transitional milk the calorie concentration was higher in the nocturnal period. IgA was higher in milk collected in the diurnal period regardless of milk maturation. IgG and IgM were at higher concentrations in the diurnal period for both transitional and mature milk. The C3 protein increased significantly in the diurnal period regardless of milk maturation, and the C4 protein increased significantly during the diurnal period in the colostrum and transitional milk stages. Mature milk MN phagocytes had the highest superoxide during the diurnal period. Superoxide release by PMN phagocytes was higher in colostrum and mature milk collected in the diurnal period. CuZn-SOD increased significantly in diurnal and nocturnal colostrum. This chronobiological variation during the first month postpartum may represent an additional breastfeeding mechanism to improve adaptation to environmental changes and establish biological rhythms in the temporal synchronization process.
França et al. (Tue,) studied this question.