Melatonin Concentrations and Antioxidative Capacity of Human Breast Milk According to Gestational Age and the Time of Day

Background: While changes in the composition of breast milk throughout the lactation period are well known, little is known about the antioxidative capacity of breast milk and its regulation as a function of time of day.

Objective: The aim of this study was to evaluate the antioxidative capacity in breast milk and its regulation by time of day.

Methods: Melatonin, superoxide dismutase (SOD), glutathione peroxidase 3 (Gpx3) concentrations, and the total antioxidative capacity (TAOC) were analyzed in 105 breast milk samples and 12 maternal serum samples from 21 healthy nursing mothers.

Results: Comparison between daytime breast milk (collected from 1000-2200 h) and nighttime breast milk (collected from 2200-1000 h) revealed significantly higher concentrations of melatonin and Gpx3 in nighttime milk (melatonin: 1.5 pg/mL [1.0-2.1] day vs 7.3 pg/mL [3.8-13.6] night, median [quartiles], with an estimated mean night-to-day ratio of 5.2 [3.9, 7.1], P < .001; Gpx3: 1436 ng/mL [765-2060] day vs 1800 ng/mL [1242-2297] night, night-to-day difference 192.1 [0.6, 383.7], P = .049). Subgroup analysis showed that melatonin had a circadian rhythm in both preterm and term milk, with a significantly higher nighttime concentration ( P < .001), while antioxidant enzymes had a circadian rhythm only in preterm milk, with a significantly higher nighttime concentration for Gpx3 and a significant higher daytime concentration for SOD and TAOC ( P = .041 and P = .049, respectively). We found no significant correlation between the concentration of melatonin and the concentration of SOD, Gpx3, or TAOC. Moreover, there were no significant correlations observed between gestational age and the concentration of melatonin and antioxidant enzymes.

Conclusion: Because of its higher melatonin and Gpx3 content, future research is needed to determine if preterm nighttime milk ought to be the first choice in the feeding of high-risk preterm infants.