The findings suggest that giving babies milk expressed at the same time of day it was pumped may strengthen circadian signals, supporting sleep-wake patterns and overall health on Newborns.
New Jersey: The timing of feeding expressed breast milk could play an important role in infants’ health and sleep development, according to new research.
Breast milk is a dynamic food, shaped by a mother’s nutrition, fitness, genetics—and even her body’s internal clock. Researchers at Rutgers University and the University of Puerto Rico found that certain bioactive components in milk fluctuate throughout the day in line with maternal circadian rhythms.
For example, melatonin, the hormone that regulates sleep, peaked in breast milk around midnight, while cortisol, which helps manage stress, was highest early in the morning. Meanwhile, levels of oxytocin (the “love hormone”), the milk protein lactoferrin, and the antibody immunoglobulin A remained relatively stable across the day.
“We all have circadian rhythms in our blood, and in lactating mothers, these are often reflected in breast milk,” explained Dr. Melissa Woortman of Rutgers University. “Hormones like melatonin and cortisol follow these rhythms and enter milk from maternal circulation.”
The findings suggest that giving babies milk expressed at the same time of day it was pumped may strengthen circadian signals, supporting sleep-wake patterns and overall health—especially in newborns who are still establishing a biological rhythm.
The study recruited 21 mothers from Robert Wood Johnson Medical Center in New Brunswick, New Jersey, all over the age of 21 and recently postpartum. They provided 10-milliliter breast milk samples at 6 a.m., noon, 6 p.m., and midnight across two separate days, about a month apart. Additional samples from 17 more mothers brought the total to 236 samples analyzed.
Professor Maria Gloria Dominguez-Bello, also from Rutgers, suggested a simple but practical solution: labeling stored milk by time of day—such as “morning,” “afternoon,” or “night”—and feeding it accordingly.
“Aligning expressed milk with the time it is fed could help preserve the natural hormonal and microbial composition of breast milk, while giving infants important circadian cues,” Dominguez-Bello said.
For busy mothers who rely on pumping, this approach could be a valuable way to maximize the benefits of breast milk and support healthier infant development.
