Breast milk is often called a baby’s first superfood, and new research shows it may also deliver important time-of-day signals that help infants develop healthy sleep and activity patterns.
A study from Rutgers University, published in Frontiers in Nutrition, found that breast milk changes over the course of the day. Levels of melatonin, the hormone that promotes sleep, were highest at night, while cortisol, which helps with alertness, peaked in the morning. Other immune-boosting proteins like immunoglobulin A and lactoferrin were most abundant in the first month after birth, likely giving newborns extra protection as their immune systems develop.
“We noted differences in the concentrations of bioactive components in breast milk based on time of day, reinforcing that breast milk is a dynamic food,” said lead author Melissa Woortman, PhD, who completed the work at Rutgers’ Department of Nutritional Sciences.
That means babies who receive expressed milk may miss out on natural circadian cues if the timing is mismatched. The researchers suggest a simple step: label pumped milk as “morning,” “afternoon” or “night” and try to feed it to babies at the corresponding time.
“The timing of these cues would be particularly critical in early life, when the infant’s internal circadian clock is still maturing,” said senior author Maria Gloria Dominguez-Bello, PhD, a professor of biochemistry and microbiology at Rutgers.
The study was small, 38 mothers provided 236 samples, and more research is needed to confirm how infants respond to these hormonal fluctuations. Still, the idea fits with growing evidence that nutrition and circadian rhythms are closely linked, even from the earliest days of life.
“In modern societies where it may not be feasible for mothers to stay with their infants throughout the day, aligning feeding times with the time of milk expression is a simple, practical step that maximizes the benefits of breast milk when feeding expressed milk,” Woortman said.
This research was supported by a CIFAR fellowship to Maria Gloria Dominguez-Bello and the Ferring Pharmaceutical COVID-19 Investigational Grant in Reproductive Medicine and Maternal Health to Laura K.