Optimizing Breast Milk Storage Timing to Support Babies' Circadian Development

Breast milk is widely recognized as the optimal nutrition source for infants, providing essential vitamins, minerals, and bioactive compounds that bolster the immune system and support healthy development. However, many mothers cannot breastfeed directly multiple times daily and instead rely on expressed milk stored for future feeding. Recent research highlights that the timing of milk storage and feeding may influence the baby's biological rhythms.

A study published in Frontiers in Nutrition explored how specific components of breast milk fluctuate over the course of a day and how these variations could impact infant health. The researchers from Rutgers University collected breast milk samples from 21 lactating women at four different times—6 am, 12 pm, 6 pm, and midnight—on two separate days. An additional group of 17 participants provided similar timed samples, totaling 236 samples analyzed for hormones including melatonin, cortisol, and oxytocin, as well as immune factors like immunoglobulin A (IgA) and lactoferrin.

Findings demonstrated that melatonin levels peaked around midnight, aligning with the hormone's role in regulating sleep-wake cycles, while cortisol was highest early in the morning, reflecting its involvement in alertness and metabolism. Other components, such as IgA and lactoferrin, remained relatively stable throughout the day but tended to be higher in milk from mothers with very young infants, possibly aiding immune defense and gut microbiome development.

These fluctuations suggest that expressing and feeding breast milk at specific times might help reinforce the infant's developing circadian rhythm, which is crucial during early life when the internal biological clock is still maturing. Dr. Melissa Woortman emphasized that these hormonal patterns follow maternal circadian rhythms and are transferred via milk. Meanwhile, Prof. Maria Gloria Dominguez-Bello noted that labeling milk as 'morning,' 'afternoon,' or 'evening' and matching feeding times accordingly could better preserve natural bioactive and hormonal profiles.

Despite certain limitations—such as demographic factors and individual differences—the research underscores the potential importance of timing in breast milk storage and feeding. Implementing time-based labeling could be a simple yet effective way to optimize the health benefits of expressed milk, supporting sleep, metabolism, and immune development in infants, especially in modern societies where constant maternal presence is less feasible.

As the infant's circadian system matures, the hormonal composition of breast milk adapts, reflecting the dynamic interplay between maternal and infant biological rhythms. Future studies are needed to examine how infants respond to these variations, but current evidence suggests that strategic timing of milk expression and feeding could enhance early developmental outcomes.