Diurnal Rhythms in Melatonin and Cortisol in Very Preterm Human Milk

Why It Matters

Time‑specific hormonal signals in expressed milk could aid circadian development in vulnerable preterm infants, prompting reconsideration of current feeding practices. Aligning milk delivery with maternal hormone rhythms may improve sleep, metabolism, and neurodevelopment outcomes.

Key Takeaways

• Melatonin showed diurnal rhythm in all 25 preterm milk series
• Cortisol rhythmic in 18 of 25 preterm milk series
• Melatonin peaks around 4 AM; cortisol peaks near 8:30 AM
• Female infants' mothers had earlier cortisol peaks than males
• Findings support exploring time‑matched milk feeding in NICUs

Pulse Analysis

The discovery that very preterm human milk retains robust melatonin and cortisol rhythms reshapes our understanding of neonatal nutrition. Chrononutrition, the study of how meal timing interacts with biological clocks, has gained traction in adult health research, yet its application in the NICU remains nascent. By confirming that maternal hormonal cues survive even the stress of extreme preterm birth, the study provides a biological foundation for re‑engineering feeding protocols that honor the time‑of‑day of milk expression. This could help bridge the gap between the infant’s immature endogenous clock and the external environment, potentially mitigating the developmental delays associated with circadian misalignment.

Current NICU practices often pool donor milk or store expressed milk for extended periods, effectively erasing the natural hormonal fluctuations that signal day and night. The loss of these cues may contribute to the high incidence of sleep disturbances, metabolic dysregulation, and neurodevelopmental challenges observed in preterm populations. Integrating time‑matched feeding—delivering milk when its melatonin or cortisol levels are at physiological peaks—offers a low‑cost, non‑pharmacologic intervention that aligns with the body’s innate timing mechanisms. Early pilot programs could track infant sleep patterns, cortisol awakening responses, and growth metrics to assess efficacy.

Future research must move beyond observational hormone profiling to randomized trials that test the clinical impact of chronologically aligned milk delivery. Key variables include maternal chronotype, light exposure, and stress levels, all of which influence hormone secretion. Moreover, standardizing collection timestamps and developing bedside labeling systems will be essential for operationalizing this approach. If successful, time‑specific milk feeding could become a cornerstone of precision neonatology, improving outcomes for the most vulnerable newborns.