In preterm babies, the biological clock is not yet fully developed. As a result, they are heavily dependent on their mothers – for example, through breastfeeding – to help regulate and train their biological clock. BioClock researcher Demy van Gilst had previously found that the nutrients in breast milk follow a daily rhythm. This new study shows that various hormones in breast milk also exhibit a clear day-night rhythm.
The researchers studied breast milk from mothers who had given birth before 30 weeks of pregnancy. They collected milk over several days and at different times of day. They then measured the concentrations of the hormones melatonin and cortisol in the samples.
Day-night rhythm in hormones
The results show that melatonin, the hormone that makes us sleepy, exhibited a clear day-night rhythm in the milk samples analysed. The highest concentrations were found at night. Cortisol also followed a day-night rhythm in most cases, peaking in the morning. These results are consistent with what we know about hormonal rhythms in full-term babies.
How can we use this knowledge?
These findings are relevant to the care of preterm babies. In the neonatal intensive care unit (NICU), babies are often given expressed breast milk that is administered hours later, or donor milk in which milk from different times of day has been mixed. As a result, natural time signals may be lost.
This new research reinforces the concept of chrononutrition: it is not only what a baby eats that matters, but also when. The study provides an important basis for future research into whether timing feeding to coincide with the time the milk was expressed can contribute to the development of the biological rhythm in preterm babies.
Read the full publication here.
