The composition of breast milk changes throughout the day and it is a “mistake” for the mother to express the milk and store it for feeding the baby later, says a new study.

The baby should be given milk at the time of day that it issues from the mother’s breast. Breast milk contains various ingredients, such as nucleotides, which perform a very important role in helping babies sleep, it says.

“It is a mistake for the mother to express the milk at a certain time and then store it and feed it to the baby at a different time,” says Cristina L. Shez, lead study author and researcher at the Chrononutrition Lab, University of Extremadura, Spain.

“You wouldn’t give anyone a coffee at night, and the same is true of milk. It has day-specific ingredients that stimulate activity in the infant, and other night-time components that help the baby to rest,” explains Sanchez.

Scientists looked for three nucleotides in breast milk (adenosine, guanosine and uridine), which excite or relax the central nervous system, promoting restfulness and sleep, and observed how these varied throughout a 24-hour period, says an Extremadura University release.

The milk, collected from 30 women living in Extremadura, was expressed over a 24-hour period, with six to eight daily samples. The highest nucleotide concentrations were found in the night-time samples (8 p.m. to 8 a.m.).

The World Health Organisation (WHO) says breast milk is the best food for the newborn, and should not be substituted, since it meets all the child’s physiological requirements during the first six months of life.