New research from the University of Extremadura in Badajoz, Spain, has shown that the composition of breastmilk changes over the course of the day to help babies sleep at night. Naturally occurring chemicals called nucleotides, which have previously been linked to sleepiness, were found to be at their highest levels at night-time.

Researchers tested the breastmilk of 30 mothers who had been breast-feeding for at least three months. Samples of milk were collected before each feed over a 24-hour period, with between six and eight samples collected per mother.

The scientists also noted that this may have an impact on when mothers express their breastmilk and feed it to their baby, as milk expressed in the morning may not help a baby to sleep as well as milk expressed in the evening.