Nighttime breast milk contains higher levels of melatonin and somnogenic amino acids like tryptophan, potentially aiding infant sleep-wake cycle regulation.

“with the nighttime breast milk containing higher levels of melatonin and somnogenic amino acids like tryptophan breast milk nucleotides which are important structural components of dna and rna also show circadian rhythmicity some of the nucleotides peak during the day while others peak at night suggesting a potential role for these nucleotides as sleep inducers”