The idea of warm milk as a sleep aid seems to come from the idea that an amino acid called tryptophan-which is found in milk (and turkey)-is thought to play a role in making people sleepy by increasing the amount of serotonin in the brain (serotonin has sedative qualities).
However, there is no scientific proof that there is enough tryptophan in a glass of milk to actually induce a sedative effect in your brain. In fact, some sources reveal that you’d have to drink as much as a half gallon of milk to ingest enough tryptophan to make a difference.
So does a glass of warm milk really help you fall asleep? If you believe it does, then it probably will help. The benefits seem to be more psychological than scientific.