Because milk contains L tryptophan, a biochemical substance that can make people feel tired and sleepy, and a small amount of morphine, these substances have certain sedative and hypnotic effects, especially L tryptophan, which is the main raw material for the brain to synthesize hydroxyl color. Serotonin plays a key role in brain sleep, which can temporarily inhibit brain thinking activities, thus making people want to sleep without any side effects. Moreover, milk can be absorbed on the stomach wall, and calcium in milk can also remove tension, so it is beneficial to the elderly.