Milk contains two hypnotic substances that people didn't know in the past, one of which is tryptophan synthesized by serotonin, which can promote sleep. Because of its function, people often only need a glass of milk to fall asleep. The other is natural morphine, which has similar anesthetic and sedative effects. Therefore, if you drink milk in the morning, it will inevitably inhibit people's cerebral cortex and affect work and study during the day. In addition, drinking milk in the morning is not conducive to digestion and absorption. This is because protein in milk can only be absorbed by human body after it is decomposed into amino acids in stomach and small intestine. In the morning, on an empty stomach, the stomach empties quickly, so the milk is discharged into the large intestine and has not been digested. Therefore, nutrition experts believe that it is best to drink milk at night or half an hour before going to bed. Drinking milk before going to bed helps you sleep.