This is how it works: One of the things for which the body uses L- tryptophan is to make serotonin; a brain chemical that scientific research has suggested may be a key link in the mechanism that triggers the onset of sleep. Serotonin is secreted by neurons to the reticular activating system, located deep in the brain. This system controls the level of activities of the whole central nervous system and is partly responsible for the mind’s ability to direct its attention. The lower portion of the reticular activating system is thought to maintain the brain’s normal state of wakefulness. And insomnia has been linked with damage to the neurons that normally secrete serotonin into the system.
When supply of serotonin is reduced due to the damaged neurons, its shortfall tends to keep one awake since the reticular activating system does not become dormant in absence of serotonin. In such circumstances, an extra supply of serotonin through milk may assist in getting a good night’s sleep.