Melatonin is a hormone naturally produced by the body from serotonin (which is a neurotransmitter); it is known as the sleep hormone. It can also be obtained from certain foods such as walnuts. However, it also seems to have other functions and is known in particular as the hormone that regulates circadian rhythms, i.e. the wake-sleep cycle.
Although melatonin is synthesised by other organs (such as the retina and in bone marrow), its synthesis by the pineal gland in the brain is what allows it to regulate the body’s “biological clock” function. This synthesis process is photoperiod-dependent, as it is inhibited by light and thus takes place during the night. Its release into the bloodstream gradually increases with the decrease in brightness, to prepare the body for sleep. It peaks during the night and then decreases gradually to help the body wake up.
Melatonin supplementation can help resynchronise circadian day/night rhythms for people with sleep disturbances, in particular the elderly, in whom endogenous melatonin synthesis decreases as the pineal gland deteriorates. It also helps the body fall asleep faster and reduces the effects of jet lag.