The pineal gland in the brain secretes the hormone melatonin in response to the light-dark cycle. Melatonin regulates body temperature, the sleep cycle, hormone activity and other circadian functions run by the body's internal biological clock. At night, higher levels of melatonin are released to induce sleepiness; levels drop during early morning hours and throughout the day to promote alertness. Disruptions in this normal secretion pattern have been linked to various types of sleep disturbances.

Yet some studies have observed that nightly melatonin supplementation in children with autism and other neurological and developmental disorders appears to improve sleep patterns in up to 80% of these children.