Melatonin, produced by the pineal gland, helps regulate the body’s sleep cycle. This hormone provides the brain with information about darkness and night, helping synchronize sleep timing with the roughly 24-hour circadian rhythm.
Light-sensitive cells in the retina send day-and-night information to the suprachiasmatic nucleus, the brain’s central circadian clock. In darkness, signals through the nervous system stimulate the pineal gland to release more melatonin; bright light suppresses its production. Melatonin usually rises in the evening and is much lower during daylight.
The pineal gland is a small, pine-cone-shaped endocrine gland located near the center of the brain. Melatonin does not act like an instant sedative or simply “switch off” consciousness. Its main role is to signal biological night and help time sleep and wakefulness.
Melatonin was isolated in 1958 by Aaron B. Lerner and colleagues while they were studying extracts from cow pineal glands and their effects on amphibian skin pigmentation. The same hormone is also involved in seasonal biological rhythms in many animals.