Melatonin (suppression)

Melatonin is the most important hormone of the pineal gland and can be described as the body’s signal for the nightly dark phase. It promotes sleep in humans and activity in nocturnal animals. Melatonin is produced and stored continuously in the pineal gland from serotonin, and is released only in the dark. Light causes secretion of melatonin to be suppressed. If no melatonin is released the level of melatonin in the bloodstream falls as a result of decomposition processes. As melatonin is the most important measurable marker for the circadian phase of the internal clock the melatonin-suppressing effect is generally equivalent to the circadian effect, i.e. the biological effect of light on the internal clock.