Melatonin, which is also known as the “mother hormone of chronobiology,“ is a hormone that is primarily produced in the pineal gland. It is present in humans, animals, plants and even in single-celled and phylogenetically ancient algae that’s three billion years old. Melatonin regulates the biological clock of humans as a natural hormone. It is also referred to as a hormone of darkness, as it relates the information of timing and length of night to the organism as a hormonal signal. During the day melatonin is barely produced at all. Melatonin production occurs through indication from the suprachiasmatic nucleus of the hypothalamus, which significantly regulates the circadian rhythm. If the retina of the eye ceases to perceive enough blue light, then the suprachiasmatic nucleus is informed, which in turn causes the pineal gland to produce melatonin. In this way the hormone is released according to a set rhythm, especially at night, in a cyclical manner into the blood and informs the entire body about the current circadian phase. When the retina captures the first light of day, then the production of melatonin is halted and the production of other hormones begins instead, which are necessary for being awake. This cycle helps to create a circadian rhythm, or 24-hour sleep/wake cycle. Due to the differing light conditions during the seasons, an annual rhythm is created next to the circadian (daily) rhythm. In the winter melatonin is produced and released into the blood for a longer time period than in the summer.
Melatonin possesses a very short half-life period of about 30 minutes. Since it decays so quickly, it must be permanently produced during the night in order to receive a restful night’s sleep, among other things. In humans with a healthy circadian rhythm, melatonin levels rise quickly after dark and then stay elevated at a constant level throughout the night into the early morning. This high level is not only necessary to fall asleep, but also to sleep deeply and restfully. In the early morning the melatonin level decreases again sharply, in order to allow the human to react to the increasing light condition and wake up.
Not only is modern man the only living creature that deviates from its rhythm and makes day out of night, but it is also fact that the older we get, the smaller our nightly melatonin production is, which leads to a shorter signal that is conveyed to the entire body. Often it is not activated until long after midnight. However, at the start of the day the secretion of the hormone stops on time. The result is that the elderly receive the sleep hormone for a shorter period of time, and it is generally available less and less.