Man Sleeping with Visible Brain : The sleep-wake cycle is an important circadian rhythm. When it is dark, the suprachiasmatic nucleus directs the pineal gland (located in another part of the brain) to secrete melatonin. This hormone peaks at night and ebbs during the day, and plays a key role in the sleep-wake cycle. Light disrupts melatonin production, and individuals who are exposed to too much light in the evenings, or who work the night shift, may experience problems sleeping as well as disruption in the menstrual cycle and other systems.
Melatonin /ˌmɛləˈtoʊnɪn/, also known chemically as N-acetyl-5-methoxytryptamine, is a hormone found in animals, plants, and microbes. In animals, circulating levels of melatonin vary in a daily cycle, thereby allowing the entrainment of the circadian rhythms of several biological functions.
Many biological effects of melatonin are produced through activation of melatonin receptors, while others are due to its role as a pervasive and powerful antioxidant, with a particular role in the protection of nuclear and mitochondrial DNA.
The full effects of long-term exogenous (dietary) supplementation in humans have not yet been ascertained. Melatonin is categorized by the US Food and Drug Administration (FDA) as a dietary supplement and is not regulated as a pharmaceutical drug, hence its full long-term effects in humans have not yet been ascertained. However, a well-studied prescription-only, prolonged-release melatonin product (Circadin) is available for people aged 55 and over. Prolonged-release melatonin was shown in clinical trials to decrease time to fall asleep, and improve quality of sleep and daytime functioning. It has been approved for use by several agencies globally, including the European Medicines Agency (EMA), the Australian Therapeutics Goods Administration (TGA) the Swiss Agency for Therapeutics Products (SwissMedic), the South Korean Ministry of Food and Drug Safety (MFDS), and the Israeli Ministry of Health (MOH). The approval is based on clinical studies demonstrating positive effects on sleep quality, sleep induction, and next day alertness and functioning.
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