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. A prescription-only, timed release melatonin product for people aged 55 and over was approved for use by the European Medicines Agency in 2007, despite having shown only small effects, and in Australia in 2009.
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