Melatonin is a hormone primarily released by the pineal gland in the brain at night, and has long been associated with control of the sleep–wake cycle. In mammals, including humans, the circadian system is organized into a hierarchical manner with a central pacemaker in the suprachiasmatic nucleus (SCN) of the brain’s hypothalamus. The SCN synchronizes the circadian physiological and behavioral rhythms, including sleep and wakefulness, temperature, feeding, neuroendocrine and autonomic effects, with the 24-hour periodicity to match the environmental light–dark cycle, thereby orchestrating an optimized internal temporal order. Light is the primary stimulus for tuning (entraining) the SCN rhythm period via eyes and phase with the external environment. A neural output signal, generated by the SCN, induces the synthesis of melatonin at night by the pineal gland. The hormone is released into the third ventricle in the brain and subsequently the circulation throughout the body. Light, in addition to tuning the SCN, acts to inhibits melatonin synthesis. Because melatonin is metabolized rapidly, plasma melatonin levels are low during the day and high during the night. Melatonin is an important physiological sleep regulator in diurnal species including humans.


Health benefits

As a dietary supplement, it is often used for the short-term treatment of insomnia, such as from jet lag or shift work, and is typically taken orally. Clinical studies have shown that taken melatonin can induce sleep and lower body temperature to help to improve sleep quality.

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