Melatonin is synthesized primarily in the pineal gland, although it also can be produced in the retina and gastrointestinal tract. Melatonin helps regulate circadian rhythms, specifically sleep-wake cycles. These cycles are under the control of the suprachiasmatic nucleus, through which patterns of light and darkness are transferred from the retina to the pineal gland. Melatonin is formed from the essential amino acid tryptophan via serotonin, based on specific patterns. Simply stated, in the presence of light, melatonin production is inhibited; in the darkness, it is synthesized.

Melatonin also can be taken as an exogenous supplement, which is synthesized to be chemically identical to its endogenous counterpart, and is classified as a natural health product by Health Canada or dietary supplement by the United States Food and Drug Administration. Due to its involvement in the sleep cycle, exogenous melatonin has been investigated extensively for sleep disorders.

Difficulties initiating and maintaining sleep...

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