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14.8: Melatonin

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    Source and Control of Secretion

    Melatonin is secreted by the pineal gland (Figure 14.1). Its secretion seems to be controlled by alterations in brain impulses caused by light detected by the eyes. Since an increase in light exposure inhibits melatonin secretion, blood levels follow a circadian rhythm, with low levels during the day and high levels at night. Secretion is also influenced by the qualities of light, including time of exposure, light intensity, and wavelengths (colors). Melatonin is also produced by the retina, where it seems to have an antioxidant effect.


    Melatonin seems to inhibit sexual maturation until the teenage years. Its circadian rhythm regulates circadian rhythms, including sleep and body temperature. Also, oscillations in melatonin seem to affect psychological parameters such as mood and depression. Therefore, adverse effects from alterations in circadian secretion may occur in people who receive little exposure to natural light, who are exposed to different wavelengths of light (e.g., fluorescent light), or who receive exposure to artificial light very different from the natural schedule of daylight.

    Melatonin travels easily to all body parts. It is a powerful antioxidant. Also, it stimulates production enzymes that remove *FRs, and it promotes the formation and effectiveness of other antioxidant substances. It seems to have a major role in protecting the brain and other body parts (e.g., lungs) from *FR damage.

    Age Changes

    Aging is accompanied by a decrease in the amplitude of the circadian rhythm of melatonin, which results from a decrease in the maximum blood levels attained at night. This leveling in rhythm may influence age-related changes in circadian rhythms such as sleep patterns and hormone secretion (e.g., GH, testosterone).

    Melatonin supplementation

    Using melatonin supplements has become popular. Melatonin is inexpensive, easy to obtain and can be taken orally. Though it is a hormone, its sale and use are not regulated like most other hormones. Melatonin is used commonly to reduce the effects from "jet lag" and to help establish or reestablish circadian rhythms. Some people take melatonin to slow, stop, or reverse age changes because it is an antioxidant, caloric restriction helps sustain melatonin levels as it increases ML and XL, and melatonin supplements increase ML in animals. Hazards from melatonin supplementation include disruption of circadian rhythms, unbalancing other hormones, and overdosing or toxicity from the unregulated production and testing of melatonin supplements.

    This page titled 14.8: Melatonin is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Augustine G. DiGiovanna via source content that was edited to the style and standards of the LibreTexts platform.