melatonin

[ mel-uh-toh-nin ]

noun

, Physiology.

1. a hormone secreted by the pineal gland in inverse proportion to the amount of light received by the retina, important in the regulation of biorhythms: in amphibians, it causes a lightening of the skin.

melatonin

/ ˌmɛləˈtəʊnɪn /

noun

1. the hormone-like secretion of the pineal gland, causing skin colour changes in some animals and thought to be involved in reproductive function

melatonin

/ mĕl′ə-tō′nĭn /

1. A hormone produced in the pineal gland that plays a role in regulating biological rhythms, including sleep and reproductive cycles. In many animals, melatonin also regulates the physiological effects that occur in response to seasonal changes, such as the growth of a winter coat of fur. Chemical formula: C 13 H 16 N 2 O 2 .

Word History and Origins

Origin of melatonin¹

Coined in 1958 by U.S. researcher Aaron B. Lerner and colleagues; from Greek mélā(s) “black” + tone + -in ²

Word History and Origins

Origin of melatonin¹

C20: probably from mela ( nocyte ) + ( sero ) tonin

A Closer Look

Melatonin, a natural hormone manufactured by the pineal gland in the brain, communicates information about light to different parts of the body. It helps regulate biological rhythms and plays an important role in the reproductive cycles of many animals. In humans it is best known for helping to regulate the body's circadian sleep-wake cycle. Melatonin production is affected by light exposure to the eyes; melatonin levels rise during the night and fall during the day, becoming almost undetectable. Though it does not actually induce sleep, melatonin can have sleep-promoting effects. Experiments have shown that at high doses melatonin lowers body temperature, decreases motor activity, and increases fatigue. Melatonin production starts falling after puberty, and it can virtually disappear in the elderly, a phenomenon which could help to explain why sleep disturbances are more prevalent among older adults. Marketed as a dietary supplement and touted as a cure-all for insomnia, jet lag, and even cancer and aging, the overall effects of melatonin on human health are still largely unknown.

Example Sentences

Taking melatonin supplements, eating a healthy diet and reducing alcohol intake before the time change and for a short period afterward can help to alleviate symptoms of sadness or depression, Palinkas said.

From Los Angeles Times

During those sessions, saliva sampling allowed measurement of the phase and amplitude of melatonin, a hormone that regulates sleep-wake cycles and cortisol secretion, the body's main stress hormone.

From Science Daily

They found melatonin, a hormone that helps with the timing of circadian rhythms and sleep, is secreted earlier in women than men.

From Science Daily

Continuous exposure to these light sources at night can suppress melatonin production, a hormone that promotes sleep.

From Science Daily

By evening, levels of a hormone called melatonin begin to surge, triggering drowsiness.

From Seattle Times