English subtitles for clip: File:Melatoninausschüttung und Körper-Rhythmus.webm

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In brightness, the receptors on our retina pick up light

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and the production of the hormone melatonin is suppressed.

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A complex control organ in our brain is responsible for this.

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The pineal gland regulates the day-night rhythm of the body

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(circadian rhythm) by releasing melatonin.

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So when it gets dark and hardly any light

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hits the eyes, it secretes melatonin.

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The increased melatonin level makes us tired, lowers appetite, body temperature and blood pressure.

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This is not unique to humans, but works similarly in almost all vertebrates.

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Fish are particularly well studied in this regard.

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Even small amounts of light lower their melatonin levels.

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And that, in turn, affects their growth, immune defenses, and reproduction.

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So they are particularly affected by artificial light at night.