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Melatonin is best known as the hormone that makes sleep possible. Manufactured in the pineal gland of the brain every night, melatonin shuts down the parts of the brain associated with waking activity.
Melatonin “Turns Out the Lights” All Over the Body
Melatonin also “turns the light off” in nerve centers elsewhere in the body. There are melatonin receptors in the gastrointestinal tract. When these receptors are put to sleep, the stomach is less likely to rumble, there colon releases less gas, and stomach acid is less likely to reflux upward into the throat.
There are also melatonin receptors in the skin. The flow of melatonin relaxes the skin so that sebum can flow out of pores to lubricate the skin and smooth out wrinkles, also keeping plugs of this essential skin oil from clogging pores and causing acne.
There are melatonin receptors in the thymus gland. Melatonin tells this part of the immune system to make infection-fighting B cells at night, when more resources are free for this activity.
Blue Light Is the Enemy of Melatonin
This hormone of sleep helps the receptors for light in the retinas of the eye, making it easy to ignore visual stimuli in the bedroom, except for the receptors for blue light, As long as the retina senses even a tiny amount of blue light, the brain cannot make melatonin to let the body sleep.
Before the age of electric light, this property of melatonin helped people deal with seasonal changes in the length of night and day. On long summer days, the brain does not start making melatonin while the sun is still up. On long summer nights, the brain is able to shut down earlier to allow for longer sleep.
In the modern world, this property of the pineal gland is a major problem for getting good sleep. Even the tiniest amount of blue light, the amount of light that can be seen when the eyelids are closed, even from a night light or a hall light shining through the cracks of closed door, stops the production of melatonin. Sleep still occurs, but it is not the whole-body restful sleep that is achieved when the brain is allowed to make melatonin in total darkness.
Many Plants Are Sources of Melatonin
One way to make up for exposure to light at night is to take supplemental melatonin, but supplements are not the only way to get melatonin that your brain does not have to make. Many plants make melatonin. There are clinically significant amounts of melatonin in St. John's wort and in Montmorency cherries. Montmorency cherries manufacture melatonin during the height of summer, when they are exposed to the maximum amount of blue light, and when the humans and animals that eat them are in greatest need of nighttime rest.
Melatonin is also made by a plant known as Harpagophytum procumbens, a creeping desert plant also called devil's claw. This herb could be used as a sleep aid, but its primarily use is as a treatment for pain—and it turns out that the relief of pain is one more way melatonin can improve sleep and improve quality of life. In fact, scientists now also believe that the way St. John's wort treats depression is by relieving pain and inflammation.