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The Science of Melatonin: How Sleep Is Regulated

Learn how the hormone melatonin is related to sleep-wake cycles, circadian rhythms, feeling healthy, and being happy.

Science of Melatonin: How Sleep Is Regulated

When the sun begins to get lower in the sky and the evening gets cooler, we find ourselves beginning to yawn. We start to enjoy the restful evening hours, followed by bedtime. We take these responses for granted, assuming that we naturally get sleepy at the end of our busy day. But what is the science behind this reaction? Why do we find it so challenging to alter this pattern, for instance in the case of night shift workers, or medical personnel on 24-hour shifts? Is there something more going on within our bodies to regulate our cycles of sleeping and waking?

The answer is yes. Scientists are beginning to dive deeper into the study of circadian rhythm and the body’s production of melatonin. Our circadian rhythm is a 24-hour clock shared by most life on earth. This internal clock regulates our sleep/wake cycle and is guided by external cues absorbed through our eyes and skin; cues such as weakening of daylight and dropping evening temperatures tell our brain to begin to produce melatonin, the sleep hormone.

What is melatonin?

Melatonin, sometimes called the hormone of darkness, is a hormone produced by the pineal gland in the brain. It begins to be released when your eyes perceive the change in light at the end of the day. This explains why we sometimes feel drowsy earlier in the winter when the days are shorter, and also why we may want to take naps on gloomy, rainy days. In addition, this sheds light on the challenges that time changes such as Daylight Savings Time, or the crossing of time zones during travel, can leave us feeling off-kilter. It’s because our master clock is having trouble adjusting to a change in visual cues.

Supplementing your natural serum melatonin levels

In a study published by PNAS ( Proceedings of the National Academy of Sciences), the effects of supplementing melatonin in humans during daylight hours at the levels which would occur naturally at night (0.1-0.3mg) showed a marked increase in sleepiness and fatigue when compared to placebo. The study also showed an increase in sleep duration. These results indicate that orally ingested melatonin can mimic the effects of naturally occurring melatonin in humans, making it successful in treating a number of sleeping disorders related to disruption of the circadian rhythm.

Sleep disorders which respond successfully to melatonin supplementation

According to the Mayo Clinic, melatonin supplementation can be safely used to treat the following sleep disorders:

  • Circadian sleep disorders of the blind: Caused by the lack of visual cues of light and darkness, which is the primary signal to the brain to produce melatonin in the evening, and to cease production during daylight.
  • Insomnia: the inability to fall asleep and stay asleep.
  • Jet lag: a disruption of the circadian rhythm caused by crossing time zones during flights.
  • Shift-work disorder: the difficulty in adjusting to the total reversal of the natural circadian rhythm in order to work at night and sleep during daylight hours.
  • Delayed sleep-wake phase sleep disorder: This disorder is commonly experienced by children and young adults. The sleep cycle is delayed generally two hours and the wake cycle is correspondingly delayed, causing them to consistently go to sleep later and wake up later than the norm.

According to most doctors, melatonin has been deemed safe under a doctor’s supervision for short term use to treat any of the above sleep disturbances or to promote sleep for occasional insomnia.

Possible Side Effects

Because melatonin is also found naturally in foods such as milk, strawberries, olives, and tomatoes, it is available over the counter in the US without a prescription. That means it is a supplement that is not regulated by the FDA. Without such stringent regulation, it isn’t always possible to know that the tablet’s dosage indicated on the package matches what’s actually inside. However, it’s important to note that no one has ever reported an injury or illness from an overdose of melatonin. Some minor side effects have been noted. Reported side effects include headache, dizziness, nausea, and drowsiness. Less common side effects include depression, anxiety, tremor, stomach cramps, confusion, and lowered blood pressure.

Potential Health Benefits

Melatonin is also an antioxidant, known to destroy harmful free radicals. Clinical studies have indicated that melatonin can inhibit the growth of certain cancer cells, including breast cancer and melanoma.

Resources: National Sleep Foundation, Mayo Clinic, PNAS, NCBI

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