A normal and natural pattern of how humans interact with the world relates to our wake and sleep cycle. The human body is adapted to be awake and active during the light, and to sleep during dark periods. Until recently, medical researchers have not fully understood this cycle of alternating wakefulness and sleep as it relates to light.

A healthy sleep cycle is supported by how and when a human is subjected to either light or darkness. When we’re exposed to natural light, nerve pathways in the retina are stimulated. They link from the eye to the hypothalamus in the brain. In the hypothalamus, the suprachiasmatic nucleus (SNA) communicates to other areas in the brain that produce hormones and control the temperature of the body, among other things. These are all factors in whether or not we’re sleepy or ready to be awake.

This cycle of light exposure acts like a clock in our bodies, since natural light is on a regular pattern as the Earth rotates on its axis and orbits the sun. Upon the light exposure, these reactions kick our internal clocks into gear, and help maintain it on a daily basis. Melatonin is one of the hormones that are triggered by light exposure, and for this reasons a lot of sleep research focuses on melatonin levels.

Melatonin a natural hormone is released into the blood by the pineal gland located just above the middle of the brain.  This release of mematonin happens as the sun goes down.  As melatonin levels rise you begin to feel less alert and sleepy.  Melatonin levels stay elevated for about 12 hours.  By 9 am melatonin levels are very low allowing us to be wakeful and productive.

Key Points:

  • 1The SCN takes light information from the retina and shares it with the pineal gland, which starts producing melatonin after dark. Melatonin levels stay active for about 12 hours.
  • 2Since melatonin occurs naturally in food, the FDA has not regulated it as a drug. It can be sold as a food supplement. Drug companies can make synthetic melatonin in factories.
  • 3Studies do not conclude that melatonin increases the total amount of sleep, but that it may be effective in shifting your sleep rhythm.

The SCN works like a clock that sets off a regulated pattern of activities that affect the entire body.


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