What is the circadian rhytm and does it impact your sleep?

circadian rhytm

The definition of the circadian rhythm:

The natural cycle of physical, mental, and behavior changes that the body goes through in a 24-hour cycle.

Your circadian rhythm is your internal 24 hour body clock. The word circadian comes from the Latin words: "circa" and "dian". Circa means around or approximately. Dian or diam means day. So circadian means approximately one day.

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The word rhythm in the sense used here, means a pulse or a cycle repeating itself, in a given interval. Thus, the circadian rhythm means an approximate 24-hour cycle.

This cycle affects i.a. your sleep, body temperature, hormone release and metabolism. You may see it referred to as: 'diurnal rhythm' as well.

Our circadian rhythm is reset with every sunset. Other factors can influence it as well. Those might be i.a. food or regularly timed social interactions. Without any resetting triggers from the outside world, our circadian rhythms would approach a 25-hour cycle.

The circadian rhythm and your sleep

This diurnal or circadian rhythm affects your sleep wake cycle. It helps your brain to know, when it is time to be awake, and when it is time to sleep.

The first sunlight of the new day kick-starts and resets your circadian rhythm. The brain stops the release of melatonin. Melatonin is a hormone which informs your body, that it's now time to prepare for the night.

At the same time, your brain releases a small amount of the hormone cortisol, which helps you wake up.

If your circadian rhythm gets messed up, you'll have problems falling asleep. That's mainly because melatonin release is out of sync with your physical environment. This is why you suffer from e.g. jet lag or a circadian rhythm sleep disorder. This sleep disorder is also known as delayed sleep phase disorder or circadian rhythm disorder.

Morning person ... and biological rhythms.

Even healthy peoples circadian cycles can be slightly out of sync. This is a result of evolution. The sun rises at the same time, for everyone in a tribal community. You may wonder why morning lark and night owl chronotypes even exist.

The best current explanation is known as the sentinel theory. If the whole tribe went to sleep at the same time, that would give it an 8-hour vulnerability window.

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The tribe as a whole is fitter for survival, if some members of the tribe go to sleep early, and others go to sleep later. The morning lark members would then also wake up earlier. As a result, this significantly reduces the vulnerability window, where everybody is asleep. Tribes, with both kinds of chronotypes, had better chances to survive evolution.

We have arranged today's society in favor of the morning larks. Night owls are more exposed to problems with sleep and circadian rhythm disorders. That's not fair - we should show them more gratitude. They helped our genes survive.

Plant's got rhythm

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Most living creatures builds their own internal biological rhythms. Even plants have a circadian clock. The first person to prove a circadian rhythm in plants was Jean-Jacques d'Ortous de Mairan.

He placed a 'Mimosa Pudica' in complete darkness in a cupboard. Even when left in complete darkness, the plant continued to expand its leaves in the morning. And, needless to say, collapsed them at night.

This way he proved that, the plant knew when it was morning, and when it was evening. The sun could not trigger expansion of the leaves, when it was in complete darkness. The plant had to have an internal biological clock.

Scientists' also got rhythm

In 1938 scientists Kleitman and Richardson spend more than a month in a cave. The cave was so deep, that no sunlight would penetrate it, to the deepest levels.

During all this time, they did not get exposed to sunlight. They did this to find out, if their circadian rhythm remained the same, as for those outside.

The result was, that their brains still followed a pattern of roughly 15 hours of sleep, and 9 hours of sleep. It turned out, that their both of their circadian rhythms drifted to be just over an exact 24-hour cycle.

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It's the same result, when scientist examine people living in the arctic. During the polar night, it is dark for nearly half a year.

Blue light and your sleep

Scientific studies prove, that it is the light in the blue spectrum, that resets our circadian clock. Some believes this dates all the way back to when our earliest predecessors lived in blue water.

When your brain registers blue light, it's pre programmed to wake you up. That's why e.g. working with a computer, reading from a tablet or even watching TV before going to bed is a really bad idea.

That's especially true if you have problems falling asleep or tend to wake up to early. Both these are signs, that your circadian rhythm is out of sync. When you brain registers the blue light from those screens, it believes it is morning, and then it pauses the release of melatonin. Furthermore, to add insult to injury, it also makes your brain release a little cortisol.

If you must work on the computer at night, you could benefit hugely from wearing some blue light blocking glasses.

Natural light

In one scientific experiment, there were 8 test persons, with an average age of 30. The experiment ran for 2 weeks. In the first week, all the test persons should follow their usual daily routines.

In the second week, they went camping in the mountains. No artificial lights were permitted during this week. No cell-phones, no flash-lights. Their only sources of light, were daylight and the campfire.

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Scientists measured their activity, their exposure to light and their melatonin levels. After one week, the participants had all adjusted their circadian rhythm to the sun. Their melatonin production peaked 2 hours earlier in the mountains. The participants also reported, that it was easier for them to both fall asleep in the evening.

What can you do, if you circadian rhythm is out of sync, and you can't go camping in the mountains? Try to expose yourself to a little daylight every morning. That will help to adjust your internal body clock. Also, if you go out in the afternoon, consider wearing sunglasses.

May you rest long and safe in the arms of Morpheus.

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