What Are Circadian Rhythms? We Define Them

Your body really is amazing. Not only is it largely self-regulating (breathing and blood flow are, for most of us, automatic processes) it also contains a pretty accurate way of measuring time: the circadian rhythm.

Circadian Rhythms Defined

Circadian comes from the latin and means, roughly, around (circa) the day (dian from diam which means day) and it’s a pretty special quality. It helps your body understand what time of day it is and controls not just sleep but also your body temperature, your hunger, your metabolic rate and the release of various hormones.

For a long time it was assumed that the sun and its light were the things that determined when we slept and when we were awake but a brave experiment run in 1938 showed otherwise.

Experimenting In The Dark

Professor Nathaniel Kleitman and his research assistant Bruce Richardson (both from the University of Chicago) spent 32 days live  in the Mammoth Cave in Kentucky. They chose the cave because it was deep and dark, so much so that no detectable sunlight reached the parts they chose to set up camp.

For the period of the test they ate, slept and worked in the dark and found that their natural sleep and waking cycles remained pretty constant. They wondered if the lack of sunlight would mean that they would not know when to sleep and when to be awake and that their bodies would lose the daily rhythm. It turned out not to be true and they discovered that even in the dark they were awake for about 15 hours and slept for about 9 every day. This was their Circadian Rhythm at work, entirely independent of daylight.

They also discovered that their rhythm was not exactly 24 hours in length and now we know that our rhythm is approximately one day not exactly so. Our bodies have developed a clever mechanism to reset our rhythm. It is the suprachiasmatic nucleus which lives towards the back of the brain and use light samples to correct our circadian rhythms, bringing them back to a reliable 24 hour cycle.

Morning Larks vs Night Owls

Interestingly, our rhythms are not identical. Around 40% of people are morning people. They are happy to wake early in the morning, often and dawn, and find themselves most productive in the early period of the day. Around 30% of the population are night people. They find themselves working best late in the evening and prefer to get up late. The remaining 30% are somewhere in between1See Why We Sleep by Matthew Walker (Penguin, 2018). (Check out this article on how to become an early bird.)

It’s not clear why we evolved this way and one theory is that the differences helped preserve tribes who lived together. Some were able to get up early whilst others were able to stay up late at night and, together, they could keep watch for threats for longer.

Whatever the case, modern work schedules make life hard for people who like to stay up late. Work days are typically structured around the daytime and social activities are scheduled in the evening. However, if you’re a night person, you can spend much of your working day with a brain struggling to escape its sleep state making you far less productive than your morning person colleague. Find out how to become a morning person here.

Conquering Jet Lag

Circadian rhythms are one of the big reasons we suffer from jet lag. Our bodies find themselves in situations where the day is longer or shorter than our bodies think it will be and so sleep can be difficult to come by. Because daylight is only part of the equation, adjustment can be slow and it has been calculated that the suprachiasmatic nucleus can only adjust your body clock by about an hour every day.  Adjusting to a new timezone can take longer than we expect or plan for.

One solution is to take melatonin, a hormone that on its does not create sleep. Rather it acts as a signal to corral the body into preparing for sleep. It’s often available in US chemists and might be useful next time you travel if you want to try and reset your circadian rhythm as quickly as possible.

Another solution is Rise – Sleep Better which will help your mind and body relax before bedtime.

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Tom Williams

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