What is the Circadian Rhythm?

human biological clock

The Circadian Rhythm, also called the body clock, refers to physiological and behavioral processes in biological organisms (plants, animals, and microbes) that align closely to a 24-hour cycle. In animals, with specific emphasis on human beings, this cycle is primarily affected by light and darkness. This internal ?clock? is located in the central part of the brain called the hypothalamus. It is true that our bodies function based on this daily clock and this is why some of us would want to sleep when the sun sets and wake when the sun rises. At some point, you may have woken up a minute before your alarm rings? Isn?t that interesting? It just goes to show that our body clocks are pretty accurate, and are definitely in harmony with the environment.

How the Circadian Rhythm?Works

circadian rhythm labeledThe body clock controls several biological processes taking place in your body. It regulates your feeding and sleeping patterns, temperatures, brain waves, production of hormones, regulation of insulin and blood glucose, regeneration of cells, production of urine, and alertness of the body among many other things. Your sleep and overall health are dependent on your internal body clock. However, if it is disrupted, your sleeping and eating habits are disturbed. In fact, research reveals that disruption of circadian rhythm causes adverse side effects such as obesity, cardiovascular changes, and other neurological problems such as bipolar disorders and depression.The circadian rhythms are controlled by a set of neurons in the brain called the SCN (Suprachiasmatic Nucleus). This group of about 20,000 nerve cells is located in the hypothalamus, just above the optic nerve.

Larks, Owls and Hummingbirds

Light is the most important driver of the circadian rhythm. If you sleep in a dark room, the chances are high that you can sleep longer than usual. Studies have shown that people with shorter circadian rhythms wake up earlier in the morning than those with longer circadian rhythms. To make this concept relatable, every person has what is called a “chronotype”–their own internal timesheet. Each chronotype describes a different sleep pattern.

which bird are you

Persons who rise early in the morning and have more energy at the beginning of the day are classified as larks (since these birds are awake at the crack of dawn). Persons who are more active in the late evenings and nights and tend to sleep later as classified as owls (which are more nocturnal). Note that this classification does have some flexibility to it…for example I was an owl in college, but became more of a lark as I moved into the world of work. If you don’t quite fit either of the two, then it means you’re somewhere in the middle, and would be categorised as a hummingbird.

Naturally there are some advantages and disadvantages to each but at the end of the day, each class can learn to manage their schedules in a way that is best fit without too great of a compromise to healthy sleep habits.

Hormonal Influences on the Circadian Rhythm

The most critical hormones affected by the body clock that influence sleep are melatonin and cortisol. Melatonin (known as the ‘sleep hormone’)?is produced in the pineal gland located in the brain, and is responsible for lowering the body temperature and causing drowsiness. Its concentration is lowest in the morning and highest towards the end of the night. The SCN controls the production of this hormone, ensuring levels elevate throughout the evening into the night–hence helping you to fall asleep.

The adrenal glands produce cortisol (also known as the ‘stress hormone’). Cortisol is vital in maintaining levels of?blood glucose in the body. It is highest in the morning and lowest throughout the night. If you find yourself waking up hungry at odd hours however (say, between 1am and 3am) then you may not have nourished your body enough prior to bed. In that case, low blood glucose triggers a warning to the brain of low energy levels, elevating cortisol production, and bumping you awake?so as to get something to eat.

Since cortisol?controls your stress response, it goes without saying that lowering it before bedtime is beneficial. It’s good to try relaxation techniques to help lower this, such as yoga, breathing exercises, prayer and/or meditation (with or without binaural beats).

melatonin and cortisol cycles

Image credit: CoachMikeBlogs.com

Note that cortisol is an important counterpart to melatonin–it helps suppress immunity and inflammation, while melatonin helps to promote the immune response. Knocking these two out of whack can cause serious issues with health such as poor sleep, low energy, weight gain, and in some extreme cases, even cancer.

How the Circadian Rhythm Keeps Time

Our circadian clocks check their accuracy levels every day by the use of Zeitgebers (German for ?time-givers?) or the light-dark cycle. When you are exposed to light, special?ganglion cells in the retina are?stimulated. These ganglion cells contain a light-sensitive pigment referred to as melanopsin which is very sensitive especially to short-wave blue light. This is why you can easily note daylight even when your eyelids are closed. It is also the reason why it?s not recommended to watch TV or play around with mobiles immediately before bed! Their screens emit blue light, which promotes wakefulness and thus interferes with sleep onset.

no devices before bed

Environmental cues such as light help to regulate and/or reset our circadian rhythms. It should be noted however, that further studies have revealed that the circadian cycle works unaffected by light such that even if you are in an entirely dark room, you can note when to sleep or wake up. The light-dark cycle therefore acts to resynchronize the body to eliminate simple timing errors.

With today’s?busy modern lifestyle, we are forced to adjust to different conditions very rapidly. If you are a regular traveler, or a shift worker, then you are likely to be?disrupting your circadian rhythm with disturbing frequency. Be warned that chronic disruption can lead to serious sleep disorders like insomnia. By understanding how circadian rhythm works, you can make properly informed decisions on how you can solve various sleep related disorders. In fact, you can employ several measures to reinforce your natural body sleep patterns. Experts recommend avoiding stimulants especially 4-6 hours before bedtime, daily naps and controlling light around you when asleep.

How’s your sleep cycle these days? Did this article help you to gain a better understanding? I’d love your feedback so please leave me a comment below!

Sleep well until next time.



  1. SheFashion

    Wow, Your page is fascinating. it just never crossed my mind on how I got to realize that it’s morning (time to wake up) but by reading your page I have learned al all. I should say that I function more at night, so, in short, am an owl :).
    Having to find out that we having sleeping hormones makes me wanna know more and share this information.
    Thank you so much for this wonderful new information. consider your page shared ๐Ÿ™‚ ๐Ÿ™‚

    1. Joshua (Post author)

      Thanks a lot SheFashion, it means a lot to me that you’ve taken the time to share this post. I thought it was important that people understand that a lot more happens during sleep than we realise most of the time. Like yourself, I was once an owl, and I had no real issues with it…running around after 2am in the morning. I kind of miss that because of the quietness and solitude–I could get a lot done at night even moreso than in the day. I’m more of a lark now though…mainly because my job requires it ๐Ÿ™‚ . Feel free to check out my other posts as well, there’s a lot more stuff to learn!

  2. Lee

    Very interesting article and i honestly learnt a lot from it. I didn’t realise that being on a devise was so bad for you prior to sleeping, it normally sends me right off but i will think twice about doing so this evening.
    It also very interesting to learn about your body waking you up in the night if you haven’t had enough nutrition.

    Many Thanks


    1. Joshua (Post author)

      I’m glad you found this informative Lee. Devices with full colour screens can be terribly poor and helping us sleep, but I should point out that readers that utilise e-Ink, such as the Kindle, aren’t bad at all. If the backlighting is also directed parallel to the screen (preferably) then you can actually reduce your exposure and thus get to sleep without having to really worry much about blue light interference.


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