Circadian Rhythm Sleep Wake-Cycle

Introduction

Have you ever wondered why you feel sleepy around your regular bedtime? It’s because of the circadian rhythm. In this blog, we gonna see how circadian rhythm makes us sleep and wake with some tips to follow. circadian rhythm sleep wake cycle

Let’s get into the short history section before moving on to the relationship between circadian rhythm and the sleep-wake cycle. 

History of Circadian rhythm 

Ah ha! Don’t skip it. A small Evolutionary story will make you understand the Circadian rhythm better. 

Principle of the Universe: We are part of the universe. So, any change that occurs in the universe will also occur in our bodies. 

Earth’s rotatory dance: We know that our solo dancer – Earth takes around 24 hours (a day) to rotate around its axis. This rotation causes changes in the environment throughout the day such as changes in light, darkness, temperature and humidity.

Survival of the fittest: The one who adapts to environmental changes will survive better than the one who doesn’t. 

Birth of the circadian rhythm: As we are part of the universe, we living things need to adapt to environmental changes caused by Earth’s rotation to survive better. So our body developed a cycle called the Circadian rhythm, which syncs with the changes caused by the Earth’s rotation every 24 hours. 

In simple words, Earth’s rotatory dance created a rhythm within living organisms.

So, our body changes and adapts to environmental changes to maintain a balanced state with the universe and at the same maintain a balanced state within the body.

If we don’t adapt and sync with the environmental changes or lose the balance within our bodies, we will be dis-eased.

“The concept of Survival of the fittest gave birth to the Circadian rhythm” – “MayaSiddha”

Circadian rhythm sleep wake cycle

What does the term circadian rhythm mean?

Circadian means “approximately a day” and here rhythm means “sync in time or to flow” and also means “an activity that repeats in the same order”.

Circadian rhythm: Circadian rhythm is the natural physical, mental and cell-level changes that occur in our body the entire day, which syncs in time with the environmental changes caused by Earth’s rotation.

In simple words, like hair blowing with the air, Circadian rhythm means to flow with the environmental changes each day in the same order.

What maintains the Circadian rhythm?

Circadian rhythm is regulated by the Suprachiasmatic nucleus of the brain, which is also called the Circadian clock. 

The Circadian rhythm is the tick-tock of the Circadian clock. But this clock is not accurate, it doesn’t know whether 24 hours have been over or not. Now, a question arises: what makes the clock run for 24 hours?

Every cell in our body has a rhythm that syncs with the rhythm of the circadian clock.

• Resetting the Internal Clock

External factors, particularly light and darkness influence circadian rhythm. It is also influenced by food, stress, temperature etc. When sunlight falls on the earth, our body receives it and resets the clock that generates the circadian rhythm. 

That means our body starts to repeat its daily work from the beginning of the cycle as soon as it receives the signal from sunlight. 

Research shows that even without sunlight our Circadian clock will work regularly but not for 24 hours, a little more than that. Sunlight is the main factor that resets our inaccurate internal clock every day.

How does our body receive the sunlight? 

• Eyes are windows 

The sunlight enters through our eyes (even when closed) and is received by the light-sensitive cells present in the eyes and from there, it passes to the brain, where it signals the circadian clock to reset.

Research found that Melanopsin, a blue light-sensitive protein is another light-sensitive cell present in our eyes. It is present in both normal and blind people, so blind people who have this protein will be able to regulate the Circadian rhythm. 

Circadian rhythm sleep wake cycle

Circadian rhythm and sleep-wake cycle

How does the circadian rhythm make us sleep?

A few hours after sunset, a hormone called Melatonin is released from the Pineal gland which is located in the brain. This hormone announces to our body and brain that it’s time to start the sleep cycle, like an alarm that rings in a company which indicates the shift is over.

Melatonin is only an initiator of the sleep cycle; it won’t be present throughout it. This means taking melatonin pills or having melatonin-rich foods will only prepare your body to sleep, like making the bed.

Unfortunately, even after sunset, our world is filled with bright lights, and exposure to them makes your body think it is daytime. So, it delays the onset of melatonin secretion which alters the sleep time.

Studies have shown that other than sunlight, blue light will also influence the circadian rhythm, because of the Melanopsin protein. So using mobile phones and laptops and being exposed to bright light after sunset delays the onset of melatonin production. 

It also means our rhythm is out of sync with the environmental changes. This is one of the reasons why you deal with sleep disorders and other health issues. 

Melatonin, also called dark hormone, is produced only in the dark.

How does the circadian rhythm make us wake? 

After receiving the signal from sunlight, the circadian clock presses the brake pedal on the pineal gland which stops the melatonin secretion. So, our body stops the sleep cycle as the power button is turned off. As the sleep cycle is off, you will wake up.

Now our body starts to secrete various chemicals that signal various parts of the body to start their cycle. One of the chemicals called Cortisol, a stress hormone is produced, which prepares our body to face everyday stress caused by the environment.

If you are in sync with the Circadian rhythm, you will sleep and wake at the regular time each day.

Circadian rhythm sleep wake cycle

Summary 

Our body developed a cycle called circadian rhythm to sync with the environmental changes caused by the Earth’s rotation every 24 hours to survive better. This rhythm is regulated by the circadian clock/suprachiasmatic nucleus present in the brain. The clock resets and works in a 24-hour format with the signal received from the sunlight. 

A few hours after sunset our body produces melatonin, a dark hormone. This chemical signals our body that it’s time to sleep and it starts the sleep cycle. This sleep cycle continues until our body receives the signal from sunlight. 

As soon as our body receives the sunlight it stops the melatonin production, which stops the sleep cycle and we will wake up. The clock resets and our body starts to repeat its regular work from the start like we doing a step-by-step skincare routine. 

Circadian rhythm sleep wake cycle

Tips 

1. Follow a healthy circadian rhythm.

2. Sleep and wake at the same time each day.

3. Keep your room dark as much as possible to produce enough melatonin to start your sleep cycle.

4. You can wear an eye mask if you can’t keep your room dark.

5. Use dim orange/yellow light after sunset. This colour dim light has little effect on the circadian rhythm.

6. Avoid using mobiles, laptops, computers and being exposed to bright lights at least 4 hours before bed.

7. Turn off wifi, internet and radio before bed.

8. Don’t expose yourself to bright lights when you wake up in the middle of your sleep.

9. Leave a gap in your room for the sunlight to enter, which is important to reset your clock.

Circadian rhythm sleep wake cycle

Reference 

1. Walker, M., & West, S. (2017). Why we sleep: Unlocking the power of sleep and dreams. Unabridged. New York, Simon & Schuster Audio.

2.    Shook, S. (2022). The science of sleep. Kapi’olani community college.

3.    Zisapel, N. (2018). New perspectives on the role of melatonin in human sleep, circadian rhythms and their regulation. British Journal of Pharmacology, 175(16), 3190-3199. https://doi.org/10.1111/bph.14116.

4.    Blume, C., Garbazza, C., & Spitschan, M. (2019). Effects of light on human circadian rhythms, sleep and mood. Somnologie, 23(3), 147-156. https://doi.org/10.1007/s11818-019-00215-x.

5.    Chaix, A., Zarrinpar, A., & Panda, S. (2016). The circadian coordination of cell biology. The Journal of Cell Biology, 215(1), 15-25. https://doi.org/10.1083/jcb.201603076.   

6. Rafique, N., Al-Asoom, L. I., Alsunni, A. A., Saudagar, F. N., Almulhim, L., & Alkaltham, G. (2020). Effects of Mobile Use on Subjective Sleep Quality. Nature and Science of Sleep, 12, 357-364. https://doi.org/10.2147/NSS.S253375.

7.    Alshobaili, Fahdah A.1,; AlYousefi, Nada A.1. The effect of smartphone usage at bedtime on sleep quality among Saudi non- medical staff at King Saud University Medical City. Journal of Family Medicine and Primary Care 8(6):p 1953-1957, June 2019. | DOI: 10.4103/jfmpc.jfmpc_269_19. 

8. Reddy S, Reddy V, Sharma S. Physiology, Circadian Rhythm. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519507/. 

Circadian rhythm sleep wake cycle