What are Circadian Rhythms and How Do They Impact Sleep?

First added 22nd July 2021

By Lewis Ridley 

5 min read

Sleeping is one of the joys of life. There's nothing better than snuggling into a warm duvet to catch a long night of Zs, especially when you've had a hard day's work. However, if you find yourself sleeping irregularly or start to notice you're waking up at odd times, your circadian rhythms could be to blame.

Circadian rhythms govern your sleeping pattern more than you think. But what are they? And how do they influence our sleep? In this article, we'll be answering all these questions. If you want to learn more, continue reading.

What are Circadian Rhythms?

Your circadian rhythms control your sleeping and waking schedule. They help you fall asleep at night and rise in the morning. It's tied to your 24-hour biological clock, which everyone and nearly all living creatures have. Due to its influence, it is sometimes referred to as the "sleep-wake cycle".

Circadian rhythms interact with light and darkness, triggering a number of different systems and hormones. These systems can either make you wake up or send you to sleep.

In fact, circadian rhythms and biological clocks play such a large role in sleep. There is an entire field of study dedicated to it. This is known as chronobiology. If you're looking to learn more about them, this is the field of study to choose.


How Do Your Circadian Rhythms Work?

As previously stated, circadian rhythms react with light and darkness, which trigger internal responses in the human body. The changes result in different hormones releasing as well as temperature changes. Let’s explore some of these changes and how circadian rhythms work.

Hormone Changes

Throughout the day, hormones are influencing your behaviour, and many of them are governed by your circadian rhythms. Your internal clock has peaks and troughs throughout the day, which makes you feel either alert or tired. This is why some people feel more awake in the morning and start to "crash" in the evening.

A few core hormones that play a role in your circadian rhythm include melatonin, cortisol, and adenosine. These hormones either increase or decrease during the day to help what you know as waking and sleeping.

Melatonin is a sleep-inducing hormone your body releases closer to sleep and during sleep. It also suppresses sleep during the day. Cortisol is a stimulating hormone that is linked to stress responses. This hormone helps you wake up and feel alert in the morning. Adenosine is another hormone that triggers sleep. This builds up throughout the day but can be suppressed through caffeine and other stimulants. Once adenosine and melatonin have built up enough, you will naturally fall asleep.

Light Sensitivity

Circadian rhythms are heavily influenced by light and darkness. This is a result of specific cells in the brain which react to light when the eyes are exposed to the sun (or an object with a similar lux output).

These light-sensitive cells are present in the suprachiasmatic nucleus (SCN) near the hypothalamus. When this area is triggered, it will fire signals to other parts of the brain, including the pineal gland – the main gland responsible for the release of key hormones (such as the ones described above).

As a result of these light cells, your sleep and wake cycle follow typical daytime-night-time patterns. However, if you work nightshifts or have insomnia, things can start to go a bit haywire, as you’ll see later in this article.

How Do They Impact Your Health?

As we’ve already detailed, circadian rhythms primarily impact sleep. However, they also have an indirect impact on nearly all other systems in the body. Here are a few ways circadian rhythms affect the rest of the human body:

  • Metabolism and Weight: Research has indicated your metabolism and weight are heavily influenced by the flow of your circadian rhythms. Your metabolism tends to go up and down at different periods of the day, alongside your natural waking-sleep cycle. Therefore, if you’re looking to lose weight, understanding this concept could be helpful.
  • Mental Health: Mental health disorders, such as depression, have been linked to the ebbs and flows of circadian rhythms. Serious psychiatric disorders and neurodegenerative disorders have even been linked. However, mental health problems can also occur because of faulty circadian rhythms. The chain of causation isn't always clean cut.
  • Immune System: Finally, circadian rhythms have an influence on your immune system, which in some cases can been linked to cancer prevention. It seems circadian rhythms are just as important for our health as they are for sleep.

Can Circadian Rhythms Fall Out of Sync?

Yes. Your circadian rhythms are influenced by your lifestyle and environment. If you don't follow the natural tendencies of your 24-hour clock, small (and sometimes serious) issues can follow.

The core culprit behind a faulty circadian rhythm is sleeping and waking times. Therefore, if you have overnight or alternating shifts, you can start to change the times your body gets ready to sleep. The same can go for long working hours or if you like to stay up late (hitting the town, watching movies, etc.). All these late-night events can start to take a toll on your circadian rhythms.

In fact, there is an entire disorder called Shift Work Disorder, which is used to categorise problems arising from poor working hours.

According to The Sleep Foundation, here are a few other potential ways your rhythms can fall out of sync:

  • Jet Lag
  • Delayed Sleep Phase Disorder
  • Advanced Sleep Phase Disorder
  • Irregular Sleep-Wake Rhythm Disorder

What Can Happen if Your Rhythm is out of Sync?

If your circadian rhythm falls out of sync, you’ll know about it. The typical symptoms include feeling sleepy and lethargic. Additionally, you’ll struggle to fall asleep at normal times. Instead, you’re likely to fall asleep too early and wake up in the middle of the night, or you’ll fall asleep too late and wake up midday. For many of us, this describes our days at University nicely!

With these irregular patterns at play, sleep can become fragmented and low-quality. Resulting in poor sleep and sometimes insomnia. If the negative patterns continue, further health complications can occur.


How to Reset Your Circadian Rhythms

Everyone has probably experienced a problematic circadian rhythm at some point in their life. The good news is if you're currently suffering from an out-of-sync circadian rhythm, there are a few things you can do.

The first thing is to start sleeping at normal times. This may sound obvious but it's important to get your body back into the natural rhythm of sleeping at night and waking in the morning. To achieve this, try setting a bedtime and an alarm in the morning. Additionally, avoid daytime naps, especially if it's getting late.

Caffeine and stimulants are your enemy here. If you need caffeine to keep you going during the day, try and make sure it's consumed earlier in the day to reduce night-time disruption.

If you want to help your sleep and other parts of your health, exercising daily can provide a ton of benefits. Just a few minutes a day can help cardiovascular health and help your body rest when the time is right.

How to Maintain a Healthy Circadian Rhythm

Once you have your rhythms in sync (or if they were already in sync), maintaining them can help prevent any problems in the future. By keeping a healthy sleep schedule and taking care of your resting period, you can remove a lot of restless periods in the day, weeks, or months to come.

If you want to perfect your rhythms, here are a few tricks you can try:

  • Maintain a healthy sleep schedule
  • Go easy on the caffeine and stimulants
  • Get sunlight early and often
  • Get some exercise in daily
  • Prevent exposure to screens before bed

As you can see, many of these tips are similar to the strategies used to get back into sync. Nonetheless, maintaining a healthy circadian rhythm is important and by using some of the tips above, you can ensure you'll feel well-rested and alert during the daytime.

Closing Thoughts

Circadian rhythms are a natural part of the human condition. They help to wake the body up and help it prepare for bed. Without this system, hormones wouldn't get released on time and you would end up sleeping and waking at incredibly strange times.

However, although this is an ancient system present in most animals, it can still fall out of sync. This can lead to a whole host of problems. With the tips and tricks we've included above, you'll be on track to fixing your cycle and achieving a heavenly sleep schedule.

Of course, circadian rhythms aren't the only thing contributing to a sound sleep. Your bed and mattress matter too! If you need any further advice when it comes to sleep and slumber, get in touch with the Sleep and Snooze team now.


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