What Is Circadian Rhythm?

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written by sleep expert Lauren Hall

What Is A Circadian Rhythm? Everything you need to know:

Our Circadian Rhythm is the fundamental part of our sleep and wake schedule. Circadian rhythms are 24-hour cycles that are part of our body’s internal clock, there are many different biological rhythms, but our circadian rhythms or sleep-wake cycle is the best-known one of them all.

But what are Circadian Rhythms?

Circadian Rhythms are the process that originates within an organism and respond to the environment. It is our master clock within our brain that is directly influenced by environmental cues, especially light which explains why we feel alert in the day and sleepy at night.

When your circadian rhythm is properly aligned, it can promote consistent and restorative sleep, but when thrown off, it can cause circadian rhythm sleep disorders like insomnia. Circadian rhythms play a super important role in our mental health and physical health in order for us to feel well-rested.

Want to hear something cool?

Our circadian rhythms are governed by exogenous zeitgebers (EZ) and endogenous pacemakers (EP)– don’t worry, you don’t need to know the name. Our EZ is an environmental factor that causes us to feel drowsy when it’s dark and alert when it is light, as daylight affects our cycle.

Then the EP is the internal biological clock that is constantly running, but the environmental factors can reset our circadian rhythm and cause it to become disrupted. But there are many studies that prove that our circadian rhythm cannot just be overridden by our external factors.

But if you’re confused, don’t worry, it’s just an interesting fact! Enough of me rambling on; let’s jump in!

circadian rhythm

How Does Circadian Rhythm Work?

Circadian Rhythms are responsible for helping make sure that the body’s processes are all optimized at various points throughout a 24 hour period. They are physical, mental, and behavioral changes that follow this period. Circadian Rhythms are influenced by the environment, such as light and day and our body’s internal body clock.

One example of how circadian rhythms work is through our exogenous zeitgebers, which are external factors that influence our cycles, such as light and darkness. Light-related circadian rhythm is sleeping at night and being awake and alert during the day.

But circadian rhythms are not only present in humans but also in animals and plants. A study of chipmunks with suprachiasmatic nucleus connections was removed, then they returned to their natural habitat, and because of this alteration, the sleep/wake cycle of the chipmunks was altered, and many disappeared in the study because they were awake and vulnerable when they should have been asleep.

Circadian rhythms work for all kinds of organisms, such as keeping these nocturnal animals from leaving their shelter during the daytime, where they would be exposed to more predators and be more vulnerable. It also works for plants and flowers, knowing when to open and close.

In people, circadian rhythms are responsible for coordinating mental and physical systems throughout the body, such as the digestive system producing proteins to match meal timings, while the endocrine system regulates hormones to suit energy levels.

Circadian rhythms are dictated by a master clock in the brain, which coordinates all biological clocks, keeping them all in sync. It is made up of around 20,000 nerve cells to create a structure called the suprachiasmatic nucleus of SCN, so when this was removed in the chipmunk study, this caused chaos for these biological clocks, causing them to become vulnerable.

The SCN is also part of the brain called the hypothalamus and receives direct input from the eyes. This clock in the SCN sends signals during the day to regulate activity throughout the body, and at night when dark and going to sleep, it tells the body to produce melatonin (which induces sleep).

This is also why circadian rhythms are closely connected to day and night. However, there are other cues like exercise, social activity, and body temperature which can influence circadian rhythms. Pretty cool, right??

What Is A Biological Clock?

Circadian rhythms are a type of biological rhythm. There are many different types of biological rhythms, such as infradian rhythm, which explains the menstrual cycle, and ultradian rhythm, which occurs multiple times during the day, such as the sleep cycle.

So while circadian rhythms occur over a 24 hour period, infradian rhythms can occur once every month or every year. Seasonal Affective Disorder (SAD) is another example of a biological rhythm as it is triggered when daylight hours are shorter in winter, causing a knock-on effect on serotonin levels.

Ultradian rhythms can occur multiple times throughout a set period, such as the stages of sleep, which are characterized by different brainwave activities. It’s quite cool how the brain works, don’t you think?

How Does Circadian Rhythm Affect Sleep?

The most well-known circadian rhythm is the one that affects sleep. The sleep-wake cycle is the most important circadian clock you need to know about; it explains why we feel awake during the day and fall asleep at night.

Circadian rhythms are affected by exogenous zeitgebers, which are external factors like lightness that influence our sleep/wake cycle. Light exposure causes our master clock to send signals that generate alertness and help us stay awake and active during the day.

Whereas darkness at night causes the master clock to produce melatonin, which is a hormone that induces sleep. Darkness also helps to keep transmitting signals that help us stay asleep throughout the night.

What Else Does Circadian Rhythm Affect?

Circadian Rhythms affect more than just the sleep-wake cycle; these 24-hour internal clocks play a vital role in pretty much every part of your body, such as your metabolism, mental health, immune system, and much more.

Research suggests that circadian rhythms also affect things like weight and metabolism through the regulation of blood sugar and cholesterol. Circadian Rhythms can also influence mental health as well as the risk of psychiatric illnesses like depression or bipolar as well as neurodegenerative diseases like dementia.

Your circadian rhythm doesn’t just affect sleep disorders and how well you fall aslepe, but it can also influence your immune system as well as processes of DNA repair, which are responsible for preventing cancer. Circadian cycles can influence the effectiveness of anti-cancer drugs– pretty cool, right?

New research and medications may even be able to harness biological clocks to kill cancer cells too!

back sleeper

 What Happens When Your Circadian Rhythm Is Off?

When your circadian rhythm is thrown off, your body cannot function optimally. It causes a rise in serious sleeping problems. Without the proper signaling from your body’s internal clock, it can cause you to struggle to fall asleep, cause you to wake up during the night, and affect sleep in general.

With these sleep disorders, it can also mean that sleep is shallower, fragmented, and offers lower-quality sleep, which opens up a whole new set of problems. Circadian rhythm disruptions can also cause obstructive sleep apnea, which causes lapses in breathing throughout the night.

Obstructive sleep apnea is a sleep disorder that reduces your body’s oxygen levels which can cause numerous sleep interruptions throughout the night. But here are a few circadian rhythm sleep disorders that can be caused when this rhythm is off.

 What Controls Circadian Rhythm?

There are a few things and circadian rhythm sleep disorders that can disrupt the body produce circadian rhythms. Some of these disruptions can be short-term, while others can be long-term. This depends on the characteristics and causes.

Delayed Sleep Phase Disorder:

The delayed sleep phase disorder is when you go to sleep and wake up more than two hours later than what is typically considered a normal sleep-wake cycle. If you have this sleep disorder, then you may also be referred to as a “night owl” as you cannot fall asleep until 2 am or later, but you can sleep well into the afternoon.

If you suffer from delayed sleep phase disorder, then you might be most alert, productive, and creative at night. If you wake up early, your body may feel sleepy during the day, and as a result, you might be perceived as lazy, unmotivated, or a poor performer. This disorder is often found in young adults, typically school and college students.

Advanced Sleep Phase Disorder:

If you have this sleep disorder, then you are more likely to fall asleep early on in the evening (usually between 6-9 pm) and wake up super early in the morning, such as 2 am to 5 am. Those that have advanced sleep phase disorder also tend to suffer from insomnia and tend to feel tired in the afternoon.

It is most common in middle-aged and older adults and can tend to run through the family.

Jet Lag:

Almost everyone has suffered from jet lag at least one stage in their life, especially if you have traveled from one side of the US to the other or outside the US where timezones differ. Because of social cues because the timezone difference, our body is forced to fall asleep earlier/later than usual.

Eastward travel is far more difficult than westward travel because it is much easier to delay sleep than advance sleep. But jet lag not only affects your sleep cycle, but it throws off all your circadian rhythms throughout the day, so you may notice a change in appetite, too, as you may need to eat earlier or later.

The best way to help combat these circadian rhythm disorders is to try your best to fall into the new time zone you are in, such as going to sleep earlier or trying to stay up later than usual. It is far easier to stay up later as when you wake up, your body will start to get used to the time zone better, and you’ll feel more rested.

Shift Work Disorder:

Many shift workers struggle as if you frequently rotate shifts between working in the day or at night. This can conflict with your body’s circadian rhythm, making it difficult for your body to adjust to the changes. This is why many employers are advised to change shifts every 2-4 weeks to prevent this disruption.

Shift work disorder is identified by a constant or recurrent pattern of sleep interruption, which can result in insomnia or excessive sleepiness. It can affect your mood, can cause decreased sex drive and ongoing tiredness.

Non-24 Hour Sleep-Wake Disorder:

This occurs primarily in people who are blind because they are not able to receive light-based cues causing this circadian rhythm sleep disorder. Their body still has an internal biological clock but it can alter from as little as a few minutes to a few hours.

There are many studies to support this where researchers will stay in a cave or dark area for a certain number of weeks with no natural light or social cues to see whether their circadian rhythm will change, but each time it only changed by an hour or two.

Irregular Sleep-Wake Rhythm Disorder:

This is the least common and most rare disorder of them all; people with this disorder have no consistent pattern to their sleep and, as a result, may have many naps and short sleeping periods throughout the 24-hour sleep-wake cycle.

Those with dementia or traumatic brain injury tend to suffer from this circadian clock sleep disorder as these conditions tend to limit the proper functioning of the master clock in the hypothalamus, causing the circadian rhythms to be off and hence causing circadian rhythm sleep disorders.

There are many causes of circadian rhythm sleep disorders; some are related to individual behaviors like traveling or working different shifts, causing our circadian rhythms to be out of whack, while others are caused by underlying issues which cause the inability to receive or process environmental cues.

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How To Fix Circadian Rhythm:

There are a few ways you can maintain a healthy circadian rhythm cycle, and with these healthy sleep tips, you won’t need to use any sleep medicine to help improve your sleep pattern. These tips focus on your body’s natural circadian rhythm and promote the natural cycle.

Sun exposure is always best for promoting the natural cycle of natural circadian rhythm cycle, especially early on in the day, as it helps reinforce the strongest circadian cue. It tells your body’s clock that it is daytime, and it helps get you out of poor sleep habits, such as sleeping in until the afternoon.

That being said, you should also try to follow a consistent sleep schedule and sleep hygiene. Sleeping at different times and waking up at different times can really detriment your natural sleep schedule and even cause circadian rhythm sleep disorders. So try to fall asleep and wake up at the same time, even on weekends.

There are some serious benefits of reading before bed, it is a brilliant way to help promote the natural flow of your sleep/wake cycle. This is because it reduces stress levels by up to 70% so you can fall asleep much easier. Dimming your lights or just using a book light is recommended to help your body relax and prepare for sleep. 

Knowing how much sleep you need is also important as you can practice sleep hygiene with enough sleep hours so you can fall asleep easily and stay asleep. Getting daily exercise can also help support your internal clock and make it easier to fall asleep at night without any sleep medicine.

You should also try to avoid stimulants like caffeine in the afternoon/evening as while it can help you keep awake when tired during the day, it can actually throw off your natural sleep-wake cycle, causing you to have trouble sleeping at night. So it is best to avoid caffeine afternoon.

Reduce light before going to bed. Artificial light such as blue light from your phone can interfere with your natural circadian rhythm cycle. It is advised by experts that you put down your devices before bedtime so your body can naturally emit melatonin to help induce sleep.

If you’re an afternoon napper, then try to keep your naps short and early on in the afternoon. Late and longer naps can actually push back your bedtime and throw off your sleep schedule, which is not ideal.

Just these few tips can help improve your sleep hygiene which can help promote the natural cycle of circadian rhythms and prevent circadian rhythm disorders. If you have persistent sleeping problems or daytime drowsiness, then it is best to talk to a sleep specialist, according to the national sleep foundation.

They can recommend treatments like bright light therapy, which can help shift the circadian system and reset the body clock and help your body distinguish between light and dark.

good sleep hygiene

Final Thoughts:

So there you have it, your circadian rhythm disorder can change a lot about your quality of sleep and life during the day. If you suffer from circadian rhythm disorders and none of this seems to help, then going to a sleep specialist is recommended.

Keeping a good sleep environment is key, too, as you don’t want to fall asleep in an environment that is too hot. This is because your body temperature needs to drop one degree in order to achieve the deeper sleep stages; your body struggles to do this when the environment is too hot. This includes choosing the right mattress that is not too hot and offers enough comfort and support

So give a few of these tips a go, and remember consistency is key to getting good quality sleep!

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