Circadian Rhythms: What Are They, How do They Work, And How do They Affect Sleep?

You’ve probably heard about circadian rhythms, but what exactly are they, how do they work, and how do they affect our sleep?

In this post, we’ll dive into the science of these mysterious bodily processes and explain their impact on our sleep-wake cycle.

What are Circadian Rhythms?

What Are Circadian Rhythms

Circadian rhythms are a set of internal processes which follow a 24-hour cycle, keeping our bodies functioning as they should.

Everyone has their own circadian rhythms, and it’s not just humans; most animals, plants, and even fungi have them too.

These internal rhythms run along in the background, regulating the body’s essential functions and processes, including our sleep-wake patterns.

And so, they play a crucial role in our health. When our circadian rhythms are properly aligned, our sleep schedule is consistent, and the quality of our slumber is optimized. But when they’re thrown off kilter, sleep problems like insomnia can occur.

However, that’s not all. An imbalance in the circadian rhythm has also been linked to mental health disorders such as depression and anxiety and physical health problems, such as cardiovascular disease, diabetes, and cancer.

How do Circadian Rhythms Work?

Circadian rhythms are responsible for regulating our sleep-wake cycles, but how do they do it?

Before we dive into the details, we need to understand two other closely linked internal systems; our biological clocks and our master clock.

1. Biological Clocks

Biological clocks

Biological clocks are internal timekeepers composed of protein molecules that communicate with our cells to regulate our circadian rhythms. Almost all of our organs and tissues have their own biological clocks, which keep them functioning as they should.

2. The Master Clock

The Master Clock

As its name suggests, our master clocks are responsible for regulating the biological clocks in the body and keeping them running in sync.

For humans, the master clock is made up of around 20,000 nerve cells, or neurons, which together form the suprachiasmatic nucleus or the SCN.

The SCN is located in the hypothalamus, the area of the brain responsible for the body’s endocrine system, where critical hormones are released.

The SCN, and in turn, the master clock, is triggered by light. It responds to these triggers by coordinating the body’s various biological clocks by releasing or suppressing certain hormones to create a physiological response.

3. Biological Clocks And Circadian Rhythms; What’s The Difference?

These terms are often used interchangeably, but some key distinctions exist between them.

Biological clocks are composed of various molecules that communicate with cells, forming the body’s built-in timing devices.

And circadian rhythms are the physiological and psychological changes that happen in response to our biological clocks.

They each run on a 24-hour cycle which is innately tuned to the natural world.

Circadian Rhythms And Sleep

Circadian Rhythms And Sleep

Our circadian rhythms play a vital role in multiple bodily functions, including our core temperature, hunger levels, digestion, and the release of certain hormones.

But the most profound and noticeable effects of circadian rhythms are found in the regulation of sleep.

Light and dark perceived by the optic nerve send signals to the brain via the SCN or the master clock. This then triggers our biological clocks to release hormones that tell our bodies when it’s time to wake up and when it’s time to drift off to sleep.

When we are in darkness for an extended period of time, the endocrine system secretes the sleep hormone melatonin, making us feel drowsy and ready for bed. But when our eyes are exposed to light signals again, melatonin is suppressed.

Once the sun rises and we’re back in a wakeful state, our biological clock signals the body to release cortisol. This cortisol in our body sustains our energy levels and keeps us going throughout the day.

And when the sun sets in the evening and the light levels fall, the cycle begins again.

What Factors Affect Circadian Rhythm?

As we have discussed above in brief, Circadian Rhythm and how it affects, let’s get into the detail of what are the factors that affect them. It is essential to have a complete understanding of the Circadian Rhythm.

1. Light


As we’ve seen above, light is the most crucial external factor that controls our circadian rhythms.

Before the days of electricity, humans were exposed to light in the earth’s natural 24-hour cycle. Our bodies are designed to work in synchronicity with these cycles, which is why most people tend to feel sleepy when it gets dark and awake and energized in the light of day.

But in the modern world, most of us spend time in an artificially illuminated environment for several hours after the sun goes down, and this irregularly timed light can confuse our naturally attuned circadian rhythms.

This has a profound effect on our sleep patterns. Our circadian rhythms enter their most sensitive phase around two hours before we’re due to fall asleep, and they stay in this phase throughout the night until about an hour before we wake up in the morning.

2. Light Wavelengths And Color

Light is the strongest driving force of our circadian rhythms, but different light wavelengths have different effects.

Light wavelengths are the reason that we perceive color in the way that we do; after all, colors are simply electromagnetic radiations with varying wavelengths. So, color plays a crucial role in our circadian rhythms, too.

1. Blue Light Waves

Blue Light Waves

Blue light has the shortest wavelength on the color spectrum, and it also has the strongest impact on our circadian rhythms.

Unfortunately, in our modern society, we’re increasingly exposed to blue light at unnatural intervals throughout the day.

Certain types of LED bulbs and devices, such as laptops, tablets, and cell phones, all emit blue light. And when our eyes detect this light in the hours leading up to bedtime, our circadian rhythms become misaligned, and falling asleep becomes more difficult.

2. White Light Waves

White Light Waves

White light also contains blue light; in fact, white light is a combination of all the wavelengths of the visible color spectrum.

The sun is the greatest natural source of white light, and exposure to sunlight during the day has positive effects on our circadian rhythms, making us feel more alert, awake, and energized.

Artificial sources of white light include white LEDs and fluorescent bulbs, and while these are fine before sunset when our eyes detect this type of light during the natural hours of darkness, it can wreak havoc with our circadian rhythms.

3. Warm Color Light Waves

While color wavelengths on the cooler side of the spectrum, such as blue and white light, confuse our circadian rhythms after sunset, that’s not the case for warmer wavelengths.

Colors on the warmer end of the chromatic spectrum, such as yellow, orange, and red, are gentler and don’t disrupt the production of that all-important sleep hormone, melatonin.

These colors have longer wavelengths, and since they mimic the sunset, they tap into the body’s innate evolutionary circadian rhythms, triggering the physiological processes that induce sleep.

So, exposure to these types of light before bedtime can actually have a beneficial effect.

But you don’t need to stare at the sunset each night to rebalance your circadian rhythms (although if you can, you should!). Incandescent light bulbs are a common source of artificial yellow, orange and red light, so switching to these can help a lot.

Red light is particularly beneficial for your circadian rhythms and, in turn, your sleep patterns. To counteract the negative effects of cool light exposure in the evenings, consider investing in a red spectrum bulb for your nightstand and watch how your sleep improves.

How to Rebalance Circadian Rhythms For a Better Nights Sleep?

If your circadian rhythms are out of balance and you’re struggling to drift off at night, it’s time to recalibrate.

Here are a few tips to reset your body’s innate natural cycles for a better night’s sleep.

1. Set a Sleep Routine

Set a Sleep Routine

Try to go to bed and get up at the same time each day. Keeping a structured sleep routine helps your circadian rhythms regulate themselves and produce the right hormones when you need them, helping you gear down for sleep and wake up feeling energized and refreshed.

2. Limit Light Exposure

Limit Light Exposure

Since light is the key driving force behind our circadian rhythms, exposure to certain types of light at the wrong time can disrupt the delicate balance of our sleep cycle.

So, try to avoid using blue light-emitting devices, such as your cell phone, for at least an hour before you go to bed. Also, consider switching white LED and fluorescent light bulbs to incandescent bulbs or red spectrum bulbs.

These will be much gentler on your eyes in the evening, helping you to rebalance your circadian rhythms and fall asleep when you should.

3. Avoid Exercising Late at Night

Avoid Exercising Late at Night

Exercise is a great way to help you sleep, but it’s best done during the daytime when you can use the boost of energy it provides to your advantage.

Hitting the gym in the evening can throw your circadian rhythms off-kilter and delay the release of melatonin, leaving you feeling wired and energized way past bedtime.

4. Avoid Caffeine Later in The Day

Avoid Caffeine Later in The Day

Stimulants like caffeine stay in your system for several hours, and if you consume them later in the day, they can have a negative impact on your circadian rhythms and prevent you from feeling drowsy enough to fall asleep.

So, try to drink your last cup of coffee in the early afternoon, and then switch to caffeine-free herbal teas instead.

5. Talk to Your Doctor

Talk to Your Doctor

If you’re concerned that your circadian rhythms are out of balance and affecting your quality of sleep, then it’s best to speak to your doctor.

In the long term, a disrupted circadian rhythm and a chronic lack of sleep can lead to severe physical and mental health problems, so it’s important to address the issue and get your body back on track.

In some cases, your doctor may prescribe a course of melatonin supplements, which, when used correctly, can help to reset your internal clock and get your circadian rhythms back in balance, resulting in a better night’s rest.


Circadian rhythms are innate evolutionary processes that are finely tuned to the rhythms of nature. But in our modern world, they can easily become disrupted, and our sleep cycles can suffer as a result.

So, if you’re struggling to drift off at night, or get out of bed in the morning, then it might be time to check in and recalibrate your circadian rhythms.

For more tips on how to work with your body’s natural processes and improve your bedtime routine, take a look at our in-depth guides to tweak your sleep environment. A few minor changes can help to rebalance your circadian rhythms and transform the way you sleep.

Sarah Wagner

I'm Sarah Wagner, and I founded Sweet Island Dreams in 2022. It's a blog dedicated to helping people mental vacation virtually anytime they want. By providing information about the best sleep of your life, I help people drift away to paradise without ever having to leave their bed!