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What is a Circadian Rhythm?

What is a Circadian Rhythm?

What is a Circadian Rhythm?

What is a circadian rhythm?

Your circadian rhythm is your 24-hour body clock, the part of your brain that tells you when you’re tired, when you’re alert, and when you’re everything in between. But what does this futuristic sounding body function have to do with humans, and why is it so important? 


As it turns out, your circadian rhythm is an important natural timekeeper - and it massively impacts the way we live. We all have our own unique circadian rhythm meaning we experience a natural, biological cycle of behaviour and physical changes, through both day and night. 


So how does your circadian rhythm work? How does circadian rhythm affect sleep? What can disrupt your circadian rhythm, and what can you do to support it? Read on! 

Where does the phrase ‘circadian rhythm’ come from?

The term ‘circadian’ comes from Latin. Circa means ‘close to’ and diem means ‘day’, and together they relate to the way our bodies take influence from nature. It’s no coincidence that we're attuned to the sun, waking up when it rises and slowing down as it sets.

The science of sleep patterns

Your circadian rhythm is mostly controlled by the hypothalamus in your brain, but it’s also impacted by external signals - namely the light levels outside. At night, your eyes tell your hypothalamus that it’s almost bedtime. That’s when it releases melatonin, the magic chemical that triggers feelings of sleepiness. When it’s light, melatonin levels drop, which is why you’re more alert during the daytime. 


That’s the simple explanation, but if you want to know more, check out this guide to melatonin.

How long is your circadian rhythm?

Our body’s natural cycle lasts a full day, and within this 24-hour period, our physical and mental abilities change. You’ll know from experience that working in the very early morning and late at night is difficult, but have you noticed that at around 3pm, our body faces a decrease in alertness? 


Some blame it on lunch, but according to sleep researcher Christopher M. Barnes, this is a natural dip in your body’s circadian process. The cycle continues into the afternoon, rising and peaking for a second time (the first being at noon) at around 6pm. We then begin the later part in our day, filled with energy until bed. Melatonin production then goes up, we feel tired, and we (hopefully) stay asleep until the morning - when the whole thing starts again. 


A typical Circadian Rhythm, hour by hour:



 What happens

Midnight to 6am

period of the deepest sleep and lowest body temperature

6am to midday

we experience a surge of cortisol (the stress hormone we need to wake up) and increasing blood pressure followed by high alertness

Midday to 6pm

a period of peak coordination and reaction times, increasing blood temperature  

6pm to midnight

highest blood pressure, melatonin (the sleep hormone) secretion


What can disrupt circadian rhythm?

A great example of when your circadian rhythm is instantly affected is jet lag. Jumping through time zones will result in your body feeling several hours out of sync, leading to fatigue, confusion and often sickness.


Shift work is also a cause of upset for the body clock, as it means that a natural rhythm cannot be established. The body fights to keep up with itself, and our immune system is weakened as a result.


The ageing process impacts our body clocks, too. The high energy levels of children early in the day wanes as they grow into teenagers, only to come back during the later stages of life when older people tend to rise much earlier. As adults, our body decides whether we are ‘larks’- early risers - or ‘owls’ who roam at night, otherwise known as our chronotype.

How to reset your circadian rhythm?

So how do you know if your circadian rhythm is off? If you find yourself feeling tired during the day or unable to sleep at night it’s likely that your circadian rhythm needs a reset, and your routine doesn’t match the needs of your internal body clock - which means the solution is lining them up again. 


- Frequent flyers who suffer from jet lag can adapt by embracing the bedtime of the countries they land in, resting in dark, quiet rooms where possible. The body takes a day to adjust to up to two time zones; anything more will take up to five. 


- In general, making the room where you sleep as dark and quiet as possible is important in keeping your circadian rhythm healthy. Alertness drops to a minimum at around 2am, so making sure you feel safe and comfortable during sleep is vital.


Whatever the reason for your disrupted sleep schedule, good sleep hygiene is the best way to solve your problems and get your rhythm back on track.


How to maintain a healthy circadian rhythm

Supporting your natural body clock is as easy as sticking to a realistic and healthy routine (that means no all-nighters, students!). We know it’s easier said than done, but if you can follow these general guidelines, you’ll be in for a much better night - and day.


- Set a bedtime

to help you get into a healthy routine. If your body and brain get used to having the lights out at a certain time, you’re more likely to start feeling tired in anticipation.

- Make yourself comfortable to ensure an undisturbed night.

Get the room to a good temperature, make sure you have everything you need, and - of course - invest in a quality mattress that helps you sleep, if you can.

- Ditch the screens 

Blue light from electronic devices can play havoc with your sleep pattern. Here’s why.

- Reduce your stress levels during the day

Easier said than done, we know, but by identifying what’s making us unhappy - and tackling it - we’re doing a huge favour to our body’s ability to sleep when we’re tired.

- Do some exercise

Getting some exercise in during the day, or if you can stretch right before bed, it can help you feel tired when you hit the pillow.


Changes to your circadian rhythm

Did you know what our circadian rhythm changes as we age? Everyone is different, but as we age, it can be increasingly harder to sleep. Despite the common misconception, it’s not because we need less sleep. We’re simply more likely to wake at night due to discomfort, hormonal changes, or needing to do things like use the bathroom. This in turn can have a knock-on effect on our rhythms, leaving us feeling more tired.


The important thing is simply to look after ourselves, notice and accept changes, and do what we can to ensure we get a good night’s sleep as far as possible.


All in all, the more time we spend developing great sleep hygiene, the better we’re sleep - and the better we’ll feel!

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