Our circadian rhythm is our internal clock, and understanding it can help ensure a better night’s sleep.
Learn more about what our circadian rhythm is, how it works and, importantly, how it affects the quality of our sleep.
What is our circadian rhythm?
Our circadian rhythm is our internal clock, which tells our bodies when to do things, like eat and sleep.
How does our circadian rhythm work?
Our exposure to sunlight is the main way that we control our circadian rhythm. Our eyes not only process what we see in our visual cortex, in the brain, but there is also a separate neural pathway to our suprachiasmatic nucleus (SCN), whose sole job is to monitor light levels.
When your eyes see the maximum brightness of light (or lux) of the day, then your brain flags this as midday, and our 24-hour circadian rhythm clock is anchored around that point.
If your maximum sunlight exposure of the day is when you go home from work at 5pm, instead of at lunchtime (i.e. because you did not leave the office), then your circadian rhythm may want you to go to bed later and wake up later than you would like, as it thinks that 5pm was actually midday.
How does the circadian rhythm affect sleep?
Your circadian rhythm is responsible for producing a hormone called melatonin. This hormone regulates sleep. We naturally produce melatonin to help us go to sleep, around 8 to 10 hours after our maximum sunlight exposure of the day (see above).
If we try to sleep when our circadian rhythm thinks it is daytime, it can be very difficult to sleep. You may have experienced this when you have travelled to another country (commonly known as ‘jetlag’) because your body’s circadian rhythm is on another time zone.
Why is our circadian rhythm important to physical and mental health?
Our circadian rhythm not only controls sleep, but it also controls a whole host of other things, including when we produce hormones and when we produce digestive enzymes, to make us hungry.
Our circadian rhythm also makes us produce cortisol in the morning, which helps us wake up and helps us to feel alert.
What impacts our circadian rhythm?
As already mentioned, sunshine exposure is the main regulator of our circadian rhythm. We also get cues from when we are physically active and when we eat. If you skip breakfast, for example, then your circadian rhythm won’t know that it is actually morning yet. Also, if you eat food in the middle of the night, then your circadian rhythm can think it is already morning and start to regularly wake you up too early.
Electronic devices that emit light, such as phones, tablets, laptops and computers, can emit a bright blue frequency of light which our brains interpret as bright daytime sunshine. If you are looking at screens late in the evening, then your eyes will be exposed to this blue light and your circadian rhythm will think that it is much earlier in the day and try to stop producing melatonin. This means you won’t feel sleepy and can disrupt falling asleep.
How can we tell if our circadian rhythm is ‘out of sync’?
It can be very obvious. For example, our circadian rhythm can be thrown off when we are working shifts, or if we have been on holiday in a different time zone. You may feel sleepy, even though it is mid-morning, and feel wide-awake in the middle of the night.
It can also be more subtle. You can experience problems with your circadian rhythm if you go to bed late and sleep in at the weekend. You may then struggle to go to sleep early on Sunday night, in order to get up on time on Monday morning.
If you are finding yourself getting very sleepy too early or not feeling tired when you want to go to bed, it may be a sign that your circadian rhythm is not in the ‘right time zone’ for you and your lifestyle.
Is everyone’s circadian rhythm different?
There are many individual variations in our circadian rhythm – this is a personality trait popularly referred to “larks and owls”.
Larks are people who tend to go to bed early and get up early, whereas owls are those who prefer to go to bed late and sleep in late in the morning.
If you are a lark, then you are likely to feel more alert early in the day and it is a good idea to schedule your day so that you can address difficult tasks in the morning. Owls, on the other hand, may not feel fully awake first thing in the morning and would be better to delay the more taxing chores of the day until later.
What can we do to maintain a healthy circadian rhythm to help us sleep better?
Finally, here are three important habits to help you sleep and maintain a healthy circadian rhythm:
Tip 1 – Get outside every day
It is really, really important to make sure that you get outside every day to get some natural daylight. It is too easy to get up, log onto your computer, and spend all day inside never seeing the Sun. This can lead to a weak circadian rhythm or, even worse, a circadian rhythm that thinks it is in a different time zone.
Tip 2 – Eat regular meals
Eating meals at regular times throughout the day and making sure that you get some exercise each day will also help your body to know the difference between day time and night time.
Tip 3 – Avoid screens at bedtime
Avoiding screens near to your usual bedtime will help avoid the blue light disruption, but if you must use screens then make sure you have enabled night mode on your device, to automatically take out the blue light in the evening.