Applied Psychology

How the circadian rhythm affects your sleep cycle

Jul 13, 2018

The term ‘chained to the rhythm’ has new meaning when evaluating the impact of the circadian rhythm on the sleep cycle.

Key takeaways:

  • All living beings are governed by a built-in rhythm known as the circadian rhythm.
  • One of the main roles of the circadian rhythm is to regulate sleep.
  • The amount of time it takes for a person to go through all five sleep phases is known as a sleep cycle.
  • Disruptions in the circadian rhythm can result in disruptions in the sleep cycle.
  • The circadian rhythm plays a direct role in determining whether a person is an early bird or a night owl.

Studies have shown that the circadian rhythm has a direct impact on your sleep cycle and that irregularities in the rhythm can have an impact on your mental health.

What is the circadian rhythm?

Have you noticed that you usually feel sleepy around the same times every day? Do you find yourself craving a post-lunch nap? This is a direct result of your circadian rhythm.

Plants, animals and humans are governed by a built-in rhythm or pattern known as the circadian rhythm. The circadian rhythm plays a pivotal role in a number of biological functions, such as body temperature and brainwave activity. Most importantly, in terms of the sleep cycle, the circadian rhythm plays a vital role in the production of melatonin the hormone that helps your body know when to sleep and when to wake up. As a result, one of the main functions of the circadian rhythm is regulating when you feel alert or sleepy.

Your circadian rhythm is controlled by the hypothalamus. It does not work alone however, the rhythm is assisted by external cues known as zeitgebers. When it comes to sleep the most important zeitgeber is the light and dark cycle. In simple terms, this works as follows: when it is dark your eyes send a signal to the hypothalamus telling it that it’s time to feel tired. This is followed by your brain sending a signal to your body resulting in the release of melatonin which, in turn, makes your body tired. As a result the circadian rhythm generally coincides with the day-night cycle. This explains why shift workers often find it difficult to stay awake at night and sleep during the day.

The circadian rhythm also plays a direct role in determining whether a person is an early bird or a night owl. According to research natural variances in the circadian rhythm result in sleep session biases meaning that we fall into one of three categories: morning people known as larks, evening people or owls, and those who fall in between. According to research, the majority of people fall into the intermediate range, with only 17% of the population being owls and 1% being larks.

What is a sleep cycle?

There are traditionally five stages of sleep, the last being rapid eye movement (REM) sleep. The process occurs cyclically, starting with phase one and ending with REM and then back to phase one. A sleep cycle is simply the amount of time it takes for an individual to pass through all five stages of sleep. Research indicates that the first sleep cycle of the night is generally 90 minutes followed by cycles of 100 to 120 minutes. On average we go through four to five cycles each night.

How does the circadian rhythm affect your sleep cycle?

The sleep cycle is the result of an interaction between the circadian rhythm and the sleep-wake homeostatic process. The sleep-wake homeostasis works as an internal timer that generates a homeostatic sleep drive, which is based on the amount of sleep you have had in the past and your current sleep deficit. The sleep drive is very similar to the hunger drive. If you haven’t eaten all day, you will be hungry whether it is mealtime or not. If you had a big breakfast however, chances are that you won’t be very hungry at lunch. Similarly, if you didn’t sleep all night you’re likely to feel sleepy the following day even if the sun is shining.

Disruptions in the circadian rhythm can result in disruptions in the sleep cycle. Jet lag is an excellent example of this. Travelling through different time zones and day-night cycles can result in our circadian clock becoming out of sync. This interruption in rhythm and the need to reset causes jet lag. As the body clock adjusts to the new time zones the jet lag eases. The severity of the jet lag is directly linked to the number of time zones crossed.

Circadian rhythm and sleep hygiene

Getting the right amount of sleep is extremely important for good mental health. Sleep hygiene, like dental or personal hygiene, is a set of daily practices or habits that we keep to promote our own health and wellbeing. Going to sleep at odd times, or not getting enough sleep in the long-term, can interfere with your circadian rhythm causing issues such as fatigue, struggling to fall asleep or waking up at the wrong times. Having good sleep hygiene promotes more restful sleep which boosts energy and alertness during the day, improves general mood and lowers the risk heart disease, stroke, diabetes and dementia.

It is up to everyone to develop sleep hygiene practices that work for them. Some good starting points are: limit day time naps to 25 – 30 minutes, cut out caffeine later on in the day, avoid eating too late in the evening and give yourself a break from screens and other harsh light sources an hour before sleeping. Check out some night time backlighting apps for your phone if you find that you can’t put it away!

Research shows that the circadian rhythm directly impacts sleep patterns and the overall sleep cycle. So if you’re struggling to sleep or battling to wake up, it might be time to rediscover your rhythm.

Study psychology at SACAP to find out more about the connection between human biology and the inner workings of the mind. Courses such as the Bachelor of Psychology degree and the Bachelor of Applied Social Science can pave the way for a career in psychology, while providing you with invaluable knowledge and skills that will serve you well in life. For more information, enquire now.

Previous post

Next post