circadian rhythm

The circadian rhythm – everything you need to know

Are you a natural ‘morning person’, or do you love a lie-in? Do you thrive on six hours’ sleep, or are you a nine-hours-a-night type?

Have you noticed this changing over the years, or have you had a similar sleep pattern for as long as you can remember?

The answers may lie in more than just your lifestyle habits. Meet your circadian rhythm.

What is the circadian rhythm?

Humans, like all living things, have a circadian rhythm. The circadian rhythm is the brain’s way of aligning the body with the environment. In simple terms – it’s your body’s built-in clock.

As any cat owner will attest to - felines have a circadian rhythm to suit their nocturnal hunting habits and are most active between dusk and dawn.

In humans, the circadian rhythm is a 24-hour sleep/ wake pattern set by a light-sensitive inner body clock. We sleep when it’s dark and are awake and alert when it’s light.

Our ancestors once lived by their circadian rhythm – getting up with the sun and going to sleep when darkness fell. In modern times, however, electric lighting, technology, alarms and commuting times mean that many of us are keeping hours which might be at odds with our natural body clocks.

What controls the circadian rhythm?

Your circadian rhythm is controlled by a small area within the section at the base of your brain called the hypothalamus.1

The hypothalamus instructs the body to release certain chemicals and hormones during each 24-hour period. The timing of these releases is in-built into our body clocks - but they’re also partly influenced by external factors.

These external factors include whether it’s light or dark. The hypothalamus receives signals from the eyes when it’s dark, causing it to release melatonin – the sleep hormone – which makes you feel tired.

Light stimulates the production of cortisol – which wakes your body up and energises you for the day ahead.2

Why is the circadian rhythm important?

The circadian rhythm sets the pace for the body’s rest and repair.

Deep sleep is vital for cell regeneration. So, whenever you’re catching good quality sleep, your body is using that time to restore itself.3

Your immune system, cardiovascular system and muscles are all areas which undergo this restorative process as you sleep.

How do circadian rhythms differ?

Just like people, no two circadian rhythms are exactly the same. Circadian rhythms can also change throughout our lives.

  • After birth, babies typically take a little time to adjust to the light/ dark circadian rhythm. At first, babies sleep between 12 – 16 hours of sleep in a 24-hour period, including naps. This reflects the huge amount of growth that is occurring in their bodies. Young children up to age five are beginning to synchronise with the light/ dark circadian rhythm, and should get between 10 – 14 hours, including naps.
  • Teenagers need around between 8 – 10 hours of sleep.4 Teens have a developing circadian system, so they can find early starts challenging. (This isn’t just a myth!).5
  • Adults over 60 can find themselves tired earlier in the evening than when they were younger. Older adults also wake up more during the night and tend to wake up early in the morning.6

What can disrupt the circadian rhythm?

A major factor which disrupts the circadian rhythm is unnatural light. This could be electric lights in the house, a streetlight outside your bedroom window, or the glare of a TV, mobile phone or other electronic device.

The blue light which comes from electronic devices can suppress melatonin production, which can stop you feeling tired and making it more difficult to drop off to sleep at night.7 Shift work is another significant disruptor of the circadian rhythm. Irregular work schedules which include night shifts (such as those undertaken by healthcare workers) can lead to insomnia and/or excessive sleepiness. This phenomenon has even been called shift work disorder (SWD) by scientists.8

How can I improve my circadian rhythm?

The best thing you can do for your circadian rhythm is to give it routine and predictability.

  • Go to bed same time each night. As anyone who has ever stayed awake until dawn to finish a box set will know, irritability and lack of focus often follow the next day, even if you catch up on the sleep with a lie-in. So, it’s vital to establish a bedtime which is roughly the same, whether that’s 10pm or 1am.

  • Exercise during the day. Physical activity can help improve sleep quality, helping you feel less drowsy in the day and drop off easier at night.9 Also, the natural daylight you get by being outside helps synchronise your circadian rhythm to the light/ dark pattern.

  • No phones in the bedroom! This is a difficult one, but the blue light that screens emit is a major sleep disruptor. If you can’t stick to a no-phones rule, then make sure they’re on night mode and across the room from the bed. 

  • Don’t go to sleep with the TV on. It may feel soothing to have a little background noise, but it’s stopping you from entering the deep restorative sleep you need. If you struggle to sleep in silence get a white noise machine or sound box. 

  • Do you often find yourself working late? Block blue light using a blue light filter on your laptop. You can also buy blue light-blocking glasses. Also, remember to glance away from your laptop screen frequently to avoid eye strain. 

Last updated: 26 May 2020

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