What is a Circadian Rhythm?

Often referred to as the “internal body clock”, the circadian rhythm influences the timing of all our bodily rhythms, including our sleep-wake rhythm.

The cycle is completed approximately once every 24-hour period, which is why these regular rhythms are called circadian (circa=about, dian=day) rhythms.

Your sleep health and overall well being is dependent on your circadian rhythm working correctly; and remaining synchronized with night and day.

The most important external indicator to help keep your body synchronized with this routine is light.

Why is light important to our circadian rhythm?

When the eye senses light, it sends a signal to your brain to be awake.

As it becomes dark in the evening, your body produces melatonin, (often called the sleep hormone) telling your body it is time to sleep.

The combination of biological processes in response to light and darkness are crucial factors for your body to remain synchronized and sleep at the right time.

If you do not receive light at the right times due to the winter months or lifestyle factors, this can confuse your circadian rhythm leaving you unable to sleep when you need to or contribute to the Winter Blues. Winter Blues is a mild form of low mood experienced during the winter months. 

What can disrupt your circadian rhythm?

Sleeping and waking difficulties can occur when there is a discrepancy between the circadian rhythm and an individuals preferred sleep period.

This can occur for a number of reasons, and can cause a circadian rhythm disorder.

Lifestyle factors

Shift work: working different shifts requires you to adjust your sleep-wake times to accommodate your work life. Often this means having to sleep during the day which is contrary to your body’s natural rhythm, or experiencing fatigue during your shift. Read more about Shift Work here.

Travel: frequent travel may require you to cross multiple time zones. This can disrupt your existing sleep-wake rhythm and result in you feeling jet lagged and unable to sleep. Read more about Jet Lag here.

Seasonality: lack of morning light during the winter can cause you to have trouble sleeping at night and then waking in the morning. This lack of morning light may also contribute to Winter Blues. Read more about Winter Blues here.

Biological factors

A number of people may be affected by a circadian rhythm disorder including:

  • Delayed Sleep Phase (also referred to as sleep onset insomnia): may cause you to have difficulty falling asleep at your desired bedtime. Typically, people are unable to sleep until after midnight and then find it difficult to wake up early in the morning for school or work commitments. 


  • Advanced Sleep Phase (also referred to as early-morning awakening insomnia): may cause you to feel overwhelmingly sleepy during the early evening, essentially rendering you unable to stay awake. Your bed times may be as early as 7pm causing a wake time of around 3am, impacting your work and social life. 


What are the symptoms of a circadian rhythm disorder?

If individuals try to sleep at a time that does not match their circadian rhythm then this can result in the following:

  • Poor sleep quality
  • Insufficient sleep duration
  • Sleepiness and fatigue
  • Impaired overall well-being in family and social life
  • Decreased motor and cognitive performance

How can I adjust my circadian rhythm?

For each of these lifestyle and biological factors, appropriately timed bright light therapy is effective in altering circadian rhythm timing and consequently improving sleep.

See our dedicated pages on how to wear Re-Timer for your situation.

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