What is the Circadian Rhythm and how does it affect our sleep?

25 May, 2011

The circadian rhythm is a (roughly) 24-hour cycle in the chemical, physical and mental processes which go on in the human body.

Appearing in most living things, circadean rhythms are directed by genes which have been identified in fruit flies, mice and fungi as well as humans.

Circadian rhythms are driven by the body’s biological clock, groupings of interacting molecules in cells throughout the body.  These biological clocks are in turn controlled by a master clock in the brain which keeps all the body clocks in sync.

External cues (daylight in particular) also influence the circadian rhythm.  Deprived of sunlight, our biological clocks would naturally work on a 25-hour cycle.  But sunlight resets our master clock to a 24-hour cycle, coordinating our bodies with the natural rhythms of nature.

In an ingenious example of synchronicity with the world around us, the circadian rhythm allowed our ancestors to adjust to precise changes in their environment, such as the availability of food during autumn and winter.   It is also critical in the sleep-wake cycle.

The body’s master clock is positioned just above the optic nerve, which relays information from the eyes to the brain.  So the master clock receives information about incoming light and uses that information to control the pineal gland’s production of melatonin, a hormone that makes you sleepy.

When there is less light (at night), the body clock tells the pineal gland to produce more melatonin and you feel ready for sleep.  During the day, when an increasing amount of light is detected by the retina, melatonin production is reduced and you feel more awake.

An individual’s circadian “clock” also determines the best time for restorative sleep.  So any disruption of the circadian rhythm, such as lack of exposure to daylight, will disturb our sleep cycle and affect our quality of sleep.

Sometimes, it is possible that your routine is at odds with your circadian rhythm.  Shift workers or those who travel across international timelines and suffer jetlag as a result are examples of those whose daily schedule is out of sync with natural sleep-wake cycles.

There are some simple techniques which can be used to reset your master clock if you fall into this group:

  1. Slowly adjust your bedtime to fit in with your schedule
  2. Keep to regular sleep schedule.  Do not, for instance, sleep in at weekends
  3. During ideal sleep time, ensure that your room is completely dark
  4. Use light therapy at appropriate time to inhibit production of melatonin and make you feel more awake
  5. If traveling across time zones, adjust your clock to the new time zone as soon as possible after you leave, and give yourself time at your destination to acclimatize to the new time zone.

Different individuals may have a tendency to feel more awake at different times of day due to the individual natures of their body clocks.  We can loosely divide ourselves into early birds or night owls.

According to The Daily Mail, women’s circadian rhythms run six minutes faster than men’s, making them much more likely to be early birds than night owls.  It also means that women are more likely to need to go to bed earlier.

Circadian rhythms are just one elegant example of the cycles which affect the way in which our bodies and minds operate.  Others include seasonal, tidal, lunar, and annual cycles.

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