Commonly known as the ’body clock’, the circadian rhythm is an innate cyclical rhythm that regulates many bodily functions automatically throughout the day, and does not require conscious control.
There are those that are apparent to us, such as the sleep-wake cycle and the digestive cycle, for which we feel sleepy or hungry when we reach a certain time of the day. There are also those that are not so obvious such as core body temperature and the release of hormones into the bloodstream.
In human beings, this innate rhythm cycles between the duration of 24.2 to 24.9 hours, just slightly longer than a day. This could potentially create a messy situation where we could fall asleep or need to eat at very inconvenient timings, over a period of time.
Fortunately, this ’clock’ is synchronised to the 24-hour day by environmental inputs, most importantly by sunlight, as well as by social rhythm such as common meal times, work schedules, and physical exercises.
Genetics largely influence the variations between individuals, hence there are people whom we recognise as ’larks’ (preferring to sleep early in the night) and ’night owls’ (ability to stay up late into the night).
Genetics also determines the ability of individuals to adapt to time cues in the daily cycle, and hence the ability to ’tune their clocks’.
With age, this innate rhythm can also change in its cycle length, commonly reflected through changes in sleep pattern as one grows older.
Problems with Circadian Rhythm
It is important that you keep to
a regular sleep schedule, as this
maintains synchrony of the ‘body
clock’ with the demands of social
activities and duties. Any situation that
desynchronises the circadian rhythm
and the social rhythm will result in
sleep difficulties as well as problems in
The most common causes of disruption
to circadian rhythm are jet lag, shift
work and circadian rhythm disorders.
1. Jet Lag
This is a transient condition in which the circadian rhythm is temporarily out of synchronisation with the external environment when a person travels across several time zones rapidly.
The symptoms are usually daytime fatigue and sleepiness, insomnia, stomach upsets, moodiness and feeling of unsteadiness. Some may also experience chills, and others have episodes of feeling hot and sweaty.
As our body clock runs slightly longer than 24 hours, jet lag is worse when we travel eastwards than when we travel westwards. It is easier to lengthen the day (delaying going to bed) than to shorten it (trying to fall sleep earlier). After travelling from east to west, early waking is the main problem, as oppose to difficulty falling asleep when travelling from west to east.
Our circadian rhythm will eventually synchronise with the local time at the destination, at a rate of roughly one day per hour of time difference.
Tips for managing jet lag:
- If you are able to, choose a destination that involves flying westwards.
- Choose daytime flights to avoid losing sleep.
- Use sleeping aids such as blindfolds, earplugs, and neckrests to help you sleep during the flight.
- Adjust to local time by keeping to local routines at your destination, such as taking meals when the locals do.
- Try to keep awake during daytime. Staying in a brightly lit environment will facilitate the adjustment of the body clock.
- If necessary, naps should be short, and planned so as not to affect night time sleep.
- Melatonin supplement may be helpful for jet lag symptoms and improving sleep when taken near bedtime.
- Exercise during the day.
- Caffeine may help in maintaining alertness.
- Plan ahead for your journey and make allowances for adjustments where possible.
2. Shift Work
Shift workers are people who work
non-traditional hours, which may be exclusively at night, or on rotating
shifts. They often face problems similar
to jet lag, even without crossing time
zones. The differences between their
‘day’ during which they are working,
and the natural day-night cycle have
resulted in a desynchronised circadian
rhythm. While some may have no
problems adapting to this demand,
many suffer from sleep problems.
They may experience insomnia, and
may not get enough sleep during
the day as the brain remains active,
culminating in sleep deprivation.
This eventually leads to wake time
sleepiness and impaired work
performance. They may have sleep
problems even on their days off.
The main objective of managing
shift work sleep problems is to try to
resynchronise the circadian rhythm
to the work schedule as quickly as
possible. In addition, we try to improve on the quality and duration of sleep
at bedtime to reduce effects of sleep
deprivation. This is typically easier to
achieve for people who work regular
shift, and treatment is similar to that for
jet lag which is to adjust the body clock
to a new ‘daytime’.
What if I work rotating shifts?
The day before night shift: Get up
at your usual time and have meals as
usual. Take a two to three hour nap in
the late afternoon or early evening to
reduce your sleep debt before the start
of your duties.
During the shift: Take a power nap for
30 minutes if possible to reduce the
sleep debt. Avoid too long a nap as you
may have more difficulty getting into an
Day after the night shift: If you have
to work another night shift, get six
to eight hours of sleep when you get
home. If you cannot get a long enough
sleep, nap in the late afternoon or early
evening as described earlier. If you do
not have to work nights again, catch
a short two to three hour nap after
you get home and stay awake till your
Tips to cope with rotating night
- Maintain a regular sleep routine
on normal work days and on rest
- Plan naps to reduce sleep debt
during night shift periods, and
catch up on sleep on rest days.
- Eat properly and maintain
sufficient exercises to provide
cues for maintenance of
Tips to sleep better during the day:
- Maintain general sleep hygiene
principles. Avoid strenuous
exercises, caffeine and nicotine
four hours before bedtime.
- On your way home from night
shift, use dark sunglasses to
reduce the effects from the bright
morning sunlight which may
influence the circadian rhythm.
- Keep a conducive sleep
environment: Use dark curtains,
and earplugs if necessary.
- Learn some relaxation skills
and avoid trying too hard to
get to sleep.
- Avoid the temptation to defer
sleep to attend to personal
administrative or social tasks –
plan to do these after your
- If necessary, see your GP for shortterm
prescription of sleeping aids.
Use these medications on an as
needed basis only.
Scheduling enough time to sleep
is important and should be actively
prioritised and planned for. Good sleep
is essential to well-being, and allows
one to function efficiently and safely.
Advanced sleep phase syndrome is
more commonly seen in the middleaged
and elderly. This may be due to
the natural shortening of our internal
sleep cycle with increasing age but may
also be contributed to by poor sleep
hygiene and changing sleep habits that
elderly people commonly experience.
Sufferers go to sleep very early in
the evening and wake up in the wee
hours of the morning and are unable
to go back to sleep again. Apart from
the inconvenience and the inability
to partake in evening social events,
insomnia in the early mornings, poor
quality sleep, daytime fatigue and
sleepiness and depression are common
Treatment of Advanced or
Delayed Sleep Phase Syndrome
Consultation with a sleep specialist
is essential for accurate diagnosis
and to exclude other common sleep
conditions. An individualised treatment
plan can then be tailored accordingly
and this may include the following:
- Optimise sleep hygiene and maintain
regular sleep-wake cycles, even on
- Timed bright light exposure with
a special phototherapy device at
specific and individualised timings
- Timed melatonin administration