Circadian means ‘roughly daily’ and is taken from the Latin terms ‘circa’, meaning about and ‘diem’, meaning day. Circadian rhythms cycle daily according to the 24-hour rotation of the earth, and are internally produced in all living things.
In human beings, circadian rhythms are often called the body clock. We produce, on average, a cycle lasting a bit over 24 hours (with some individual variations). But these internal rhythms are adjusted by external factors on a daily basis – especially sunlight and bright lights. We commonly think of circadian rhythms as controlling our sleep / wake cycle – normal adults usually go to sleep between 10pm – 1am and wake up 7 to 8 hours later. But there are other circadian rhythms at play, including swings in hormones, body temperature cycle, appetite and the naturally best times of alertness and productivity. In an ideal world, these rhythms are all in sync with each other, leading to wakefulness during daylight hours and sleep during darkness. However, when these rhythms get out of sync it can lead to circadian sleep disorders.
Chronic circadian rhythm sleep disorders occur when there are abnormalities of the circadian rhythms – i.e. the body’s internal clock. This leads to people not being able to fall asleep at a normal bedtime, although they can fall asleep at other times. This can cause excessive sleepiness, insomnia or both. There are different subtypes of circadian rhythm sleep disorder, which we will look at individually.
Delayed Sleep Phase Syndrome (DSPS)
Delayed Sleep Phase Syndrome (sometimes called Delayed Sleep Phase Disorder (DSPD)) is a circadian sleep disorder where an individual’s internal body clock is delayed in respect to the day / night cycle.
Those suffering from DSPS are naturally inclined to fall asleep very late at night – usually between 1am and 6am, and will waken in the late morning or afternoon. It is very different from insomnia as, if a sufferer is allowed to follow their natural body clock, they generally have no problems with falling asleep or waking up.
The problems arise when people with DSPS try to live on a normal schedule. If they have to wake up early for work, for example, they will be tired all day but unable to get to sleep any earlier to compensate. A person with DSPS has no choice as to what time sleep onset comes. The lack of sleep that occurs from trying to fit into a ‘normal’ wake cycle causes sufferers to have trouble thinking clearly, driving safely and just generally functioning well. Over time, this sleep deprivation can lead to serious health problems, such as frequent illness and clinical depression.
Some sufferers have found that they can advance their sleep phase to a couple of hours earlier by undertaking light therapy and melatonin treatment, but it’s rare that they can advance it further to a ‘normal’ schedule. The only true solution is to stay on a sleep schedule that their own body clock dictates.
Non 24-Hour Sleep-Wake Disorder (Non-24)
Non-24, also known as hypernychthemeral syndrome or circadian rhythm sleep disorder, free-running type, is a circadian sleep disorder in which the sufferer falls asleep later each day. In general, a sufferer will fall asleep around an hour or two later each day, leading to a circadian cycle of 25-26 hours. Some people with Non-24, particularly those who have lived with the condition for years, do exhibit a much longer delay.
Each daily delay means that a sufferer gradually cycles round the clock, with part of the month spent in a normal cycle of wakefulness in the day and sleep at night. But for the other half of the month, they will find themselves awake throughout the night and sleeping through the day.
This lack of a stable sleep time makes it extremely hard for sufferers to maintain a normal lifestyle – holding down employment, marriage, family life and other social interactions can become impossible. Non-24 can often lead to isolation, poor health, depression and poverty.
Non-24 also often becomes more rigid over time. As sufferers try to fight the body’s urge to sleep at the ‘wrong’ time, they will get chronic sleep deprivation. This leads to increased difficulty in fighting the urge to sleep, and the disorder inevitably becomes more rigid. Many Non-24 sufferers eventually have to admit they have become disabled.
One study has found that up to a third of Non-24 sufferers do respond to treatment (light therapy, melatonin, medication) and can maintain a partially or totally normal sleep schedule.
Advanced Sleep Phase Syndrome (ASPS)
ASPS, sometimes known as Advanced Sleep Phase Disorder (ASPD), is characterised by much earlier than normal bedtimes and wake times. However, sleep quality is normal. Sufferers tend to fall asleep between 6-8pm and will wake naturally eight hours later. This is the opposite problem to those suffering from DSPS and seems to be less common. However, it may simply be that it is diagnosed less often as people with ASPS are usually able to maintain a normal working day without difficulty.
Irregular Sleep-Wake Disorder (ISWD)
Irregular Sleep-Wake Disorder (ISWD) is characterised by at least three sleep episodes per 24-hour period, which occur irregularly from day to day. It usually has an underlying cause and is most commonly found in elderly patients suffering from dementia. It is also found in children with developmental disorders such as autism and as a consequence of brain tumours or traumatic brain injury in both children and adults.
Shift Work Disorder
Although caused by external behavioural factors, Shift Work Disorder is classified as a Circadian Rhythm Disorder (CRD). It occurs when work schedules force people to be awake when their natural circadian rhythms dictate that they should be asleep. Some people adjust to shift work better than others. But for those whose body clocks cannot shift sufficiently, chronic sleep deprivation occurs and the shift work results in a circadian sleep disorder.
Most of us are familiar with jet lag, which is the result of travelling across time zones. Night time begins either several hours earlier or several hours later in the new time zone than it did in our normal time zone. This means that the sleep / wake cycle needs to shift, along with all other circadian rhythms. However, they often don’t shift together. The shift in sleep hours may in itself cause significant tiredness, with the desynchronisation of the various circadian processes causing additional fatigue. However, over a number of days the various body clocks will adjust to the new day / night cycle.