If someone experiences Circadian Rhythm Sleep Disorder, it means they’re unable to fall asleep and awaken at the appropriate times: by this we mean the times normally required by work, school, and social needs. When people who have CRSD are allowed to use their body-clocks to dictate when to go to sleep and when to awaken, they generally get enough sleep; and interestingly, their sleep quality is quite normal unless they also have another sleep disorder.
Like most other living organisms, humans have various biological rhythms. Body processes that re-occur daily, such as alertness, hormone secretion, body temperature, and sleep timing, are controlled by circadian rhythms – which we also know as our biological clock or our body clock. Because of a human’s circadian clock, sleepiness doesn’t continue increasing as the day goes by. A person’s ability and desire to fall asleep is influenced by both internal circadian rhythms and the length of time since the person awoke from a satisfactory sleep. Therefore, our body is ready for sleep and for waking at quite specific times of the day.
Yaron Dagon, a sleep researcher, stated that CRSD can lead to harmful functional and psychological difficulties, and that these disorders are often misdiagnosed and thus incorrectly treated simply because doctors are not aware of their existence.
Types of Circadian Rhythm Sleep Disorders
There’s one (1) ‘Extrinsic’ CRSD and four (4) ‘Intrinsic’ CRSD, as follows –
The word ‘extrinsic’ comes from the Latin extrinsecus, meaning on the outside, from without – or circumstantial.
- Shiftwork Sleep Disorder
This disorder affects people who work on rotating shifts or night shifts. In the past, jetlag was also classified as an extrinsic type of CRSD.
The word ‘intrinsic’ comes from the Latin intrinsecus, meaning inwardly, on the inside – or built in.
- ASPD, which stands for Advanced Sleep Phase Disorder
ASPD is also known as Advanced Sleep Phase Syndrome (ASPS). It’s typically characterized by difficulty in staying asleep in the morning and difficulty staying awake in the evening. A person will feel sleepy and go to bed very early in the evening – between (say) 6 and 8 pm, then wake up very early in the morning – around (say) 3 am.
- DSPD, which stands for Delayed Sleep Phase Disorder
DSPD is also known as Delayed Sleep Phase Syndrome It’s defined by the onset of sleep which occurs later-than-normal, followed by a peak period of alertness during the night. Typically, people with DSPD fall asleep sometime after midnight and have difficulty waking up in the morning.
Irregular Sleep-Wake Rhythm presents as a person sleeping at irregular times, often more than twice per day; however, the person has a total time asleep typical for their age. Basically, the person wakes frequently during the night and makes up for their lack of sleep by napping during the day.
This disorder is also known as Hypernychthemeral Syndrome. With this disorder, each day the person’s sleep occurs later and later, and, accordingly, so too does the peak period of alertness
Normal Circadian Rhythms
There’s a continuum of chronic types among people with healthy circadian clocks, ranging from ‘morning’ people (larks) who prefer to go to sleep early and awaken early, to ‘evening’ or ‘night’ people (owls), who prefer to go to sleep late at night and awaken late in the morning. Regardless of whether people are larks or owls, those with normal circadian systems can –
- Wake up and go to sleep at the same time every day, if they choose to;
- Fall asleep at night allowing enough sleep time before having to get up, and can awaken in time for whatever they need to do in the morning;
- Start to fall asleep earlier each night and get up earlier than usual within just a few days, if a new routine so requires. Adapting to an earlier sleep/wake time is known as ‘advancing the sleep phase’, and it’s very possible for healthy people to advance their sleep phase by approximately one hour each day.
Interesting Sleep Research
In one lot of research, volunteers were placed in special apartments or caves for several weeks, with no clocks or other time cues. Interestingly, without time cues, these volunteers went to bed roughly an hour later and awoke roughly an hour later each day. The results of these experiments appeared to show that humans have a free-running circadian rhythm of approximately 25 hours.
However, because these volunteers were able to control artificial lighting and the evening light caused a phase delay, more research was carried out. This new research showed that all adults free-run at an average of just over 24 hours (24 hours and 11 minutes, to be precise!). Our biological clock requires regular environmental time-cues in order to maintain a 24-hour day/night cycle. These time-cues, also known as zeitgebers, include our daily routine, and sunset and sunrise. We need time-cues to keep our normal human circadian clock aligned with the rest of the world.