With sleep and circadian rhythms, it is observed in everything from plant and animals to fungi and bacteria – and of course humans. The term circadian is from the Latin circa, meaning “around” and dies / diem which means “day” – giving us a literal definition of “about a day”.
It is a kind of built in clock that tells us when to be awake and when we should be sleeping. This “clock”, whose scientific name is suprachiasmatic nuclei (SCN), rests in a region of the brain around where the optic nerves cross. The SCN is adjusted primarily by daylight but also by other external time cues called zeitgebers – which can be anything from the beeping of your alarm to the timing of specific meals. Light reaching this area through the retina, are turned into signals which continue their way up the optic nerve, finding its way to the SCN.
The suprachiasmatic nuclei has many functions, sending out signals to many different areas of the brain which control things like the production of melatonin and the secretion of other hormones, the production of urine, the governing of body temperature as well as changes in our blood pressure.
Scientific studies (in particular one done by Czeisler et al. at Harvard) have proven that the free-running range of a healthy adult’s circadian rhythm is about 24 hours and 11 minutes (plus or minus 16 minutes). Basically, our body’s clock follows the same cycle as the 24 hour rotation of the Earth.
We’ve already learned that light resets our biological clock or our suprachiasmatic nuclei. Light also has the ability to delay or advance our circadian rhythm depending on the timing, the type of light and the amount of light. It is not known exactly at what levels light starts to affect our sleep and circadian rhythms but some researchers believe the number to be upwards of 1000 lux.
Sleep and circadian rhythms – Disruptions
We’ve learned that both light and timing play an important role between the association of sleep and circadian rhythms. Disruptions in your circadian rhythm can cause sleeping disorders as well as other issues such as general fatigue, loss of appetite, lack of alertness etc. These symptoms, which are normally associated with a lack of sleep, are referred to as circadian rhythm sleep disorders.
Circadian Rhythm Sleep Disorders
Circadian rhythm sleep disorders can be classified into two groups – extrinsic (external) and intrinsic (internal). Extrinsic types of circadian rhythm sleep disorders are when something external causes your sleep problems. These include jet lag and shift work sleep disorder.
Intrinsic types of circadian rhythm sleep disorders include:
- Delayed Sleep Phase Syndrome (DSPS) – going to bed and waking up later than “regular” people
- Advanced Sleep Phase Syndrome (ASPS) – having trouble with both staying awake in the evening and staying asleep in the morning.
- Non-24-Hour Sleep-Wake Syndrome (Non-24) – going to bed later and later each day, never being able to develop any type of sleep schedule
- Irregular Sleep-Wake Rhythm – sleeping at very irregular times throughout the day – including naps – but overall sleeping the same amount of time as healthy sleepers.
To combat some of these sleep and circadian rhythm issues, some doctors recommend bright light therapy. People undergoing bright light therapy are exposed to bright lights that manipulate the body’s clock, helping them adjust to a new sleep time or a new time zone.
Circadian rhythm sleep disorders are very dangerous as they can lead to accidents in the workplace or while on the road. It is said that the accidents at Three Mile Island, Chernobyl and the Exxon Valdez oil spill were attributed to night-shift workers’ fatigue.
Anther circadian rhythm sleep disorder “cure” includes the use of melatonin supplements. Since melatonin is a naturally produced hormone which increases after dark and makes us feel sleepy, taking these supplements at optimal times have proven to be effective in aiding in sleep and circadian rhythms problems.