Circadian Rhythm and Sleep

Last updated: March 6, 2019


Quick Overview

It would be an oversimplification to say that people sleep when it is dark, and stay awake in the light. Yes, to some extent humans are hardwired to sleep at a particular time, under the influence of certain environmental triggers. It is also true that internal factors play an important role too.

Research suggests that sleep happens due to the interaction between numerous factors. Thus there are clock genes, brain centers, hormones, environmental triggers, all interacting with each other continually. There is a need to maintain a balance between sleep and wake.

Circadian rhythm sleep and more

All this means that circadian rhythm does matter, but there are other factors also that play a role in sleep. If you are tired, you may need to sleep even if it goes against your circadian rhythm. Thus, if you did not have enough sleep at night, you may fell asleep in broad daylight. The body needs to maintain the balance between wake and sleep, to stay healthy.

Along with circadian clock or body clock, what matters is how much you slept previously. Less sleep in the past few days may lead to a state called sleep deficit. The condition is very similar to hunger. If you had enough food recently, you do not want to eat. If you didn’t have enough food for long, you would feel strong hunger.

So sleep is the result of the interaction of sunlight (and other environmental factors), social schedule with your internal clocks along with the need to maintain sleep homeostasis. In the modern lifestyle, there are so many factors that can alter sleep. Social pressures, job, may force a person to sleep at different times. All this can cause a shift in circadian rhythm.

Chronic changes in circadian rhythm and sleep pattern may be bad for health. It can lead to metabolic diseases, psychiatric disorders, and depression.

Research shows that sleep problems are more frequent among blind people. Reasons are simple, humans have evolved to sync their internal clock or circadian rhythm with sunlight. Inability to see light means, higher changes of shifts in circadian rhythm. Another good example is shift workers. They get exposed to bright lights at different times. It results in changes in circadian rhythm.

Understanding Circadian Rhythm Sleep Disorders (CRSDs)

These are sleep disorders due to dysfunction of the internal clock. These are the conditions when a person cannot fall asleep at the usual bedtime, or feel sleepy at the odd times. These sleep disorders are now well recognized and are included in the international classification of diseases.

Six CRSDs are:

  1. Delayed sleep phase disorder (DSPD)– in this condition, a person cannot fall asleep. He or she may stay awake in the bed for long. Consequently, a person may have difficulty waking up in the morning.
  2. Advanced sleep phase disorder (ASPD)– these are people who feel too sleepy, and too early. They cannot stay awake late. On the other hand, they cannot remain sleeping in the early morning.
  3. Non-24 Hour Sleep-Wake Disorder (N24HSWD)/Free running disorder– means that circadian rhythm is either longer than 24 hours. It means that a person cannot sleep at a fixed time. Usually, there is a delay of 1-2 hours each day. It results in excessive daytime sleepiness.
  4. Irregular Sleep-Wake Rhythm (ISWR)– means that there is no fixed pattern or time when a person feels like sleeping. It leads to difficulty in going to sleep, and daytime sleepiness.
  5. Jet lag disorder– insomnia caused due to traveling to different time zone.
  6. Shift work disorder– it is due to the nature of work. A person works when he or she has to sleep and sleeps when must be staying active.

Although it may sound that CRSDs are caused due to lifestyle, however, genetics also play a role. That is why there are substantial individual differences in coping with sleep-related problems. Some people are just more sensitive to disturbances of circadian rhythm.

Treating Circadian Rhythm Sleep Disorders (CRSDs)

For decades, researchers have focused on drugs to treat sleep disorders. Thus they prescribed hypnotics, anxiolytics, sedatives. In recent years, melatonin received a lot of attention as a safer option. It can help correct changes in circadian rhythm.

Nonetheless, it is better to treat sleep issues without using drugs. Light therapy can be especially useful in those suffering from jet lag, or for shift workers. It is a strategy of exposing to bright light in the morning for a few hours. Researchers are also studying the effect of light on mood, its role in the treatment of conditions like depression.

In recent years, gadgets have changed their displays. Many devices now adapt light they emit according to the time of the day. Bright blue lights are best avoided in the evening.

Thus to sleep well and keep your biological clock in sync, pay attention to both external stimulants and internal factors. Get out more in the sun, especially in the mornings. Got to bed on time. Similarly, regularize your meal times.

Additional Resources

  1. Dodson ER, Zee PC. Therapeutics for Circadian Rhythm Sleep Disorders. Sleep Med Clin. 2010;5(4):701-715. doi:10.1016/j.jsmc.2010.08.001
  2. Zhu L, Zee PC. Circadian Rhythm Sleep Disorders. Neurol Clin. 2012;30(4):1167-1191. doi:10.1016/j.ncl.2012.08.011

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