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Circadian Rhythm and Sleep

Quick Overview

People sleep when it’s dark and stay awake when it’s light. It’s a simple concept but it doesn’t completely explain our sleep cycle. 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.

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

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. If you didn’t get enough sleep at night, you may even fall asleep in broad daylight. The body needs to maintain the balance between sleep time and wake time.

Along with your circadian clock – also known as your body clock – what matters most is how much you’ve previously slept. If you get insufficient sleep over the course of multiple days it may lead to a state called sleep deficit. The condition is very similar to the feeling of hunger. If you had enough food recently then you’re satisfied you do not want to eat. If you didn’t have enough food, you’ll feel intense hunger pangs. Your sleep deficit functions in a similar way.

Sleep is the result of the interaction of sunlight (and other environmental factors) and your social schedule with your internal clock combined with the need to maintain sleep homeostasis. With our hectic modern lifestyles, there are so many additional factors that can alter sleep. Social pressures and your job may force you to sleep at different times. All this can cause a shift in circadian rhythm.

Chronic changes in your circadian rhythm and sleep patterns may be bad for your health. You can end up with metabolic diseases, psychiatric disorders, and/or depression.

Research shows that sleep problems are more frequent among blind people. The reason is simple: humans have evolved to sync their internal clock – or circadian rhythm – with sunlight. Inability to see light means that your body is less likely to maintain a consistent internal clock. Shift workers are another good example of people have an out-of-sync circadian rhythm. They get exposed to bright lights at different times, which results in frequent changes in their circadian rhythm.

Understanding Circadian Rhythm Sleep Disorders (CRSDs)

Circadian rhythm sleep disorders are caused by a dysfunction of the internal clock. These are the conditions that explain what happens when a person cannot fall asleep at their usual bedtime or feels tired at the wrong time of day. 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)– A person who has this condition can not fall asleep. He or she may stay awake in bed for a long time. Consequently, they may have difficulty waking up in the morning.
  2. Advanced sleep phase disorder (ASPD)– This disorder applies to people who feel extremely tired well before their bedtime. They cannot stay awake late. On the other hand they cannot stay asleep in the early morning.
  3. Non-24 Hour Sleep-Wake Disorder (N24HSWD)/Free running disorder– This disorder describes a condition where the circadian rhythm is longer than 24 hours. It means that a person cannot sleep at a fixed time. There is usually a delay of 1-2 hours each day. It results in excessive daytime sleepiness.
  4. Irregular Sleep-Wake Rhythm (ISWR)– With this condition there is no fixed pattern or time when a person feels like sleeping. It leads to difficulty in going to sleep and increased daytime sleepiness.
  5. Jet lag disorder– Jet lag disorder is insomnia that is caused by traveling between time zones.
  6. Shift work disorder– This disorder is caused by not working at a consistent time each day. A person works when he or she has to sleep and sleeps when they should be staying active.

Although it may sound like CRSDs are caused exclusively due to lifestyle factors, 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 including hypnotics, anxiolytics, sedatives. Melatonin received a lot of attention as a safer option in recent years because it is a natural way to help correct changes in circadian rhythm.

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

There are many blue light-blocking glasses and apps than can reduce the amount of blue light emitted by your phone or computer at night. Your body can’t differentiate the difference between the light from the sun and the blue light that your computer and cell phone emit at night. It’s best to reduce your exposure to artificial blue light at night to improve your circadian rhythm.

If you want to sleep well and keep your biological clock in sync, pay attention to both external stimulants and internal factors. Spend more time out in the sun, especially in the mornings. Go to bed on time. Eat your meals at regular times. These simple steps can help you regulate your circadian rhythm and sleep better.

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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