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What Is Circadian Rhythm?

SCOFA-Circadian-Rhythm-c1

 
Medically reviewed by
Dacelin St Martin, MD
Triple board-certified in Sleep Medicine,
Internal Medicine, and Pediatrics.

 
 
Circadian Rhythm Work? | Affect Your Sleep? | What Happens If | What Can Alter Your Circadian Rhythm? | How Can You Maintain

 

Overview

All living things have an internal clock that changes based on environmental elements, like light and temperature.[1] These patterns are called circadian rhythms. 

The circadian rhythm controls many things our bodies do, including sleep. The sleep-wake cycle is one of the best-known and most critical circadian rhythms. 

When your circadian rhythm is correctly synchronized, it can facilitate constant and restorative sleep. However, when one’s circadian rhythm is disrupted, it can cause serious sleeping issues, such as insomnia. 

In addition, research indicates that circadian rhythms influence many crucial physical and mental health areas.

This article will elaborate on the circadian rhythm, how it works and how it influences your sleep.

 

How Does Circadian Rhythm Work?

Circadian rhythms are found in all living things. They function by ensuring that the complex operations in everyone’s bodies are optimized at specific times throughout the day.[2]

For instance, circadian rhythm influences the action of nocturnal animals; it makes them rest during the day and search for food at night when it may be easier to avoid predators. 

In humans, the circadian rhythm helps to synchronize everyone’s mental and organ systems to maximize productivity and functionality.[3]

For instance, it programs the brain to be at its most alert state at work or school. It also synchronizes the production of digestive enzymes that help in the breakdown of food with your typical mealtime.[4]

The circadian rhythms in the body are linked to a master clock in the brain.[5] It’s otherwise known as the circadian pacemaker.[5] It’s located in the suprachiasmatic nucleus (SCN) of the hypothalamus a part of the brain. Also, clock proteins in the suprachiasmatic nucleus (SCN) deliver signals at specific times during the day to regulate activity across the body.[6]

The SCN is extremely sensitive to light. So, light acts as an essential external cue in influencing the signals transmitted by the SCN to coordinate the body’s circadian rhythms. 

As a result, circadian rhythms are intimately linked to day and night. While other factors such as exercise, temperature, etc, can influence one’s biological clock, light has the most significant impact on circadian rhythms. 

 


 

How Does Circadian Rhythm Affect Your Sleep?

One of the most evident and fundamental examples of the circadian rhythm is the sleep-wake cycle, which influences your sleep and wake time. 

During the day, exposure to light triggers your biological clock to send signals that generate wakefulness.[1] It helps you stay alert and active. 

As darkness falls, your internal clock commences the secretion of melatonin. This hormone induces sleep and keeps you asleep throughout the night. 

In this manner, your circadian rhythm synchronizes your sleep-wake time with day and night, creating a steady restful sleep cycle that lets you do more during the day.

Aside from the sleep-wake cycle, other vital influences of the circadian rhythm include:

  • The control of blood sugar and cholesterol levels, which in turn affects metabolism and body weight[7]
  • Association with mental health and risk for mental disorders[8]
  • The functioning of the immune system[9]

 

What Happens If Your Circadian Rhythm Is Disrupted?

When your circadian rhythm is disrupted, your body’s processes cannot work correctly. 

A person may find it difficult to fall asleep, may wake up frequently while sleeping, or wake up too early in the morning. 

For instance, when one’s sleep-wake cycle is disrupted, it may lead to significant sleep troubles. In addition, alteration of the circadian rhythm can result in shorter total sleep time, shallower and fragmented sleep, and poor-quality sleep. 

Furthermore, circadian rhythm abnormalities are probable contributors to obstructive sleep apnea (OSA) a disorder characterized by recurrent interruptions in breathing.[10] Obstructive sleep apnea (OSA) lowers the body’s oxygen levels and disrupts sleep often during the night. 

A misaligned circadian clock can disrupt sleep, including raising the risk of insomnia and inappropriate daytime sleepiness. Given the importance of sleep for wholesome health, there are typically severe implications when a person’s circadian rhythm is off.

 

What Can Alter Your Circadian Rhythm?

Alterations to one’s circadian rhythm can occur short- or long-term. Sleep experts have classified circadian rhythm sleep-wake disorders (CRSWD) into several categories based on the symptoms and factors contributing to their development:[11]

  1. Jet Lag Disorder: This disorder occurs when a person travels through many time zones in a short amount of time. It was given this name because persons who take transcontinental flights repeatedly experience this condition. People with jet lag are more prone to have sleep troubles and weariness until their circadian rhythm adjusts to the new location’s day-night cycle.
  2. Shift Work Sleep Disorder (SWSD): Work demands can throw one’s circadian cycle out of whack. Some work shifts, which demand working through the night and sleeping during the day, may cause a person’s sleep cycle to be disrupted.
  3. Delayed Sleep Phase Disorder (DSWPD): This disorder is typically linked to people with the “night owl” sleep chronotype (i.e., those who stay up late before sleeping). The specific cause is unknown. However, it’s suspected that genetics, underlying medical issues, and a person’s behavior may play a role in its development.
  4. Advanced Sleep Phase Disorder (ASWPD): People with this disorder become exhausted early in the evening and awaken early in the morning. People with an advanced sleep phase problem cannot typically stay up late at night or get more sleep in the morning, even if they wish 
  5. Non-24-Hour Sleep-Wake Disorder (N-24): This disorder primarily affects blind individuals who cannot receive light-based signals for their circadian rhythm. Typically, in non-24-hour sleep-wake rhythm disorder, the body maintains a 24-hour cycle. However, the usual sleeping hours continually advance by minutes or hours.
  6. Irregular Sleep-Wake Disorder (ISWD): This uncommon disorder is characterized by a lack of a stable sleep pattern and many naps or short periods of sleep throughout 24 hours. It is frequently associated with brain conditions, such as dementia or traumatic brain injury. It impairs the hypothalamic biological clock’s functioning.

 

How Can You Maintain A Stable Circadian Rhythm?

Keeping a steady and healthy circadian rhythm is vital to your overall health. Here are a few tips to help maintain a stable circadian rhythm.

  • Sunbathing: Exposure to sunlight, particularly early in the day, reinforces the most potent circadian rhythm trigger.
  • Maintain a Regular Sleep Schedule: Changing your bedtime or wake-up time can interfere with your body’s ability to acclimatize to a stable circadian rhythm.
  • Exercise Every Day: Activity during the day may boost your biological clock and make falling asleep at night easier.
  • Reduce Caffeine Intake: Stimulants like caffeine can keep you awake and disrupt the equilibrium between sleep and wakefulness.
  • Reduce Exposure to Light Before Bedtime: Exposure to artificial light at night can disrupt the circadian rhythm. Sleep experts recommend that you dim the lights and put down electronic gadgets in the hours leading up to bedtime.

If you constantly get exhausted throughout the day or have trouble sleeping through the night, you should talk to your sleep doctor. Also, ask your doctor about ways to avoid jet lag or sleep disruption if you work shifts or plan to travel across time zones.

 

Reference:

    1. S, Reddy S; Reddy V; Sharma. “Physiology, Circadian Rhythm.” National Center for Biotechnology Information, U.S. National Library of Medicine, https://pubmed.ncbi.nlm.nih.gov/30137792/.
    2. National Institute of General Medical Sciences. Circadian Rhythms. https://www.nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms.aspx.
    3. Sollars, P. J., & Pickard, G. E. (2015). The Neurobiology of Circadian Rhythms. The Psychiatric clinics of North America, 38(4), 645–665. https://doi.org/10.1016/j.psc.2015.07.003.
    4. Carlson, E., Machalek, A., Saltsman, K., & Toledo, C. (2012, November 1). Tick Tock: New Clues About Biological Clocks and Health. https://www.nigms.nih.gov/education/Inside-Life-Science/Pages/tick-tock-new-clues-about-biological-clocks-and-health.aspx.
    5. Fults, E. (2011, March 8). The Rhythms of Life. https://www.nigms.nih.gov/education/Inside-Life-Science/Pages/The-Rhythms-of-Life.aspx.
    6. Carlson, E. (2014, March 6). Resetting Our Clocks: New Details About How the Body Tells Time. https://www.nigms.nih.gov/education/Inside-Life-Science/Pages/Resetting-Our-Clocks-New-Details-About-How-the-Body-Tells-Time.aspx.
    7. Jagannath, A., Taylor, L., Wakaf, Z., Vasudevan, S. R., & Foster, R. G. (2017). The genetics of circadian rhythms, sleep, and health. Human molecular genetics, 26(R2), R128–R138. https://doi.org/10.1093/hmg/ddx240.
    8. MedlinePlus [Internet]. Bethesda (MD): National Library of Medicine (US); [updated 2019 Aug 27]. Degenerative Nerve Diseases. Available from https://medlineplus.gov/degenerativenervediseases.html.
    9. Sancar, A., Lindsey-Boltz, L. A., Gaddameedhi, S., Selby, C. P., Ye, R., Chiou, Y. Y., Kemp, M. G., Hu, J., Lee, J. H., & Ozturk, N. (2015). Circadian clock, cancer, and chemotherapy. Biochemistry, 54(2), 110–123. https://doi.org/10.1021/bi5007354.
    10. Butler, M. P., Smales, C., Wu, H., Hussain, M. V., Mohamed, Y. A., Morimoto, M., & Shea, S. A. (2015). The Circadian System Contributes to Apnea Lengthening across the Night in Obstructive Sleep Apnea. Sleep, 38(11), 1793–1801. https://doi.org/10.5665/sleep.5166.
    11. Wagner, Daniel R. “Disorders of the Circadian Sleep–Wake Cycle.” Neurologic Clinics, Elsevier, 21 June 2005, https://www.sciencedirect.com/science/article/abs/pii/S0733861905702784.
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