What is Circadian Rhythm?

What Are Circadian Rhythms?

Circadian rhythms are bodily systems in the body that follow a roughly 24-hour cycle and repeat each day. These consistent rhythms control the body’s sleep/wake cycles — when you fall asleep and when you awaken — as well as other important processes like metabolism, body temperature, and hormones.1

Circadian rhythms are primarily regulated by light, but can also be influenced by other external cues like temperature, exercise, and social interactions.2 These cues influence the body’s master clock, the suprachiasmatic nucleus (SCN). For example, when the external environment becomes dark, the SCN turns on circadian rhythm genes and tells the body to produce melatonin, a hormone that makes you feel more tired. In this way, cues like light affect your sleep timing.1

Circadian rhythms are one of two processes in your body that help regulate sleep. The other is the sleep drive, which is the biological need for sleep.3 The longer you are awake, the more your sleep drive increases and the greater your need to go to bed. The sleep drive and circadian rhythms work together to control when you feel sleepy and how deeply you sleep.4

What Else Do Circadian Rhythms Affect Besides Sleep?

Circadian rhythms influence health in many ways. For example, disruptions in circadian rhythms and sleep deprivation are linked to chronic health conditions like:5

Metabolic disorders, including obesity, diabetes, and hypertension (high blood pressure)
Mood disorders like depression, seasonal affective disorder, and bipolar disorder
Neurodegenerative disorders like Alzheimer’s disease and Parkinson’s disease
Immune system disorders and inflammatory conditions
Cancer

Causes and Symptoms of Circadian Rhythm Disorders

Health problems can occur when the body’s circadian rhythms get out of sync with the light-dark cycles that are happening in the environment. In the short term, circadian disorders can be temporarily disrupted by things like jet lag, in which traveling across multiple time zones causes irregularities in sleep and wake times.6

Circadian rhythm disorders can develop due to more long-term causes. These may include:6

Working the night shift
Having sleep habits that don’t align with light-dark cues in the environment
Developing certain medical conditions
Having certain gene mutations

Symptoms of circadian rhythm disorders can include insomnia and fatigue as well as trouble concentrating, focusing, remembering, or making decisions.6

What Are the Long-Term Benefits of Healthy Sleep Habits for Adults?

Healthy sleep habits can help you optimize the hormones in your brain that reinforce your body’s internal clock, causing you to fall asleep and wake up with consistency and ease.

Following a good sleep schedule also allows your body to make growth hormone, which helps build muscle and repair damage, and sex hormones, which help control fertility.7

Healthy sleep patterns also allow your brain, heart, and other organs to rest, strengthening your memory, improving your cardiovascular system, and helping protect against disease.7

How Can You Reset, Regulate, and Improve Circadian Rhythms?

You can influence your circadian rhythms by changing when your body is exposed to light. Bright light from the sun or from lights in your house signals to your body that it is daytime, resetting the processes in your body that control your circadian rhythms.1 In particular, it is important to be exposed to bright light soon after you wake up, to help reinforce to your circadian rhythms that it is daytime.8 Resetting your circadian rhythms requires daily exposure to light and can take several weeks to effectively shift.

The blue light that emits from electronics screens may also be a factor. Some research has found that blue light lowers the amount of melatonin that your body produces, shifting your circadian rhythms and delaying your sense of sleepiness later in the evening.9

However, other research has found that blue light doesn’t disrupt circadian rhythms as much as previously suspected.10 You will benefit from finding what level of exposure works for you. It’s possible that the stress of avoiding screens might be worse for sleep than the screens themselves.

To maintain consistent circadian rhythms, it helps to develop long-term habits. Wake up at a similar time each day, get lots of bright light in the mornings, and go to bed at the same time each evening. This can keep the genes, hormones, and other factors that influence your circadian rhythms operating on the same schedule each day.

For personalized advice on improving your own circadian rhythm, fill out our questionnaire. Dawn can connect you to a sleep coach who can help you understand the best next steps to take.

References

National Institute of General Medical Sciences. (2021, September 9). Circadian Rhythms. https://www.nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms.aspx
National Institute on Alcohol Abuse and Alcoholism. Overview of Circadian Rhythms. https://pubs.niaaa.nih.gov/publications/arh25-2/85-93.htm
Centers for Disease Control and Prevention. (2020, March 31). NIOSH Training for Nurses on Shift Work and Long Work Hours. https://www.cdc.gov/niosh/work-hour-training-for-nurses/longhours/mod2/11.html
Borbély, A. A., Daan, S., Wirz-Justice, A., & Deboer, T. (2016). The two-process model of sleep regulation: a reappraisal. Journal of sleep research, 25(2), 131–143. https://doi.org/10.1111/jsr.12371
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
National Heart, Lung, and Blood Institute. (2019, September 25). Circadian Rhythm Disorders. https://www.nhlbi.nih.gov/health-topics/circadian-rhythm-disorders
MedlinePlus. (2021, December 28). Healthy Sleep. https://medlineplus.gov/healthysleep.html
Centers for Disease Control and Prevention. (2020, April 1). Effects of Light on Circadian Rhythms. https://www.cdc.gov/niosh/emres/longhourstraining/light.html
Chang, A. M., Aeschbach, D., Duffy, J. F., & Czeisler, C. A. (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences of the United States of America, 112(4), 1232–1237. https://doi.org/10.1073/pnas.1418490112
Mouland, J. W., Martial, F., Watson, A., Lucas, R. J., & Brown, T. M. (2019). Cones Support Alignment to an Inconsistent World by Suppressing Mouse Circadian Responses to the Blue Colors Associated with Twilight. Current biology: CB, 29(24), 4260–4267.e4. https://doi.org/10.1016/j.cub.2019.10.028