What Is Circadian Rhythm & How Does It Work?

What Is Circadian Rhythm & How Does It Work?

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Last Updated on Mar 22, 2023

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    Through your 24 hour schedule you'll notice your body automatically shutting down at night and starting its functions again in the morning. How does your body know when to do so?

    These functionalities of your body occur due to your body’s 24-hour clock or biological clock called circadian rhythm. This clock ticks and alerts the body to carry out certain functions throughout the day. But sometimes, a malfunction occurs in this clock that causes a disruption of these cycles, which can significantly deteriorate your health. 

    So, to stay ahead of such consequences, it is imperative to know what circadian rhythm is and how any change can affect your physical and mental health!

    What Is Circadian Rhythm?

    Scientifically, circadian rhythm is used to define the changes, be it mental, physical, or behavioral, that a body goes through within 24 hours. It ensures that the body remains optimized to carry out its regular activities without a hitch. 

    The most common circadian rhythm found in all living species is the sleep-wake cycle. And it is through these cycles, they achieve a consistent and therapeutic sleep schedule. 

    The circadian rhythms work in the background of the body’s internal biological cycle and regulate aspects like hormone secretion, metabolism regulation, control of body temperature, waking hours, etc. Each body organ has its circadian rhythm that gets synchronized with the central clock residing in the brain. And this main clock receives the cue from the environment to project any necessary changes. 

    How Does Circadian Rhythm Work?

    As we mentioned, every living species on the planet has its biological clock, which determines the time they need to carry out during a specific time and the hormonal and temporal requirements to fulfill it. It predominantly occurs in response to the lifestyle or habits that they tend to have and day/night activities. 

    For animals, it helps determine the release of proteins by the digestive system to match the typical food intake hour and hormones like melatonin and cortisol during physical exertion or rest time. It schedules the time for when the petals would open or close for plants. 

    The main clock or circadian pacemaker is located in the brain and controls all the circadian rhythms that a body is known to have. Specifically, it refers to the culmination of 20,000 nerve cells that make up the suprachiasmatic nucleus (SCN). It can be found in the hypothalamus, a part of your brain. This SCN then sends signals at different times through clock genes, which helps in the required regulation. 

    SCN is highly susceptible to changes in the light and dark and is affected quite heavily by it. So, as soon as it notices a difference in the light form, it immediately signals to maintain the body’s internal clock. Being this sensitive to light implies that the circadian rhythms see apparent changes in response to day and night. 

    And while social activity, exercise, and temperature are also some well-known and often used cues, the light changes remain the biggest determiner of circadian rhythms.

    Circadian Rhythm in Babies

    Circadian rhythms are not developed in babies until after a few months. This implies that since their bodies do not have any fixed schedule to follow, their sleep schedule can be pretty erratic. These rhythms eventually develop as they start understanding the changes in the environment, and their bodies become accustomed to certain practices at a fixed time. 

    Most babies start releasing melatonin when they reach three months, and by nine months, they begin releasing cortisol—owing to this, babies over ten months old start developing a sleep schedule. As they mature, their circadian rhythm starts responding to their bodily functions, which ultimately helps fulfill their 9 hours of sleep requirements.

    Circadian Rhythm in Kids/Teens

    As children grow up into kids and teenagers, they experience a shift in their circadian rhythm, known as the sleep phase delay. While undergoing this change, teens no longer feel tired or drained around 8 P.M. or 9 P.M. 

    Melatonin, the sleep hormone responsible for causing sleep, does not release until 10 or 11 PM. This implies that the sleep loss is made up later in the day, as their sleep requirements remain the same, which causes them to wake up late in the morning. 

    The peak sleep hours on which they receive definitive sleep is between 3 AM to 7 AM.

    Circadian Rhythm in Adults

    Once they hit adulthood, the sleep requirements become subjected to the habits and conditions of the individual. But objectively, it is requisite to maintain proper and healthy sleep hygiene to deal with the exertion of their daily activities. 

    Getting 7 to 9 hours of sleep is essential to ensure that the body gets time to make up for the labor it went through the day. Adults have melatonin released at around midnight, and they experience peak sleep at  2 to 4 AM and 1 to 3 PM. 

    Older adults tend to experience a significant shift in their Circadian Rhythm, as they find themselves asleep earlier than usual and awake very early. This change is nothing unusual, and just a part of growing up. 

    Is a Circadian Rhythm the Same As a Biological Clock?

    Circadian rhythm is part of the Biological clock and is directly affected by it. Biological clocks help regulate the timing of all bodily functions, which includes circadian rhythm. Hence, all Circadian rhythms are a part of the Biological clock, but not all Biological clocks are circadian Rhythms. 

    For example, human beings go through changes in their habits as seasons change through the year, which has nothing to do with the circadian Rhythms of 24 hours clock.

    Circadian Rhythm and Sleep

    The sleep-wake cycle is the most critical and talked about circadian rhythm. These sleep-wake Circadian rhythms directly determine your sleep schedule and when you are most likely to sleep. 

    In the mornings, due to the light exposure, the SCN signals the body to stay awake and be alert. And as the night starts falling, melatonin is released, which sends the signals of going to sleep. This hormone is released throughout the night to ensure that you stay asleep. 

    In this way, circadian rhythm ensures that we are given the right cues throughout the day to carry out the required functionalities. This sleep clock aligns our activities with the day and night schedule and promotes activities that suit it. 

    Circadian Rhythm and Your Health

    Besides affecting the sleep schedule, circadian rhythm also plays an integral role in functioning all body parts. 

    Research suggests that circadian rhythm affects metabolism and weight by regulating blood sugar and cholesterol. It also bears an influence on your mental health. This includes a direct effect on the development of psychiatric illnesses like bipolar disorder and depression and neurodegenerative diseases like Alzheimer’s. 

    The DNA repairing cells that prevent the probability of cancer and the entire immune system, too, stands affected by the circadian rhythm of your body. It can also help determine how effective the anti-cancer drugs will prevent the disease. New medications are suggesting the use of this biological cycle against it.

    What Happens When Circadian Rhythm Gets Off Track?

    A simple change in the circadian rhythm could mean the complete disruption of the body functions. When the rhythm goes off the track, the organs cannot function optimally as they don’t get the requisite sleep or hormone to deal with the situations. 

    In the case of sleep-wake circadian rhythm being off, the body does not meet its sleeping requirements. If the body’s internal clock does not send the cues to the organs, they can’t take action that suits the particular time. 

    It could cause sleeping problems like not going to sleep at times, waking up at ungodly hours, or waking up constantly throughout the night.

    Research studies have identified that this could lead to obstructive sleep apnea (OSA), one of the sleep disorders that can cause lapses in breathing. It significantly reduces the oxygen intake at night and causes a person to wake up repeatedly. 

    Sleeping disorders like Insomnia and excessive daytime sleepiness can be rampant due to this misalignment of the circadian rhythm. Your productivity throughout the day will also decrease, given how you will be drowsy and sleepy due to the lack of proper rest. 

    What Can Disrupt Your Circadian Rhythm?

    Numerous circadian rhythm sleep-wake disorders (CRSWD) can occur owing to their different characteristics and causes. And all of these causes of circadian rhythm disorders can occur over a short or extended period. The experts identify the following:

    Non-24 Hour Sleep-Wake Disorder: 

    The Non-24-hour Sleep-Wake Disorder is found mainly amongst blind people. Since they cannot gauge their circadian rhythm due to light cues, their sleep schedule is often backward by a few minutes, seconds, or hours. But they are still capable of following a 24-hour cycle. 

    Shift Work Disorder: 

    The shift work disorder is a significant sleep disorder faced by people who work through the night instead of the regular daytime. Their schedule goes directly against the circadian rhythm, which conforms the body to stay awake during the day. 

    Advanced Sleep Phase Disorder: 

    People going through this sleep disorder find themselves awake early in the morning and tired in the evening, which is the Irregular Sleep-Wake Ciracadina Rhythm Disorder. They also find difficulty staying up, sleeping at night, and waking up late in the morning. It is a relatively rare disorder that affects only 1% of the population and is generally found in older adults. It can be either developed over time or occur due to inherited genetic causes. 

    Irregular Sleep-Wake Rhythm Disorder: 

    Another rare sleeping disorder throws people off schedule and makes it impossible to have a consistent sleep schedule. They might take a nap or two throughout the day, but it is never constant. This disorder can result from some traumatic experience or neurodegenerative diseases like dementia. 

    Jet Lag Disorder:

    This circadian rhythm sleep disorder occurs when a person goes through several time zones within a short period of time. It is often experienced by intercontinental flyers who cross at least one if not multiple time zones through a single flight. The body takes time to get adjusted to the new time zone, and until it does so, the flier will continue experiencing fatigue and restlessness. 

    Delayed Sleep Phase Disorder:

    People who go through this sleep disorder are often deemed ‘Night Owls’ or ones that can stay awake throughout the night and then sleep through the morning. Like Advanced Sleep Phase Disorder, it is rare to find and occurs in just 1 or 2 people out of every 1,000. The disorder is rampant amongst teenagers due to genetic causes, physical conditions, and behavior. 

    As observed, all these sleeping disorders stem from different issues. They can be short-term and can be cured within a few days. Others have a long-term implication due to underlying problems that can presumably stay with them for years to come. Jet lag and shift work can affect the 24-hour sleep cycles but is easily curable by letting the body adjust for a while.

    But it is the remaining disorders that can take a toll on the individuals and significantly affect their mental or physical health. These circadian rhythm sleep-wake disorders can have a long-term effect like Insomnia which can render them physically tired with no incentive to work or take care of themselves.

    How to Reset Circadian Rhythm

    While it might be possible to fix the circadian rhythm of your body entirely as we do not have control over it, there are specific tips you can follow that could give you better 24-hour sleep cycles: 

    • Going out in the sun - Attaining strong sunlight, especially during peak hours, can restore the light cue of the circadian rhythm.
    • Maintaining a sleep schedule - Going to bed and waking up in the morning at fixed points of the day can help create a stable circadian rhythm. This would mean that your body will know when it needs to release melatonin or wake you up at the desired time. 
    • Say no to caffeine - While a strong caffeine sound pleasing, the drink can throw your schedule off and make it impossible to go to sleep even if your body needs it.
    • Get rid of blue lights - Lights are the cue for your body to wake up. So, avoid a lot of lights because it might make the SNC think that it is still daytime. Especially blue light exposure right before bed. Avoid using electronics like TV, Mobile, Tablets, etc. 
    • Workout daily - Working out will exhaust your body and naturally seek sleep. 
    • Only short naps in the afternoon or evening - Sleeping for too long in the afternoons and evening won’t make your body asleep, which can throw your circadian rhythm off. 

    • Get comfortable - Get yourself a cozy bed with the right temperature and dim lights. This will automatically relax your body and put itself to sleep. 


    As you must have garnered by now - circadian rhythm is an integral part of your lifestyle. It is the reason that your body falls asleep and wakes up every day. With so much riding on its back, we must ensure that we never purposefully affect circadian rhythm and cause ourselves problems. So, be sure to keep up a healthy life with sufficient sleep in between. 

    And if you do find yourself struggling with any of the sleeping disorders, be sure to follow our tips to get your sleep schedule on track. But remember - if these sleep disorders are prolonged for long, they can have severe repercussions. So, be sure to reach out to a doctor if you ever find yourself in this clutch! 

    This article is for informational purposes and should not replace advice from your doctor or other medical professional.
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    2. Emily Carlson. Resetting Our Clocks: New Details About How the Body Tells Time.


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    4. Junxin Li, PhD, Postdoctoral Research Fellow, Michael V. Vitiello, PhD, Professor, and Nalaka Gooneratne, MD, MSc, Associate Professor. Sleep in Normal Aging.


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