How Does Circadian Rhythm Affect Humans?
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Circadian Rhythm - The Sleep-Wake Cycle

Written by
Dr. Akanksha
and medically reviewed by Dr. J N Naidu

Published on Nov 04, 2022   -  4 min read


Circadian rhythm is a 24-hour cycle of the body that is necessary to carry out important functions and processes. Read the article to know about it in detail.


Sleep regulation is processed by the homeostatic physiology of the circadian rhythm. Circadian rhythm is a 24-hour clock in the brain that regulates cycles of alertness and sleepiness in response to light changes in the environment. The word circadian comes from the Latin phrase ‘circa diem’ which means ‘around a day.’ Human behavior and physiology are shaped by the earth’s rotation around its axis. The biological circadian rhythm helps humans to adapt to changes in the environment and prepare for changes in temperature, radiation, and food availability.

What Is Circadian Rhythm?

Circadian rhythm is the behavioral, physical, and mental changes that follow a 24-hour cycle. These natural processes react to light and dark and affect almost all living beings, including animals, plants, and microbes. One of the important circadian rhythms is the sleep-wake cycle. The study of circadian rhythm is called chronobiology. Various systems of the body follow circadian rhythms that are in sync with the master clock of the brain. The master clock in the brain coordinates biological clocks in living beings, keeping the clocks synchronized.

A normal and properly aligned circadian rhythm contributes to consistent and restorative sleep. When the sleep is disrupted and thrown off, it may result in significant sleeping issues such as insomnia. Without a proper circadian rhythm, a person may face difficulties falling asleep, waking up during the night, and cannot sleep as long as they wish to in the morning. It may also cause reduced total sleep and fragmented, shallower, and poor-quality sleep. Studies also show that it plays an important role in various aspects of mental and physical health.

Is Circadian Rhythm the Same as a Biological Clock?

The biological clock is the natural timing device of the organism regulating the circadian rhythm cycle. It helps to regulate the timing of bodily processes. They contain specific proteins that interact with cells throughout the body. Almost every tissue and organ have biological clocks. A circadian rhythm is an effect of the biological clock, and not all biological clocks are circadian rhythms. For example, animals adjust to changing seasons using their biological clock with timing that is different from a 24-hour cycle.

How Does the Circadian Rhythm Develop in Humans?

The circadian rhythm develops postnatally in mammals. When in the womb, the fetus is not exposed to the external environment; hence, neonates are born with an immature and weak functioning system. The 24-hour circadian rhythm development occurs during the first four months of life as, during this time, the newborn experiences physiological changes and adapts to the environment. Core body temperature is the most tightly regulated system, and any deviations show the establishment of a circadian rhythm. Some minimal deviations occur in the womb, but the perception of the difference between day and night begins in the first weeks of life. Melatonin, a hormone critical to the development of circadian rhythm, emerges around three months of age. The production of cortisol, a hormone important for the proper functioning of the circadian rhythm, happens as early as eight weeks up to nine months of age. Since infants experience quick physiological changes after birth, deviations in core body temperature and production of cortisol and melatonin allow newborns to establish a stable circadian rhythm.

How Does Circadian Rhythm Affect Health?

Most people experience the effect of circadian rhythms on their sleep cycle and pattern. The sleep-wake cycle is one of the most critical examples of the relevance of circadian rhythm. Light exposure during the day causes the master clock to send signals that process alertness and helps keep a person awake and active. As night falls, the master clock stimulates the production of melatonin, the sleep hormone promoting sleep, and keeps transmitting the signals to help stay asleep throughout the night. This is how the circadian rhythm aligns sleep and wakefulness during the day and night to have a stable cycle of restorative rest, enabling increased daytime activity.

Circadian rhythm plays a vital role in almost all systems of the body. It influences other important functions of the body, such as:

  • Hormone release.

  • Body temperature.

  • Eating habits, weight, and digestion.

  • Mental health, including the risk of depression, bipolar disorder, dementia, etc.

  • Immune system and processes of DNA (deoxyribonucleic acid) repair.

  • Some studies also indicate that the circadian rhythm can also affect the effectiveness of anti-cancer drugs and that new medicines can make the biological clocks kill cancer cells.

What Are the Factors That Disrupt Circadian Rhythm?

Any change in the body and environmental factors may cause the circadian rhythm and the light-dark cycle to be out of sync. The changes can lead to sleep disorders and may also cause chronic health problems such as bipolar disorders, depression, obesity, diabetes, and seasonal affective disorder. Some changes can be:

  • Light from electronic gadgets during the night can affect the circadian rhythm. The blue light from electronic devices suppresses melatonin, disturbing sleep.

  • Changes or mutations in some genes can affect the circadian rhythm.

  • Jet lag or working night shifts can cause changes in the circadian rhythm.

How to Maintain a Normal and Healthy Circadian Rhythm?

Some of the healthy tips that can help to improve circadian rhythm include:

  • Get Daily Exercise - Some physical activity during the day supports the internal clock and makes it easier to fall asleep at night.

  • Limit Light Before Bed - The blue light from electronic devices and artificial lights can interfere with the sleep cycle. Try dimming the lights and keeping electronic devices away to improve the sleep cycle.

  • Avoid Caffeine - Caffeine acts as a stimulant to keep a person awake and throw off balance between sleep and wakefulness. Avoiding caffeine is especially advised for those having trouble sleeping, as everybody is different, and some having caffeine may not have problems with sleep.

  • Seek Out Sun - Exposure to sunlight, especially early in the morning, helps improve the circadian rhythm.

  • Keep Midday Naps Short and Early - Long and late naps can push the bedtime and throw the sleep schedule off kilter.

  • Follow a Consistent Sleep Schedule - Having a varying bedtime or morning wake-up time can interfere with the body’s ability to adjust to a stable circadian rhythm.


A proper understanding of what ticks the biological clock may lead to the management of jet lag, obesity, sleeping disorder, mental health disorder, and other associated health conditions. It can also help people in adjusting to night-time shift work.

Frequently Asked Questions


Is the Sleep-Wake Cycle Similar to the Circadian Rhythm?

The homeostatic physiology of the circadian rhythm, the sleep cycle, or the wake cycle regulates the sleep cycle. The 24-hour internal clock (body clock) in our brain that controls cycles of alertness and drowsiness by reacting to light variations in our surroundings is known as the circadian rhythm.


What Occurs Throughout the Sleep-Wake Cycle?

Melatonin levels in the blood rise in the evening and peak in the early morning. Melatonin is said to improve sleep. When exposed to more light, for instance, when the sun rises, the body produces a hormone known as cortisol. Cortisol is a hormone that naturally encourages the body to gain consciousness.


Why I Am Often Aroused at 3 Am?

There might be various reasons why people wake up at 3 a.m. or some other time and can't get back to sleep. Lighter sleep cycles, stress, or underlying health concerns are examples. Waking up at  3 a.m. may be sporadic and unimportant, but recurring nights like this might indicate insomnia.


Name Some Examples of a Circadian Rhythm Sleep or Wake Disorder?

Some examples of circadian rhythm disorders are advanced or delayed sleep-wake phase disorder, irregular or non–24-hour sleep-wake rhythm disorder, and shift work or jet lag disorder.


How Do I Rearrange My Circadian Rhythm?

Maintaining a regular sleep routine will enable resetting the circadian rhythm. The body will adjust to the new rhythm if you go to bed and wake up simultaneously each day.


What Regulates the Sleep-Wake Cycle?

The central circadian clock in the brain indicates when it is time for sleep. Other circadian clocks are present in the other organs of the body.  The body's internal clocks are in harmony with biological and environmental factors. Light, darkness, and other indicators can assist you in determining when to be awake and when to fall asleep.


How Can I Alter My Sleep-Wake Cycle?

- Try to get up at the same time every day.
- Go to bed at the same time every day.
- Avoid taking alcoholic or caffeine-containing beverages in the evening.
- Avoid consuming large meals at least two hours before bedtime.


What Disturbs Your Circadian Rhythm?

Our circadian rhythms can be disturbed by artificial light, blue light from devices, noise from busy streets, caffeine, stress, and alcohol. In addition, physiological variables like genes and hormones might interfere with the circadian rhythm.


Which Is the Prevalent Circadian Rhythm Disorder?

The most common circadian rhythm disorder is delayed sleep-wake phase disorder (DSWPD). Patients with DSWPD can need help falling asleep on time and staying up until the morning, which interferes with working studies and social responsibilities. The patient may get too little sleep, which might cause fatigue during the day.


How Do I Discover My Natural Circadian Rhythm?

The natural circadian rhythm can be discovered by not setting the alarm for a few weeks and by paying attention to the body's natural wake time. Go camping on the weekend and substitute the bedside lamp with the natural pattern of sunlight.


What Diet Helps Circadian Rhythm?

Having a variety of proteins, rich-fiber foods, and high-quality carbohydrates at breakfast, lunch, and dinner is crucial for satiety and brain fuel. Avoid as much intake of alcohol and caffeine as possible, both of which are brain stimulants.


How Does a Healthy Circadian Rhythm Appear?

If adults maintain healthy habits, their circadian rhythms should be rather stable. If they maintain a routine and seek 7 to 9 hours of sleep per night, their bedtimes and wake times should remain constant. Due to the release of melatonin in adults' bodies, sleepiness usually sets in well before midnight.


At What Time Do Humans Wake Up Naturally?

Most people wake up around 7-9 a.m. A typical circadian rhythm is where peak alertness is around 2-3 hours after awakening and 8-9 hours after awakening, and one gets tired at 3 AM.


What Are the Ways to Educate My Brain to Wake Up?

- Adopt a sleep schedule.
- Simplify the sleep schedule.
- To avoid pressing the snooze button, keep the alarm off.
- Eat healthy food.
- Do some regular workouts.
- Cherish the daylight.
- Conduct a sleep study.
- Treat a sleeping problem.

Last reviewed at:
04 Nov 2022  -  4 min read




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