What are Circadian Rhythms?

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Circadian rhythms follow a 24-hour cycle, which is a part of the body’s internal clock. The clock regulates mental, physical and behavioral changes. These changes respond to light and dark, which affects living things— plants, animals and microbes.

An example of circadian rhythm is the sleep and wake cycle. Not only humans but most organisms on Earth also follow the sleep-wake cycle. Sleeping at night and waking up in the morning, which follows the light and dark circles. The study of circadian rhythms is called chronobiology.

Circadian rhythms are synchronised with a master clock in the brain. Environmental cues influence the master clock.

Circadian rhythms can promote consistent and restorative sleep if properly aligned. However, when the circadian rhythm is affected, it can lead to sleep problems like insomnia. Research also suggests that circadian rhythm regulates physical and mental health.

What are biological clocks?

Biological clocks are naturally present in all organisms and regulate the cycle of the circadian rhythm. The biological clocks are composed of specific molecules like protein, which interact with cells throughout the body. All the organs and tissues contain the biological clock, and researchers have identified similar genes in fruit flies, people, mice, fungi and plants.

These clocks are synchronised with cyclic patterns, which respond to a particular stimulus. The biological clocks that synchronise with circadian rhythms can be endogenous or exogenous.

Endogenous type controls the internal biological clocks— for example- the body temperature cycle. The exogenous type controls the external cue— for example, the sleep and wake cycle.

Other concepts that are related to biological clocks are epigenetic clocks, molecular clocks and senescence. Biological clocks can pertain to female fertility, where fertility gradually decreases from puberty to menopause occurs.

What is the master clock?

The master clock coordinates with all the biological clocks in the body. The master clock is present in the brain and keeps all the clocks in sync.

Animals and humans contain about 20,000 nerve cells form the SNC, which is a part of the brain cells. These nerve cells receive the signals directly through the eyes.

What is the difference between circadian rhythm and circadian clock?

Circadian rhythms are internally driven cycles that rise and fall during the 24-hour cycle. The cycle ensures you sleep at night and wake up in the morning. The master clock in the brain controls and synchronises with these cycles so they work together.

The circadian clock is an internally driven 24-hour cycle that runs for more than 24 hours. However, the clock gets to rest every day after the sun’s light and dark circles.

Some people consume melatonin supplements which contain a mild sleeping effect. The supplements should be consumed at the right time, as they can alter the sleeping cycle.

The internal body clock sets the time for circadian rhythms, which regulate the process like

  • Hormonal activity
  • Sleep and wake cycles
  • Eating and digestion
  • Body temperature rhythm

How Does Circadian Rhythm Work?

The main function of the circadian rhythm is to optimise the body’s process at various points in 24 hours. The word circadian rhythm is derived from a Latin word called “circa diem”— around the day.

All organism that lives on Earth follows a circadian rhythm. Like humans have a sleep and wake cycle, flowers have time for blooming. Likewise, animals stay in their shelter for a particular day— during the day, they can get exposed to predators, so they stay in their shelter.

The digestive system of humans has a particular time to produce proteins, which matches the typical timing of meals and the endocrine system. This will regulate the hormones and regulates energy expenditure.

The circadian rhythm present throughout the body is connected to a master clock which is located in the brain. It is found in the suprachiasmatic nucleus (SCN), part of the hypothalamus. At different times of the day, depending on the rhythm, the hypothalamus sends signals and regulates the body’s functions.

The suprachiasmatic nucleus is sensitive to light. It serves as the critical external cue which influences the signal sent by SCN to coordinate with the internal clocks in the body.

However, other external cues like social activity, exercise and temperature can affect the master clock to some extent, but light has the most powerful influence on the circadian rhythm.

Does the body make and keep its own circadian rhythms?

The human body makes its own circadian rhythm and also maintains it. After a long day, you tend to sleep. The energy expenditure and the rest required for the body will be regulated by the body’s circadian rhythm, which makes you fall asleep.

Genes like Period and Cryptochrome play an important role in the process. These genes code for the proteins that build up during the night and lessen during the day. However, the body’s circadian rhythm will be affected by environmental factors.

How do circadian rhythms affect health?

All the clocks in our body are connected to the master clock in the brain. The internal clock controls the various body functions, and if the circadian rhythm is disrupted, it can lead to various health issues.

The sleep-wake cycle is important as it regulates the physiological processes that help produce hormones, digestion and activation of the immune system. For example, the digestive system contains its own circadian rhythm, which releases hormones and makes us hungry. After consuming food, other hormones will be released that help break down and digest the food. This process slows down when you sleep.

When we eat late in the day, digestion of food will be difficult as the hormones that help with digestion will have a tough time regulating the blood sugar levels after food consumption.

Over time, this type of practice can lead to obesity and Diabetes. If the circadian rhythm within cells get disrupted, it can lead to cancer cell formation.

What factors can change circadian rhythms?

Circadian rhythms can get altered due to certain body and environmental factors. It can get disrupted due to the light-dark cycle, which can make the cycle become out of sync. Other factors include

  • Mutation in genes that affects the biological clocks.
  • Changes in shift work can affect the light-dark cycle.
  • Biological clocks can get disrupted by the light from electronic devices.

These changes in factors can cause sleep disorders and can lead to the development of other chronic health conditions like diabetes, obesity, depression, seasonal affective disorder and bipolar disorder.

How are circadian rhythms related to jet lag?

The biological clocks will work depending on the time zone you live in. For example, if you live in India and fly to Singapore, you will be lagging three hours in time. The lag is because your biological clock will take time to reset to the new time zone. The brain usually takes a few days to adjust to the new time zone.

How To Maintain a Healthy Circadian Rhythm

Circadian rhythm can be maintained with certain simple habits. Maintain a bedtime, and if possible, try to follow the time. Make sure you sleep for 8 hours and keep an alarm to wake you. The body will take some time to adjust, and once the circadian rhythm sets its time, the body will automatically wake up on time.

The sleep schedule should include your weekdays. If there is a disruption in sleep time, you will have to start again. Light is also one of the factors that can cause disrupted sleep. So make sure you sleep in a dark room. Additionally, limit your exposure to mobile phones and laptops. The light can interfere with the sleep cycle and lead to disruption in the sleep cycle.

Other ways to maintain a healthy circadian rhythm

  • Avoid caffeine consumption late in the day.
  • Try taking small naps in the afternoon if required.
  • Avoid heavy meals at night
  • Listen to light music before bed and keep your activities simple.

With the influence of technology, most of us have a hard time sleeping. There are many teas available to calm you down and will help you sleep well. However, consult your doctor if you plan to take products containing active ingredients.


All organisms contain a circadian rhythm, which regulates their sleep and wake cycle. It is a natural cycle of the body, and the process continues every day.

Circadian rhythm can be disrupted due to external factors. This can lead to certain health issues like insomnia and Diabetes. Sleeping in the dark is also recommended to maintain a healthy circadian rhythm. Consult your doctor if there is sleep disruption. Melatonin supplements can help with sleep issues.


The Information including but not limited to text, graphics, images and other material contained on this blog are intended for education and awareness only. No material on this blog is intended to be a substitute for professional medical help including diagnosis or treatment. It is always advisable to consult medical professional before relying on the content. Neither the Author nor Star Health and Allied Insurance Co. Ltd accepts any responsibility for any potential risk to any visitor/reader.

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