Everything You Need To Know About Circadian Rhythm

circadian rhythm

If you are a health buff, you might have often come across the term ‘Circadian Rhythm’ while carrying out research and reading online articles. You might be confused about what exactly does it mean and how does it function. To help you with this, here is a one-stop station of everything you need to know about circadian rhythm.

What Is Circadian Rhythm?

The circadian rhythm is a collection of physical and mental changes that follow a 24-hour cycle, and are a part of the body’s internal clock. These rhythms are equipped to respond to changes in your environment, particularly those associated with light and darkness.

This rhythm in the behavioral patterns and physiological processes are observed in all living beings, including plants, animals, microorganisms, and even cyanobacteria. The body systems are set according to these rhythms which have been synchronized with the master clock in the brain.

It is endogenously generated, but can often be regulated by environmental cues such as light and temperature. Hence, we notice a direct link between our body cycle and the phenomena of day and night. Linked patterns of brain wave activity, cell regeneration, hormone production, and other biological processes to this rhythm have been found.

Are Biological Clocks And Circadian Rhythms The Same?

While there is a prominent correlation between biological clocks and circadian rhythms, they are actually not the same thing. Biological clocks are the body’s innate timing mechanism, which is essential for the regulation of all bodily processes, including circadian rhythms.

Biological clocks are deemed to be present in every tissue and organ, in several organisms. They are composed of specific protein molecules and are responsible for the proper maintenance of the cells in the body. It is these clocks that actually generate circadian rhythms and maintain their timings.

In conclusion, we can say that the circadian rhythms are a consequence of the biological clocks. However, you should know that not all biological clocks are circadian. The changes within an organism as a result of altering seasons are due to biological clocks that do not follow a 24-hour cycle. Hence, circadian rhythms are biological clocks but not all biological clocks are circadian rhythms.

How Does The Circadian Rhythm Work?

The circadian rhythms are designed to function in sync with the state of your body, to some extent. A particular bodily process tends to occur more at a time it would be carried out best, within the 24-hour time duration. These rhythms are present in all organisms and are adjusted to work around the day. In fact, the etymology of the word circadian suggests its Latin origin- ‘circa diem’ – meaning around the day.

Circadian rhythms establish a link between your physical and mental systems, which are connected to a master clock, or the circadian pacemaker. A circadian pacemaker is a small group of nerve cells located in the suprachiasmatic nucleus (SCN), in the hypothalamus.

The SCN is highly sensitive to light which makes it a critical environmental cue to the circadian rhythm. It controls the circadian cycles and also influences many other physiological and behavioral rhythms occurring over a 24-hour period, which includes the sleep/wake cycle.

Clock genes in the SCN transmit signals at fixed times of the day to maintain the functioning of the body. These signals have a crucial role in the coordination of the various internal clocks in the body. Many other external cues apart from light, like temperature, exercise, and social interactions also have an influence on the circadian rhythms.

What Is The Relationship Between Circadian Rhythm And Sleep?

Circadian rhythm is usually used by people in the context of sleep. This is because these rhythms are what determine your sleep patterns. The sleep-wake cycle is one of the most acclaimed and well-known examples of the circadian rhythm.

The SCN is what controls the production and secretion of melatonin (the sleep hormone which is essential for quality sleep), which decreases in the presence of light. Hence, more of this hormone is produced at night (in less light), and lesser during the day. Exposure to screens and UV light at night thus causes a modification in your circadian rhythm and alters your sleep cycle.

Hence, the circadian rhythm aligns the body’s sleep cycle to match nature’s phenomena of day and night. This establishes a constant cycle of rest and alertness in the body which enhances productivity during the day and allows the body to rejuvenate at night.

Is Circadian Rhythm Universal?

1. Life – Night

Night-time has often been associated with life. This is actually true, as animals have evolved over the years to align hormone timings such that instances of labor and birth are triggered at night.

This is credited to be an attempt to safeguard the mother and her new-born, who will be less exposed to predators at night. Even in humans, it has been observed that more natural deliveries occur after midnight than during the afternoon.

2. Death – Morning

It has been noticed that most deaths occur during the time between 8:00 a.m. and noon. Even cases of heart attacks, strokes, and other fatal health accidents are more common then. This can be attributed to the circadian rhythm and the link between mornings and death.

Our blood pressure reaches its lowest at around 3:00 a.m. When the body clock awakens (with the rising sun at dawn) and we wake up from our night slumber, this blood pressure level increases sharply. As a result, one becomes susceptible to instances like stroke during this time.

3. Asthma – Dawn

Cases of asthma are mostly recorded at dawn, probably due to the low cortisol levels in the body during that time. Cortisol is the primary stress hormone, which increases glucose content in the bloodstream. It is an anti-inflammatory steroid.

Cortisol production reaches its daily low during this time. This is essential to increase the response of the β-adrenergic receptor in the respiratory tract smooth muscle. Eventually, reducing airway hyperresponsiveness in patients with asthma.

How To Maintain A Healthy Circadian Rhythm?

As the circadian rhythm is closely linked to many body processes like cognition, coordination, and immune function, it becomes imperative that you pay close attention to it. Here are some tips that you can follow in order to maintain a healthy circadian rhythm and consequently benefit your overall health:

  • Maintain a proper sleep schedule of 7-9 hours at night
  • Get sunlight in the morning
  • Avoid afternoon naps and sleeping during the day
  • Limit screen usage at night


Circadian rhythms play vital roles in the regulation of various physiological processes, such as hormone secretion, sleep-wake cycles, and immune regulation. They are mostly affected by light and darkness and are controlled by the brain. They have a direct impact on one’s sleep, body temperature, hormones, appetite, and other body functions, and are closely related to the body clock.


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