The Circadian Rhythm: What It Is, How It Works, and How to Use It to Your Benefit

Our body’s natural clock is called the Circadian Rhythm, essential in regulating our daily patterns.

Tips:

• Sunlight: get exposure to sunlight early in the morning (5 to 10 minutes) and during the day; always be sun safe.
  
  
• Sunlight Exposure: if possible, get direct sunlight, meaning not through a window, so be outside even just for 5 to 10 minutes and always be sun safe.
  
  

• Work Inside? have a break every hour, or when you can, and go outside for a walk for 5 minutes.

• Prepare for Bed: engage in relaxing activities before bed: Such as reading, meditating, calming music, or taking a warm bath. Warm bath or shower 1 to 2 hours before bed. Avoid caffeine and alcohol several hours before bed.
  
  
• Bedtime & Screens: limit exposure to screens 1 hour before bed; such as Mobile phones, Tablets, TVs, Smartwatches, and other artificial light.
  
  
• Sleeping: be in complete darkness when you sleep.
  
  
• Sleep Pattern: go to bed and wake up at the same time every day, and sleep for about 8 hours.

Understanding the Circadian Rhythm workings can help us better use this rhythm for improved health benefits, better sleeping, and increased productivity levels. Although, disruptions to this rhythm can have health consequences. The best example of this is sleep disorders.

Today, you will learn what the circadian rhythm is, how it works, and what you can do to maximize its benefits to your health.

What is the Circadian Rhythm?

As with most living beings, in humans, the circadian rhythm is a process in the body that acts like a clock whose function is to regulate the proper functioning of other biological processes.

Five primary internal clocks regulate essential cycles in the human body [1]:

• Diurnal (night and day)
• Circadian (24 hours)
• Ultradian (less than 24 hours)
• Infradian/Circalunar (1 month)
• Circannual (1 year)

In turn, these cycles regulate various processes in your body, including the sleep/wake cycle, hormonal activity, body temperature, and eating and digestion functions.

In humans, the circadian rhythm lasts 24 hours and is controlled by biological clocks of protein molecules interacting with the cells that make up your body’s tissues and organs.

At the same time, all these biological clocks are synchronized with a master clock (circadian pacemaker) located in the brain.

This master clock consists of around 20,000 nerve cells (neurons) that form a structure called the suprachiasmatic nucleus (SCN), located in a region of the brain known as the hypothalamus [22].

This master clock is influenced by various factors, both internal and external, but light is the main factor [2].

This is why circadian rhythms are closely linked to the day and night cycle. The sleep-wake cycle is the most obvious example.

When circadian rhythms are working correctly, they promote deep, restful sleep that supports good health.

But when there is some failure in these rhythms, conditions such as insomnia immediately appear, and these conditions can have consequences for your health in the short, medium, and long-term [3].

How does your circadian rhythm work?

The different circadian rhythms coordinate the proper functioning of various physical and mental processes over 24 hours.

Although different internal and external factors influence these rhythms, they ultimately have their origin at the genetic level [3].

In humans, the Period and Cryptochrome genes are responsible for coding proteins that’ll accumulate in the nucleus of cells as night approaches and decrease as the day begins.

These genes are also found in many animals, and some studies indicate that the proteins that these genes encode are precisely those that produce the sensations of wakefulness and sleepiness.

However, the Period and Cryptochrome genes are also influenced by external factors, mainly light [4].

At this point, the master clock or SCN located in the brain plays an essential role.

Cells in the SCN are highly sensitive to light and respond differently depending on the amount of light available in the environment.

Although your skin can also detect changes in the ambient light level [5], these changes are primarily detected by your eyes.

Environmental changes detected by your eyes reach nerve cells in the SCN, which immediately send signals to other parts of your body to make you feel more awake or sleepy.

Your hormones and other factors related to the circadian rhythm

The hormones melatonin and cortisol are integral parts of the circadian rhythm machinery.

While melatonin is a hormone related to inactivity and is responsible for making you feel relaxed and sleepy, cortisol is a hormone that promotes activity and alertness.

Although melatonin and cortisol are the main hormones related to the sleep/wake cycle, other hormones like vasopressin, acetylcholine, insulin and leptin also play an important role [6]:

In addition to hormones, there are other factors that can also influence the circadian rhythm. For example:

Your body temperature drops when you go to sleep and increases when you wake up

Your metabolism decreases during sleeping hours and increases during waking hours

Your body associates physical activity with waking hours, and a lack of physical activity with rest hours.

It is also known that high-stress levels associated with excessive work and other similar factors can increase blood cortisol levels, which can influence circadian rhythms [7].

Patterns and age

Circadian rhythms are not set in stone, and each person’s rhythm can vary according to their “chronotype” and age.

For example, some people feel more energetic at certain times of the day, while their energy levels drop at other times.

This is called a personal chronotype, and it tends to run in families.

Although there may be many small variations in these patterns, in general, there are two major groups of chronotypes:

You are a morning person or early bird when you feel more awake and have higher energy levels in the morning

You are an evening person or night owl when you find it hard to start your day early in the morning but feel higher energy levels at night [8]

Another factor that also influences circadian rhythms is age.

As people age, their circadian rhythms change as well.

For example, newborns don’t usually have a circadian rhythm during their first three months. That’s why their sleep patterns tend to vary at the beginning, which naturally ends up affecting the sleep quality of their parents.

However, after 3-9 months, children’s bodies begin to produce the necessary hormones to regulate their sleep cycle, especially melatonin [9].

On the other hand, teens tend to experience a change in their sleep patterns that allows them to stay awake later at night.

In teens, melatonin levels don’t rise until approximately 11:00 pm. However, their bodies still need to get the same number of sleep hours as younger children (about 9 hours) [10].

While adults are often more prone to variations in their circadian rhythms due to lifestyle pressures (work, family, etc.)

However, a more relaxed lifestyle that maintains a consistent daily routine is often enough for the average adult to maintain a stable circadian rhythm.

If the latter is your case, you should feel tired about an hour or two before midnight and require 7 to 9 hours of sleep each day to feel refreshed when you wake up.

It is essential to understand that all the factors mentioned above don’t act independently but are all part of the same machinery, where all the pieces work together to keep you active during the day and sleepy at night.

Why you should care about suffering disruptions to your circadian rhythm

Various health problems can arise as a consequence of a disturbed circadian rhythm.

This includes minor temporary conditions and chronic illnesses that can last a lifetime.

This happens because regular sleep is essential for your body to carry out various regenerative processes and eliminate waste accumulated during the day in your cells [11].

Naturally, the type and severity of the conditions that may appear as a consequence of an altered circadian rhythm will depend on the characteristics and physical conditions of each individual.

Among the health conditions that can appear in the short term are:

• Low energy levels
• Hormonal problems
• Infertility
• Digestive problems
• Memory failures
• A weakened immune system

Among the health conditions that can appear in the long term are:

• Cardiovascular conditions
• Metabolic conditions
• Skin and hair problems
• Obesity
• Diabetes
• Mental health conditions

On the other hand, some health problems, such as chronic stress, depression, and insomnia, may be related to some circadian rhythm sleep disorders [12, 13].

Circadian rhythm sleep disorders are alterations characterized by a failure in a person’s internal clock to adjust correctly to the normal 24-hour cycle.

These disorders are due to several causes but usually relate to the person’s lifestyle.

Some of the sleep disorders related to a circadian rhythm imbalance include:

• Delayed sleep phase disorder
  This occurs when you go to sleep and wake up a few hours after most people do. This is the most common type of sleep disorder.

• Advanced sleep phase disorder
  This occurs when you go to sleep and wake up a few hours earlier than most people.
  
  
• Jet lag
  Jet lag is a circadian rhythm disorder that occurs if you take a long-distance plane trip that covers five or more time zones. This results in you having trouble sleeping at night or staying awake during the day at your destination.
  
  
• Shift work disorder
  This problem is common among people who routinely have to work at night (shift workers). Shift workers often experience trouble sleeping, tiredness, sudden mood swings, and daytime sleepiness.

What factors can alter your circadian rhythm?

If you have had sleep problems at any point in your life, you may realize how fragile the circadian rhythm is and how easy it is to lose it.

Many factors can cause alterations in circadian rhythms; even a small change in your daily routine could cause these disorders. However, it’s also quite common for a combination of several factors to disrupt circadian rhythms.

• Sleeping extra hours
  Sleeping more hours during the day than your body needs can cause trouble sleeping at night.
  
  
• Air travel
  Going through multiple time zones during air travel can cause your internal clock to have trouble adjusting to the new time at your destination, leading to temporary sleep problems.
  
  
• Excess artificial light
  The blue light that radiates from electronic devices like smartphones, tablets, computer monitors, and even TVs has the same effect on your brain as exposure to sunlight.
  
  
• Night shifts
  It is common for people who work at night regularly to develop shift work disorder, a problem that prevents them from sleeping during the day and night.
  
  
• Not following a consistent sleep schedule
  If you frequently change your bedtime and wake-up hours, your circadian rhythm will likely be out of balance.
  
  
• Excessive exercise at night
  Doing intense exercise a couple of hours before going to bed can stimulate your brain and keep you awake for more hours than usual.
  
  
• Caffeine and alcohol
  Consuming too much caffeine and alcohol on a regular basis, especially around bedtime, can overstimulate your brain and disrupt your circadian rhythm and sleep pattern. Even eating large meals late at night can have the same effect.
  
  
• Stress
  Stress-related to working conditions and lifestyle can significantly increase the risk of suffering from a circadian rhythm disorder. This may be related to increased cortisol levels [2, 14, 15].
  
  

What you can do to maintain a healthy circadian rhythm

If you are suffering from a circadian rhythm disorder and are having sleep issues, there are many steps you can take to try to solve the problem. Here are a series of tips from experts in the field.

• Look for sunlight when waking up
  Your circadian rhythm is regulated by light, so getting a good dose of natural light early in the morning can help you optimize your circadian rhythm.
  
  
• Avoid artificial light before bedtime
  Avoid using electronic devices (smartphones, TVs, computers, etc.) at least 1-2 hours before bedtime. The blue light emitted by screens has the same effect on the brain as sunlight.
  
  
• Establish a regular sleep schedule
  Remember that your brain is like a computer; you can program it differently to do what you need. For example, try to always wake up and go to bed at the same time. That way, you can program your brain to do the same thing automatically.
  
  
• Eliminate noise
  Maintaining a quiet and noise-free environment is essential to falling asleep. If you can’t cut out all the noise in your environment, you have several options to reduce it: a white noise machine, headphones, or insulation for your room.
  
  
• Lower the temperature
  It has been proven that brain activity decreases more easily at bedtime when the room temperature is kept low.
  
  
• Exercise regularly
  Physical exercise has many health benefits, and one of them is helping your body regulate its energy and stress levels more effectively and conveniently, to the point where you’ll improve your ability to fall asleep more easily, although do not do exercise just before you intend to sleep.
  
  
• Avoid consuming substances that affect your nervous system
  Caffeine, alcohol, and tobacco are substances that act in one way or another on your nervous system. If you want to sleep better, you should try to reduce or eliminate their intake, especially before bedtime.
  
  
• Learn how to relax
  Keeping your mind and body free of stress is vital to being able to sleep well. Today, there are many relaxation techniques that you can practice, such as Yoga (24), Mindfulness (23), and visualization (25).

So you have several options to choose the best suits your personality and particular needs.

Final Thoughts

Maintaining a healthy Circadian Rhythm is essential for your body to function correctly, as when the balance of this 24-hour cycle gets disrupted, it can have serious consequences.

Check out our general tips at the start of this article, yet consult your physician if you’re having trouble getting your Circadian Rhythm into sync.

This is something you want to get right, and the earlier in your life the better.

FAQ

• Is it best to sleep in pitch darkness?

  Yes. The human body is highly sensitive to light, and just a small amount of light coming through your eyelids can be enough to disrupt your normal sleep cycle [16].
  
  

• When is the best time to go to sleep?

  Most people may generally find it appropriate for their health to fall asleep at approximately 10:00 pm. However, this is also subject to the characteristics and needs of each individual [17].
  
  

• When is the best time to wake up?

  The best time will depend on the needs of each individual and other factors such as age, level of daily activity, etc. However, in general, the ideal time should match a number between 7-9 hours of sleep each night [18].
  
  

• How many hours of sleep should you get?

  The number of hours an individual should sleep each day is primarily related to their age. Still, as a general rule, the number of hours needed decreases as the individual ages.

  For example, a newborn will need 14-17 hours of sleep, a middle-aged adult will need 7-9 hours, and an older adult 7-8 hours [19, 20].
  
  

• What are some sleep tips?

  Among the main tips that an individual with mild sleep problems can follow are maintaining a regular sleep schedule, reducing the consumption of substances that alter the nervous system, such as caffeine, alcohol, and tobacco, and ultimately, avoiding the use of screens a few hours before bedtime.
  
  

• Can sleep affect your ability to lose weight?

  Not sleeping the necessary number of hours each night can cause your brain to force you to eat more to meet the additional energy demand due to a lack of rest. This can make it difficult to stick to a diet regularly [21].
  
  

• What is the best circadian rhythm?

  The best thing you can do to keep your circadian rhythm optimized is to have a regular sleep routine and a calm, relaxed environment at bedtime, also avoiding light as much as possible.
  
  

• How do I find my circadian rhythm?

  The best way to find your ideal circadian rhythm is to understand your personal chronotype.
  
  

• Do you feel more awake and energetic during the day or at night?

  Answering this question correctly can help you find the most appropriate routine to follow to optimize your circadian rhythm.
  
  

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References:

1. WebMD
What Are Biological Rhythms?
https://www.webmd.com/a-to-z-guides/what-are-biological-rhythms

2. National Institute of General Medical Sciences
Circadian Rhythms
https://nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms.aspx

3. National Library of Medicine
Overview of circadian rhythms
https://pubmed.ncbi.nlm.nih.gov/11584554/

4. Science Direct
The role of clock genes in sleep, stress, and memory
https://www.sciencedirect.com/science/article/pii/S0006295221000897

5. Science Direct
How does the skin sense sunlight? An integrative view of light sensing molecules
https://www.sciencedirect.com/science/article/abs/pii/S1389556721000022

6. National Library of Medicine
The Impact of Sleep and Circadian Disturbance on Hormones and Metabolism
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4377487/

7. National Library of Medicine
Interaction between circadian rhythms and stress
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314421/

8. WebMD
Get in Touch With Your Circadian Rhythm
https://www.webmd.com/sleep-disorders/find-circadian-rhythm

9. National Library of Medicine
Physiology, Circadian Rhythm
https://www.ncbi.nlm.nih.gov/books/NBK519507/

10. UCLA Health
Sleep and Teens
https://www.uclahealth.org/medical-services/sleep-disorders/patient-resources/patient-education/sleep-and-teens

11. Sleep Foundation
Why Do We Need Sleep?
https://www.sleepfoundation.org/how-sleep-works/why-do-we-need-sleep

12. National Library of Medicine
Health implications of disrupted circadian rhythms and the potential for daylight as therapy
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4632990/

13. Harvard Medical School
Why your sleep and wake cycles affect your mood
https://www.health.harvard.edu/blog/why-your-sleep-and-wake-cycles-affect-your-mood-2020051319792

14. National Library of Medicine
Circadian Rhythm Disorders Causes and Risk Factors
https://www.nhlbi.nih.gov/health/circadian-rhythm-disorders/causes

15. WebMD
What Is Cortisol?
https://www.webmd.com/a-to-z-guides/what-is-cortisol

16. National Library of Medicine
Preliminary evidence that light through the eyelids can suppress melatonin and phase shift dim light melatonin onset
https://pubmed.ncbi.nlm.nih.gov/22564396/

17. Cleveland Clinic
When Is the Best Time To Go to Sleep?
https://health.clevelandclinic.org/what-time-should-i-go-to-bed/

18. Medical News Today
What are the best times to sleep and wake up?
https://www.medicalnewstoday.com/articles/best-time-to-sleep-and-wake-up#waking-up

19. Medical News Today
What are the best times to sleep and wake up?
https://www.medicalnewstoday.com/articles/best-time-to-sleep-and-wake-up#by-age

20. National Library of Medicine
Sleeping hours: what is the ideal number, and how does age impact this?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6267703/

21. WebMD
Sleep More, Weigh Less
https://www.webmd.com/diet/sleep-and-weight-loss

22. Centers for Disease Control and Prevention
Circadian Rhythms and Circadian Clock
https://www.cdc.gov/niosh/emres/longhourstraining/clock.html

23. WebMD
What Mindfulness Can Do for You
https://www.webmd.com/balance/guide/what-is-mindfulness

24. National Center for Complementary and Integrative Health
Yoga: What You Need To Know
https://www.nccih.nih.gov/health/yoga-what-you-need-to-know

25. Healthline
5 Visualization Techniques to Add to Your Meditation Practice
https://www.healthline.com/health/visualization-meditation

26. Sleep Foundation
Healthy Sleep Tips
https://www.sleepfoundation.org/sleep-hygiene/healthy-sleep-tips