What is Circadian Rhythm and how it works

The circadian rhythm is a part of the body’s internal clock, measured in 24-hour cycles. It is widely observed in humans, plants, animals, bacteria and fungi.

The process known as sleep-wake cycle is considered the most important one. The sleep-wake cycle repeats on each rotation of the Earth. These rhythms are driven by the circadian clock, a biochemical oscillator synchronized with solar time.

In this article we will discuss the circadian rhythm in-depth: its functions, the most common conditions that throw it out of sync and how to balance the internal master clock with sleep schedule, healthy routine, circadian rhythm light therapy and more.

Let’s get started.



Age and Sleep

Circadian rhythm is different in babies, teens and adults. Newborn babies don’t have a circadian rhythm up until the time they are a few months old and you guessed it, parents know this all too well. Their circadian rhythm develops as they adjust to the environment. Around 3 months old, their bodies start to produce melatonin and the hormone known as cortisol is developed between 2-9 months old.

Teenagers experience Sleep Phase Delay, a disorder in which sleep is delayed by a few hours beyond the conventional bedtime. Their peak sleepy hours shift to 3 AM – 7 AM, which consequently moves their waking hour to later in the morning.

As for adults, their circadian rhythm should be consistent and stable. Easier said than done but a few lifestyle adjustments can balance the sleep-wake cycle and bring it to optimum levels.


How it gets out of sync

Circadian Ryttm How it gets out of sync

The circadian clock in healthy adults automatically resets every 24 hours. It is fairly easy to throw the circadian rhythm off-balance and here are a few examples of how it gets out of sync:


Nightshifts and work shift with erratic hours can affect the internal clock and circadian rhythm. Shift Work Sleep Disorder is a condition that affects people that work night shifts and rotating shifts.

Travel across time zones

Long distance plane travel can contribute to jet-lag. Jet-lag is a misalignment of the body’s internal clock with the local time at the destination. It usually occurs when flying across three or more time zones. Jet lag is characterized by sleeping problems, impaired thinking, fatigue, daytime sleepiness and emotional difficulties.

Delayed sleep phase syndrome (DSPS)

Delayed sleep phase syndrome is a disorder most commonly affecting the “night owls”. People with DSPS tend to fall asleep later at night and have a hard time waking up early in the morning. This condition is common in teenagers and young adults. Advanced sleep phase syndrome is a condition where a person might fall asleep between 6 and 9 PM and wake up between 1-5 am.

Non-24-hour sleep-wake disorder

Non-24-hour sleep-wake disorder affects blind people as their circadian rhythm is free-running due to the loss of photic input to the circadian clock. It can also affect sighted people with bipolar disorder, brain injury and mental health issues.


Many drugs can interact with the circadian clock and the most common ones include sleeping pills, antidepressants, statins and glucocorticoids.


Stress response is closely affected by the internal body clock. Heightened stress levels can throw the circadian rhythm off-balance, contribute to insomnia and other sleep problems, increase the risk of cardiovascular disease and disrupt the wake-sleep cycle.

Mental health conditions

Certain mental health conditions can contribute to sleep problems and the most common include Attention Deficit Hyperactivity Disorder (ADHD), anxiety, depression and bipolar disorder.

Poor sleep habits

Poor sleep habits such as sleeping at odd hours, long naps or napping late in the evening, eating too close to bedtime, drinking coffee in the evening, excessive screen-time especially before going to bed and working-out late at night can contribute to an unhealthy sleep-wake cycle.


Anatomy of Sleep

Sleep is vital to our overall health and our bodies undergo a series of changes when we sleep. The brain and body slow down during sleep and go through different processes of recovery. The brain stem starts producing a brain chemical called GABA, which reduces the activity of arousal centers in the hypothalamus. Except during REM sleep, the thalamus becomes quiet, letting the body tune out the external world. The pineal gland increases the production of melatonin, a hormone that makes you fall asleep. The amygdala, which is involved in processing emotions, becomes active during the REM stages.

The complexity of sleep involves many other processes which are part of the sleep stages. There are four stages of sleep which are further broken down into two categories – REM and non-REM.

Stage 1 – the transitioning into sleep stage

Stage 2 – the mind and body begin to slow down and it is easiest to be awoken during the first 2 stages.

Stage 3 – known as deep sleep. Breathing, heartrate and brain activity slow down and the body undergoes deep recovery.

Stage 4 also known as REM sleep. During REM sleep the brain is active, similarly to when we’re awake. This phase is also associated with vivid dreaming.

Each cycle lasts between 70 and 120 minutes. The majority of non-REM happens during the first half of the night and is intertwined with REM sleep which first occurs within 90 minutes of falling asleep. This progression of sleep stages is also known as sleep architecture, cool right?

Every part of the body experiences notable change during sleep.

Breathing slows down during non-REM stages, most notably during the 3rd stage of deep sleep. Breathing rates increase during the REM stage.

Heart rate follows the same pattern as breathing, it slows down during the first 3 stages of sleep and increases in the 4th stage.

Brain activity also slows down during the first stage but it accelerates during phase 2 and 3. Brain activity is accelerated during the REM sleep and this is the phase where we experience vivid dreams. REM stage is vital to brain restoration as it helps facilitate proper brain function.

Hormone levels are closely tied to our sleep cycles. Getting proper sleep is vital to numerous hormones including:

Melatonin – a hormone which helps promote sleep.

Growth hormone – supports metabolism and bone and muscle development.

Cortisol – also known as the fight or flight hormone, it is a vital part of the body’s stress response system.

Leptin and ghrelin are hormones that help control and maintain appetite. Ghrelin is responsible for regulating our appetite and leptin is a neurotransmitter that signals fullness.


Organ Body Clock

Every organ has a maintenance and repair schedule on a daily basis. Traditional Chinese Medicine has a 24-hour body clock, divided into 12 two-hour intervals. Each interval corresponds to a different body organ. The clock follows the cyclical ebb and flow of energy and is often used for determining various diseases. Qi (Chinese for energy) is present everywhere and is in a constant state of flux, constantly moving within the body, between people and objects. The body clock is built on the concept of qi and knowing the specific times of bodily functions can help regulate the sleep-wake cycle. Read on to learn more about specific times and their relation to body organs.

5 AM -7 AM – Large intestine – this is the perfect time to wake up, have a bowel movement, take a shower, meditate and set the tone for the day.

7 AM – 9 AM – Stomach – it is a great time for a nutritious breakfast, brisk walk or work that requires good concentration.

9 AM -11 AM – Spleen and Pancreas – The spleen and pancreas produce enzymes which help digest food and release energy. This is the ideal time for focused work or exercise.

11 AM – 1 PM – Heart – this is the best time to eat lunch, have a cup of tea or a short nap.

1 PM – 3 PM – Small Intestine – digestion is complete and this is a good time for study or exercise. 

3 PM – 5 PM – Bladder – this is the time to study, work or complete brain-challenging games. It is recommended to hydrate during this time to help move waste into the kidney’s filtration system.

5 PM – 7 PM – Kidneys – this is the perfect time for a walk, massage, gentle stretching and dinner.

7 PM – 9 PM – Pericardium and Circulation – this is the perfect time for light mental activities such as reading.

9 PM – 11 PM – Triple Burner/Endocrine system – this is the perfect time for sleeping and conserving energy.

11 PM – 1 AM – Gallbladder – at this time, it is vital to be asleep as the yin energy fades and yang energy begins to grow.

1 AM – 3 AM – Liver – this is the time for deep sleep and deep detox and restoration. Toxins are released from the body and fresh new blood is made.

3 AM – 5 AM – Lungs – the body should still be asleep but if you find yourself awake during this time, it is best to do gentle pranayama or breathing exercises.


Circadian rhythm light therapy

Circadian light therapy, also known as bright light therapy, heliotherapy or phototherapy, is the exposure to natural daylight or an alternative form of light such as a lamp. Light therapy is used to reset the circadian rhythm and as a treatment for Delayed Sleep Phase Syndrome. It is often a great treatment for seasonal affective disorder (SAD) which is a mood disorder that happens around the same time of year i.e., exhibiting depressive symptoms during wintertime or heightened anxiety during summertime. The cause of SAD is usually low exposure to sunlight during the short days of winter.

Blue light therapy is most commonly used as a treatment for skin conditions such as sun damage, acne, enlarged oil glands and scars. It can also aid in the treatment of depression, especially during the darker winter days. Exposure to bright light therapy lamps can significantly reduce feelings of depression and anxiety and balance the natural sleep-wake cycle, especially during winter time when sunlight is scarce.  


Health effects of an unbalanced circadian rhythm

A circadian rhythm that is out of sync for a prolonged period of time can wreak havoc on both your mental and physical health. It can contribute to cognitive decline, weight gain, circulatory and heart problems, memory deficits and more. You may experience adverse health consequences including:

Immune dysregulation

The circadian rhythm is closely tied to our immune system. When the sleep-wake cycle is disrupted, so is our body’s response to various diseases. This is closely tied to the production of hormones, which regulate pretty much everything in our body. Lack or high-quality sleep can significantly reduce the body’s defensive mechanisms.

Mood disorders

We all know that cranky and depressive feeling when we haven’t had enough sleep. Not getting enough sleep or having a sleep cycle that is not in synergy with the sunlight can significantly influence your mental health and well-being. This in turn can lead to depression, anxiety, heightened stress response and other mood disorders.

Memory and learning deficits

Good night’s sleep is essential for memory retention. The brain will start lagging if it’s exposed to prolonged periods of disrupted sleep schedule. Analysis of sleep data shows a correlation between cognitive decline and sleep problems. Memory and learning issues have been related to a circadian rhythm that is thrown off balance.


Insomnia is the most common sleep disorder. Insomnia is a disorder where people experience trouble falling and/or staying asleep. This condition is also characterized by daytime sleepiness, low energy levels, depressed mood, cognitive decline, irritability and psychological stress. Risk factors include chronic pain, psychological issues, menopause, certain medications and excessive intake of drugs, caffeine, nicotine and alcohol.

Reproductive problems

Recent studies clearly show the correlation between an unbalanced circadian rhythm and reproductive issues. Disruption of the circadian rhythm can lead to poor fertility, altered hormonal levels and increased rates of miscarriage.

Chronic fatigue

Chronic fatigue also known as Myalgic Encephalomyelitis is a systemic neuroimmune condition characterized by severe disabling fatigue, lasting more than 6 months. Irregular sleep patterns and a lifestyle that lacks routine can contribute to the development of chronic fatigue syndrome.

High blood pressure

Blood pressure is driven by our internal biological clock and is modulated over a 24-hour cycle. Blood pressure levels are closely related to the sleep-wake cycle. Poor sleep, lack of physical activity and high stress levels can contribute to high blood pressure.

Weight gain

One of the side effects of poor sleep is weight gain and increased body mass index, which can lead to further health issues such as type 2 diabetes and coronary artery disease. The dysregulation of the neurotransmitters ghrelin and leptin, which are responsible for promoting hunger and feeling full, can lead to an increased appetite.


Drowsiness is closely related to light exposure and circadian rhythm. Crash occurrence analysis shows most accidents happen during night time (between 2 and 5 am) as lack of light contributes to low alertness and slow reflexes.


How to balance your circadian rhythm?

Spend time in natural light

Spending time in natural light, especially in the morning, is a great way to reset and balance your internal clock. Going for a brisk walk or a jog in the morning are great ways to spend time outdoors. Exposure to daylight is essential to keeping the circadian rhythm in balance at all times. 

Bright light therapy

Bright light therapy is a great substitute for natural light. It is especially helpful during the shorter and colder winter days. Light therapy affects brain chemicals responsible for mood and sleep and is a great way to ease seasonal affective disorder (SAD). Bright light therapy lamps are inexpensive yet they provide a plethora of benefits.

Follow a routine

Еstablishing a routine is essential to resetting and balancing the circadian rhythm. One way to build a healthy routine is to go to bed and wake up at the same time each day. Adjusting the sleeping schedule should be done in 30-mintue window of change, meaning if you usually go to bed at around midnight – 11.30 would be your new bedtime. Once your body adjusts to 11.30, you can change it to 11 and so forth.

Get moving

Exercise plays a major role in improving our sleep quality and duration. In turn, a healthy sleep-wake cycle improves our strength and performance. Timing is also important when incorporating regular exercise, as breaking a sweat too close to bedtime can actually throw your internal clock off rhythm. It is best to avoid working out 2 hours prior to going to bed.


Meditation is an ancient practice of mindfulness and a technique used for training attention and awareness. Practices vary between traditions but the goal of meditation remains the same: reduced stress, enhanced sense of well-being, improved awareness and perception. Meditation can be really helpful both in the morning and right before going to bed. Practiced in the morning it helps to set the tone for the day and it is a great way to reset and unwind before going to bed.

Avoid late naps

Naps are fine as long as their timing is right. Experts recommend napping right after lunch (which should be around noon) and no later than 2 PM. Napping after 2 PM may affect your ability to fall asleep and disrupt your sleep-wake cycle. Another thing to remember is to keep you naps short – up to 30 mins.

Time your caffeine intake

Caffeine is truly the nectar of the gods but timing your coffee intake is essential if you want to get a good night’s sleep. Coffee is an energy booster therefore it is best consumed in the morning. Avoid coffee at least 6-8 hours before going to bed as caffeine has a half life of 5 hours, meaning it takes an average of 5 hours for the body to eliminate half the amount consumed.

Limit screen time

Avoiding screen time and bright light at night is necessary for keeping the internal clock on point. Phones, TV, laptops and iPads activate the brain and lead to poor sleep. Reading a book before bedtime is a great way to unwind and prepare the mind and body for a restful sleep.

Regular meal time

Eating at regular intervals can have an immense effect on your circadian rhythm and sleep-wake cycle. Eating too close to bedtime can contribute to indigestion, acid reflux, problems falling and staying asleep. According to the Chinese Body Clock, the largest meal should be around noon, as our digestion is strongest during that time. Incorporate regular meal times and avoid eating anything at least 2 hours before going to bed.

Sleep in a supportive environment

Sleeping in an environment that is peaceful, clean, clutter-free and dark is essential for a good, restful sleep. Change your bed sheets every week, keep your bedroom clutter-free, throw away your TV (in general avoid spending time in front of any screen in the bedroom), and make sure your bedroom is as peaceful as it can be.


Melatonin is a hormone naturally present in our bodies. It is released by the pineal gland at night and it plays a role in maintaining the sleep-wake cycle. Melatonin supplements are a great way to help ease insomnia, delayed sleep phase and jet-lag. Although it is unlikely to become dependent, melatonin should be used only for a short amount of time.


Natural rhythms are ever-present and they guide and dictate everything we do. Our breath and heartbeat are nature’s reminder of its pulsing rhythm. Women experience it through their monthly cycles, the moon’s phases guide the ebb and flow of the oceans and seas, the sun rises and sets, the seasons change in a cyclical and rhythmic manner and our internal rhythm is always connected to nature. Following these natural (external and internal) rhythms is an essential part of a fulfilling, healthy and happy life. We invite you to drop us a message if you would like to receive more tips on how to maintain a healthy sleep-wake schedule. We would also love to know how you maintain your inner master clock, feel free to share your thoughts with us in the comments down below.

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