What Is Circadian Rhythm?

What Is Circadian Rhythm

While you won’t hear it tick, the human body has its own timekeeping system called the circadian clock. This internal clock regulates your body’s natural circadian rhythm (daily cycles of wakefulness and sleep), hormonal activities, body temperature, and other bodily processes. It is guided by environmental cues, such as light, which is why these rhythms are tied to the day and night cycle.

Although the circadian rhythms control virtually all the body processes, several issues can throw them out of sync, leading to sleep disruptions and causing problems with your health. To improve your sleep quality, it’s wise to know how your biological clock works, factors that might throw it off, and how you can maintain a healthy circadian rhythm.

This article will explore everything you need to know about the circadian rhythm in great detail. To learn more about the biological clock and how it influences sleep, read on.

What It Is

According to the National Institute of General Medical Sciences, circadian rhythms are physical, behavioral, and mental processes that take place throughout every day. These natural processes follow a 24-hour cycle and respond mainly to light and dark. They also affect most living things, including plants, animals, and even microbes.

One of the most vital and widely recognized circadian rhythms in humans is the sleep-wake cycle. Others include:

  • Immune function
  • Digestion
  • Body temperature
  • Hormonal activity

Human beings tend to feel more awake as the sun rises and become tired at night. This 24-hour pattern is what many individuals refer to when they mention the circadian rhythm. However, different body systems follow circadian rhythms controlled by the body's clock, which is located in the brain.

How the Body’s Natural Circadian Rhythm Works

Circadian rhythms are essential processes that ensure the body systems are optimized during 24 hours. They’re present in all types of organisms. For instance, they enable flowers in plants to open and close at the appropriate time and protect nocturnal animals from predators by preventing them from leaving their habitats during the day.

In humans, these rhythms are linked to a master clock, also known as the circadian pacemaker. About 20,000 nerve cells make up the circadian clock, a part of your brain known as the suprachiasmatic nucleus (SCN). This structure sits in a specific area in your brain (hypothalamus) and controls your circadian rhythms.

The SCN is very sensitive to light, which acts as an important external cue that impacts the signals sent to coordinate circadian clocks in your body. As your eyes perceive bright light during the day or the darkness of night, this structure picks up on this information and tells your cells to act accordingly. That said, your circadian rhythm is closely connected to day and night.

How Does It Affect Sleep?

Light exposure during the day causes the body’s internal clock to send signals that promote alertness. This helps keep you awake and active. As darkness sets in, the master clock instructs body cells to slow down. It also initiates the release of melatonin, a sleep hormone, to allow sleep to occur by making you feel tired and sleepy throughout the night.

This hormone peaks at around 2 – 4 A.M. before reducing in the morning, allowing wakefulness. In this way, the circadian rhythm synchronizes your wakefulness and sleep with day and night, thus creating a stable restorative sleep cycle that promotes increased daytime activity.

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What Else Does the Circadian Rhythms Affect Besides Sleep?

Aside from the sleep-wake cycle, the body clock controls virtually all body systems. For instance, your endocrine system controls hormones to match your daytime energy expenditure, and your digestive system secretes proteins to ensure you eat on schedule. Some researchers have linked circadian rhythms to weight and metabolism by regulating cholesterol and blood sugar.

They also influence mental health, including regulating the risk of psychiatric health concerns, such as depression and bipolar disorder, not to mention, the chances of getting neurodegenerative illnesses like dementia.

What’s more, there are indications that these rhythms have a crucial impact on the immune system and various processes of DNA repair that play a role in cancer prevention. Research has it that circadian cycles can impact the effectiveness of the anti-cancer medication.

How Do Circadian Rhythms Get Out of Sync?

While the circadian rhythm occurs naturally, various factors may affect it during the day. A disrupted rhythm can occur due to either an internal malfunction or a misalignment between the master clock and external forces, such as the social and work environment (for instance, if you stay up till late reading or have to work at night). Most combination sleepers also have a hard time sleeping due to the body movements of their partners at night. This can affect you if you don't have a quality mattress that can help minimize motion transfer. These disruptions can happen over the long term or short term.

They include:


Irregularly-timed light can significantly interfere with the normal functioning of the circadian rhythm. The CDC (Centers for Disease Control and Prevention) states that the circadian clock is very sensitive, especially about 2 hours before your usual bedtime. So, if you use bright light during this time, you may end up shifting the need to sleep later. This means that you may get tired and fall asleep later at night and wake up much later in the evening.

Poor Sleep Habits

Maintaining an unhealthy sleeping habit may disrupt your circadian rhythm across the day. Some activities that may throw your circadian clock out of sync include:

  • Using electronic devices late at night
  • Consuming caffeine late at night
  • Exercising late in the day
  • Eating and drinking late in the night
  • Having no set sleep time

Underlying Conditions (Circadian Rhythm Sleep Disorder)

Sleep experts have identified several types of circadian rhythm sleep disorders depending on their traits and causes.

Jet Lag Disorder

This is the most common circadian sleep problem. It occurs when a person travels across multiple time zones within a short period. Symptoms related to this condition include the following:

  • Poor concentration
  • Indigestion
  • Insomnia
  • Daytime sleepiness
  • Irritability

Until your circadian rhythm acclimates to the day-night cycle of your new location, you’re likely to have sleep-related issues and fatigue from jet lag. Some people may need about a week to adjust, while others may adapt to new time cues more quickly.

Shift Work Disorder

Shift work disorder mainly affects people who work rotating shifts or through the night and sleep during the day. Such people often find it challenging to get enough sleep. Their sleep is often fragmented as the brain is active and naturally programmed to be awake during the day. If your job requires you to work while others are sleeping, it will put your sleeping schedule at odds with the local daytime hours and keep you from setting a sleep pattern.

Delayed Sleep Phase Disorder (DSP)

This circadian rhythm disruption is mainly associated with teenagers and young adults who stay up late at night (night owls) and wake up late in the morning. While the exact cause is unknown, it may be related to underlying physical conditions, genetics, and your behavior.

Advanced Sleep Phase Disorder (ASP)

Unlike delayed sleep phase disorder, patients with ASP find that they get sleepy early in the evening and tend to wake up much early than usual. This disorder is relatively rare as it affects about 1% of individuals in the mid to older age range. It’s more common in older individuals.

This condition usually doesn’t interfere with regular working hours. Patients are more tolerant of it than of DSP. However, advanced sleep phase disorder does become an issue when sleepiness starts messing with your evening plans. You may have a hard time keeping business and social commitments.

Non-24 Hour Sleep-Wake Disorder

This sleep disorder occurs mainly in individuals who are blind and unable to receive the much-needed light-based cues for their circadian clock. While their body system still follows the standard 24-hour cycle, their sleep hours shift backward constantly by minutes or hours each time.

Irregular Sleep-Wake Rhythm Disorder

Patients with irregular sleep-wake rhythm disorder cannot set a specific sleep pattern irrespective of how hard they try. Instead, they may have many short sleeping periods or naps in 24 hours. This condition is mainly connected to disorders that affect the brain, like dementia.

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What Happens When Your Circadian Rhythm Is Off?

Maintaining your circadian rhythm is crucial to your health. If you have a disrupted circadian rhythm, you’ll experience both short and long-term consequences to your overall health.

For starters, it can lead to severe sleeping problems. With a misaligned body clock, you can have difficulty falling asleep, wake up during the night and even be unable to stay in bed as long as you want into the morning. Additionally, circadian rhythm disruptions contribute to various sleep disorders, such as obstructive sleep apnea (OSA).

Overall, a disrupted sleep-wake circadian rhythm means shallow, fragmented, and lower-quality sleep. It can also increase your risk of excessive daytime sleepiness and insomnia.

How to Maintain Healthy Circadian Rhythms

Resetting your circadian rhythms basically means resetting your sleeping and waking time. If possible, sleep and wake up at about the same time every day. If you’re having a hard time following a consistent sleep schedule, you can use your alarm clock to wake you up at the same time every day. This will help your body adjust to suitable sleep patterns and enco0urage tiredness when you need to fall asleep early and wake up early.

As light can disrupt circadian rhythms, it’s vital to decide when to limit light exposure. Generally, the 2 hours before bedtime are the most crucial. So, refrain from using blue light during this period to ensure a regular circadian rhythm.

Other healthy tips for sleeping better include:

  • Get daily exercise
  • Avoid caffeine
  • Keep naps short and early or avoid them completely
  • Limit light before bed
  • Avoid eating heavy meals late at night

Some calming supplements can also help people with trouble falling asleep sleep faster. However, it’s wise talking to your physician before using products with active ingredients.

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When to Talk to Your Doctor

Although it’s pretty normal to feel groggy sometimes, you may want to talk to your doctor if you experience sleep disruptions for a prolonged period. Consider making a doctor’s appointment if you:

  • Have trouble waking up
  • Find it hard to achieve adequate sleep every night
  • Feel extremely tired in the morning
  • Cannot fall asleep easily

For individuals with irregular sleep schedules, especially those who travel frequently or night shift workers, it may help to ask a sleep specialist about ways to reduce circadian disruptions.

Closing Thoughts

It’s worth noting that your biological rhythms are your body’s natural way of sticking to its 24-hour body clock, thus helping your body systems function on a healthy sleep-wake schedule. You’ll benefit the most from your day-to-day activities when your circadian rhythms are in sync. If you’re experiencing sleep problems and uncertain about your symptoms, you should speak with a healthcare provider for a complete diagnosis and a viable treatment plan. 

Ever had to reset your master clock before? What tips worked for you best? We’d like to hear your thoughts in the comments section below!

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