What is a Circadian Rhythm?

Understand how your body clock functions and controls your sleep cycles.

By Jayna Nickert

Our ability to function in a happy, healthy manner each day has a lot to do with our body’s natural clock. This internal clock is responsible for triggering hunger and sleepiness. It’s also linked with overall short- and long-term health.

When the biological clock is disrupted, there’s a direct negative impact on body functions that disrupt sleeping and eating patterns. Not only will we feel tired and unfocused when our body clock is off, we will also have an increased risk for chronic health problems, bipolar disorder, depression, obesity, diabetes, and sleep disorders.

This natural clock is referred to as the circadian rhythm.

What is a Circadian Rhythm?

Everyone has a circadian rhythm. It regulates when the body wants to sleep and wake up over a 24-hour cycle.

Each person’s circadian rhythm varies, but people typically become the most tired between the hours of 1-3 PM (after lunchtime), and from 2-4 AM. A circadian rhythm will stay balanced so long as we go to bed in the evening and rise in the morning around the same time each day—getting 7-9 hours of sleep per night.

Circadian rhythms dictate our level of brain activity, hormone production, cell regeneration, and several other biological activities that occur on a 24-hour cycle. Most living beings have a circadian rhythm. They’re found in animals, plants, and even tiny microbes.

In each of these living organisms, there are biological clocks found in nearly every organ and tissue that keep them on a timing system. Similar genes responsible for making up the components of a biological clock have been found in humans, mice, fruit flies, fungi, and more.

How Do Circadian Rhythms Work?

Circadian rhythms are controlled by a part of the brain that responds to lightness and darkness. This is why most humans sleep during the night and are awake when the sun is shining throughout the day.

This part of the brain holds what is referred to as the master clock. The master clock consists of a pair of cell populations which are found in the hypothalamus of the brain.

This pair of cell clusters is called the suprachiasmatic nuclei (SCN). This is where the genes that control circadian rhythms are located. Circadian clock genes are also located in the liver, kidneys, pancreas, muscles, etc., however, it’s the SCN that instructs the rest of the body to stay on schedule and how to take cues from the environment.

When the sun goes down, the SCN triggers the body to begin releasing melatonin, which helps the body become tired in preparation for sleep. Sunlight, on the other hand, restricts the release of melatonin and prompts feeling awake and energized.

The SCN is triggered when light enters the eyes, and this information is transformed into neural signals that set the body’s internal temperature. It’s through these fluctuations in body temperature that the circadian rhythm is regulated.

Circadian rhythms can influence the time of the day a person is born, as well as when a person could die due to its influence over hormones and blood pressure. The hormones that trigger labor, for example, are released during the evening as part of a natural defense mechanism, as the mother and baby are less susceptible to predators at night.

Studies have shown that more births occur after the hours of midnight than during the afternoon. Mornings, on the other hand, are more likely to bring death due to blood pressure changes. Blood pressure is its lowest during sleep, around 3 AM, and it rises dramatically upon waking up.

This increases the risk for a heart attack or stroke to be highest between the hours of 8 AM and noon. Asthma is also more intense in the mornings as less cortisol is produced during the night, which has an anti-inflammatory effect.

How Do Circadian Rhythms Change and Become Disrupted?

Circadian rhythms can change overtime as you age. They also may be altered by common disruptions such as traveling, working the night shift, or adjusting to Daylight Saving Time.

Sleepy young woman trying kill alarm clock while bury face in pillow. Early wake up, not getting enough sleep, getting work concept. Female stretching hand to ringing alarm willing turn it off

Changes in Circadian Rhythm as You Age

A person’s circadian rhythm can change over time with age. For example, teenagers are more inclined to have more energy late into the evening and to sleep later in the day.

With age, however, it’s common for a person to become more energized in the early morning hours and tired earlier in the evening. This isn’t always the case, but it does tend to change in this direction for a large percentage of the population.

Irregular Sleeping Patterns

When sleeping patterns change, the circadian rhythm will be disrupted. There are various situations in which this is common to occur.

  • Traveling: Circadian rhythms can become disrupted from traveling into different time zones—causing jet lag
  • Working the Night Shift: When a person works a night shift he/she may find sleeping during the day to be difficult, and eating patterns may also change. Night shift workers are more susceptible to experiencing sleep disorders, mood disorders, weight gain, health issues, and chronic fatigue.
  • Daylight Saving Time: DST is an instance during which a person’s circadian rhythm may become disrupted. It can take a while for the body to adjust to getting up and going to bed an hour earlier or later in the day.
  • Adjusting to College: College students face disruptions to their circadian rhythms due to their strenuous schedules that oftentimes require studying late into the evening.
  • Social Jet Lag: Social jet lag is a common circadian rhythm disruption that occurs when a person decides to stay up later than is typical on the weekends, and/or changes the time that he/she wakes up, exercises, eats, etc.

Having a disrupted circadian rhythm can cause numerous difficulties in a person’s day-to-day life, but there are ways to help improve circadian rhythm functioning.

Tips For Improving Circadian Rhythm Functioning

To improve the functioning of your circadian rhythm and help it stay on a regular schedule, there are a few steps you can take.

1. Determine Your Chronotype

Since each person’s body operates to its own unique rhythm, it’s important to determine your own circadian rhythm before attempting to try to improve its functioning. This involves determining your chronotype.

Your chronotype can be determined by examining when you personally have the most energy throughout the day. For some, this is in the morning, while for others, this happens later in the day and into the evening.

Chronotypes are related to genetics. If you can align your sleep pattern to your own circadian rhythm, it will help increase the amount of deep and REM you’re able to have each night.

2. Develop a Consistent Daily Schedule

One of the best ways to keep a circadian rhythm functioning well is by going to bed and waking up at the same time each day.

In addition to establishing a consistent sleep cycle, it’s also important to eat and exercise at the same time each day. It’s best to do anaerobic exercises later in the day. Overall, exercise should happen on a consistent basis for greater circadian rhythm functioning.

When it comes to eating, it’s most beneficial to eat the most calories earlier in the day and to finish eating by 6-7 PM with a lighter calorie meal. This will give the body adequate time to wind down for a good night’s rest. For optimal results, it’s important to stay on schedule into the weekend.

3. Manage Light Exposure

Since exposure to light impacts the circadian rhythm it’s important to limit exposure to light in the evening and to expose oneself to light in the morning.

Blue light from television, computer, and phone screens interfere with the body’s release of melatonin, and therefore have a negative impact on the circadian rhythm. Blue light filtering glasses may be worn to help combat this.

In order to gain more energy in the morning, it’s important to expose the body to light in order to stop the release of melatonin. They can be done by taking a walk in the morning, opening a window, or using light lamp therapy.

4. Invest in a Quality Mattress

Since the circadian rhythm is such an important and delicate system, it’s essential not to let anything stand in the way of a potentially good night’s rest that could disrupt your internal clock. This includes blocking out all interfering noises, or creating noise (if that helps), and investing in a quality mattress and pillows.

Nothing can make getting adequate rest more difficult than a worn out, or uncomfortable mattress. Even if a mattress is new, it may not be ideal for you. This is why it’s important to take a mattress quiz to determine your ideal mattress type and to invest in a quality option that meets your unique sleep preferences.

Having the right mattress could potentially improve not only your health but your quality of living and life expectancy. If you’d like some support in getting a better night’s rest we can help find the right mattress for you. Feel free to have a look at our mattress guides to get started.


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