How Many Circadian Rhythms Do We Have (Yes, More Than One)

How Many Circadian Rhythms Do We Have (Yes, More Than One)

How Many Circadian Rhythms Do We Have (Yes, More Than One)

You feel best when your circadian rhythms are aligned amongst each other and with your external day. And the first step to getting there is to know how many circadian rhythms you have. And also, which are the most important ones for you. This is what we will have a look at in this post.

How many circadian rhythms do we have? You have one central circadian rhythm that especially controls your sleep-wake behavior and is influenced by light. In addition, your organs (influenced by eating timings) and your muscles (indirectly influenced through exercise) each have their circadian rhythm. And, finally, virtually every cell in your body has its own circadian rhythm.

Read on to get a full understanding of:

  • What the main circadian rhythms of your body are 
  • Why every cell in your body has its own circadian rhythm
  • What other circa-rhythms exist
  • My personal experiences and your key takeaways

Let’s get directly into it with a little overview of your circadian rhythms.

Our Circadian Rhythms

How Many Circadian Rhythms Are There

First off, your circadian rhythm is the natural, internal rhythm your body goes through every single day. It controls and optimizes all your functions and allocates a specific time frame to each. This is important because your body cannot do everything at the same time.

Read this post about “What Is the Circadian Rhythm and Why Do We Have One” to get the full story.

And now back to the original question about how many circadian rhythms there are. The short answer is many, but some are more important than others. Let me explain.

Each of the circadian rhythms in your body follows their respective internal clocks. This is a crucial part, so let me rephrase it again. Without an internal clock to follow, your body wouldn’t be able to produce a circadian rhythm. So, for your body to develop a circadian rhythm, it needs to follow an internal clock. And this is also the starting point for us.

Your body has many internal clocks that produce many circadian rhythms for you:

  1. The most important one is your central circadian rhythm that follows your central internal clock, called SCN. This controls your sleep-wake-behavior, your hormones, as well as your body functions and is largely triggered by your light exposure.
  2. Then comes the circadian rhythm in your organs that is controlled by your food timings. 
  3. Your muscles have a circadian rhythm that can be influenced by exercise and movement. 
  4. Finally, each of your cells has its own circadian rhythm.

Let us have a look at each of them in more detail now.

The Central One

Your Central (Master) Circadian Rhythm

First and most important, you have one central circadian rhythm. This is controlled by a small part in your brain that is your central internal clock (called the SCN). And this internal clock centrally sets your circadian rhythm when it shares your internal time with the rest of your body.1–3

What does this mean for you? Your body has optimized the timing of the functions that it goes through every day. Depending on the time your body thinks it is, the expression of these functions changes. Let’s have a look at a concrete example. Let’s have a look at hormones and sleep.

The most obvious expression of your circadian rhythm is your sleep-wake cycle (also called your chronotype). When you want to go to sleep and wake up again is strongly influenced by two hormones, melatonin, and cortisol. Melatonin helps you wind down and prepare your body for sleep at night. And cortisol helps you get energized and prepare your body to start the day.

Read all you need to know about your central circadian rhythm in this post about “What Are Chronotypes and How to Find out Yours.”

Your internal clock in your brain is indirectly connected to many areas that control hormone levels. Just like the pineal gland that produces the hormone melatonin. Or your adrenal gland that produces the hormone cortisol.

In this way, your circadian rhythm (through the internal time it gets from your internal clock) can increase your melatonin production in the evening to prepare your body for sleep at night. And then stop this production again in the morning to help you not be sleepy anymore. In the same way, your circadian rhythm can increase your cortisol production in the morning to help you feel energized and start your day. And stop this production again in the evening to not interfere with your sleep.

In the same way that hormones, like melatonin and cortisol, have a daily rhythm, also other body functions have one. For example, your heart rate, your blood pressure, and your body temperature have daily rhythms. These are at a low in the evening to help you sleep and rise again in the morning to prepare you to wake up.

And in the late afternoon/ early evening, your body temperature and muscle tone peak and your coordinative functions increase. This makes you less prone to injuries and to perceive your exercise intensity to be at a lower level. And this is also the time when your physical performance is at its peak.4,5

Also, your cognitive abilities follow your circadian rhythm. In the morning you are better at solving analytical problems and thinking strategically. In the afternoon, however, you are better at solving insight problems and thinking creatively.6

Ok, let’s take one step back again from what your central circadian rhythm influences. And let’s very briefly have a look at how it works.

Your central circadian rhythm is controlled by your central internal clock. This central internal clock is a small part of your brain that is located behind the bridge of your nose and called the SCN. And your SCN uses light information from your outside world to adjust your internal time.

Read all you need to know about your central circadian rhythm in this post about “How Does Your Circadian Rhythm Work.”

The One of Your Organs

The Circadian Rhythm of Your Organs

Just like light impacts your central circadian rhythm in your brain, food impacts the circadian rhythm in your organs. To be more specific, any calories that you consume impact the clocks in your organs. And the clocks in your organs set the circadian rhythm for your organs.

Simplified, your organs have two states that they can be in. Either a state where they have to digest calories. Or a state where they can repair and rejuvenate themselves. During the day, your organs are at their best to digest and process food. But at night they are not. They need that time to repair and rejuvenate themselves. This is their daily rhythm.3

In this sense, there is a time window when it is ideal for you to eat. And there is a time window when it is ideal for you not to eat. So that your organs can follow their ideal circadian rhythm of digesting during the day and repairing and rejuvenating at night.

But calories are precious for your body. Now, any calories you consume, even those from a small snack or caloric drink, you turn on your entire digestive system. The calories that you consume must be digested, absorbed, sorted, and metabolized and the waste must be cleared by your organs.

And when you consume any calories outside your ideal eating window, all your digestive organs have to participate in your digestive process. That also means that they have to stop repairing and rejuvenating themselves if that was what they were doing.

Unfortunately, it is easy to live against the circadian rhythm of your organs through the wrong food timings. Or against your central circadian rhythm through the wrong light exposures. Fortunately, there are a few simple things that will help you to align with your circadian rhythms. Read all you need to know about them in this post: “How to Get Your Circadian Rhythm Back on Track

The One of Your Muscles

The Circadian Rhythm of Your Muscles

The two most important circadian rhythms for you are your central circadian rhythm in your brain (controlled by light) and the circadian rhythm of your organs (controlled by food). But also your muscles have their circadian rhythm. And you can indirectly influence it through exercise.

Exercise in the morning will set you up for a great start to the day. And exercise in the afternoon is great for performance because at that time you are at your daily peak performance level. Let’s have a closer look.4,7

When you exercise then you increase an enzyme that is involved in the production of a pigment that is important for your muscle clock. And, hence, the circadian rhythm of your muscles. You exercise. Your body then increases the level of an enzyme. That enzyme is involved in the production of a pigment. And that pigment is an important part of your circadian rhythm.8

This pigment is called heme. It is in your blood and carries oxygen to all your tissues. And it also tells your internal clock to turn on or off specific genes that are involved in your metabolism. More specifically, your glucose and fat metabolism which your muscles both need to fuel your exercise, along with oxygen.

Long story short, also your muscles have a circadian rhythm. And you can indirectly influence it through exercise.

The One of Your Cells

The Circadian Rhythm of Your Cells

In short, there is also a circadian rhythm built into virtually every cell in your body. To appreciate this, let’s first take a step back and have a quick look at your genome: Your genome is the sum of all your genes. And every cell in your body has your full genome. 

Now, what these cells do depends on the specific genes of your genome that are turned on. These genes can encode everything in your body. And, naturally, the ones that are activated differ based on their location. For example, in your heart, there are different genes from your genome turned on than in your liver. Or your brain. Or any other part of your body.

And when these genes are turned on depends on their specific circadian rhythm. You can’t have all your genes turned on or off at the same time. That is why up to twenty percent of your genes can be turned on or off at different times of the day.9

The discovery of how this works and how your genes establish their circadian rhythm was awarded the Nobel Prize in Physiology or Medicine in 2017.10 Simplified, inside every cell, you have a period gene (or PER gene), that builds up a PER protein. And you have a timeless gene (TIM gene) that builds up a TIM protein. Once those two proteins are built in your cell, they are able to enter their cell nucleus, block their gene activity, and then break down again. This feedback loop slowly builds up and then breaks down every twenty-four hours.11

In short, these genes act like a circadian clock that can produce a circadian rhythm at the cellular level. And research suggests that this happens in every cell of your body.

Clock researchers have known for decades that single cells can produce daily rhythms because they could observe them in single-cell organisms. Just like those beautiful bioluminescent single-cells, which you can find across the beaches in places like Vieques in Puerto Rico.12

Other Rhythms

How Many Other Environmental Rhythms Are There

Our circadian rhythm follows our daily environment of day and night because it follows a cyclical and predictable pattern. And there has been evolutionary pressure to adapt to this pattern. But there are also other environments that follow cyclical and predictable patterns. And there has also been evolutionary pressure for organisms to adapt to these.

In total, there are four predictable and cyclical environments in nature:

  • The tidal cycle of 12.5 hours
  • The daily cycle of 24 hours
  • The lunar cycle of 29.5 days
  • The annual cycle of 365.25 days

And we can find organisms that have adapted to each of these four environments. These rhythms are self-sustained (meaning that they continue also without external information) and may deviate a little from the original in cycle length. That is why they are also called circa-rhythms. Just like our circadian rhythm.

So let’s have a brief look at each of these four environmental circa-rhythms.

Circadian Rhythm

The Circadian Rhythm

Circadian rhythms are present in virtually every organism: from us humans to other mammals and animals, to plants, and right down to those organisms that exist only as one single cell. The exception is those organisms that live in places the sun doesn’t reach, like in the deep sea or in caves.13

Circa-Annual Rhythm

The Circa-Annual Rhythm

Over the year, our seasons change. And with this also comes a change in daylight and ambient temperatures. A predictable and cyclical change. And this has been of strong enough evolutionary pressure for some organisms.

What is the first example of a circa-annual rhythm that comes to your mind? Maybe it is that of birds migrating. Or that of annual breeding seasons that many animals have. 

But did you know that we also used to have a strong circa-annual rhythm? No? Ok, so let’s have a look at us as an example.

We also used to have a significant circa-annual rhythm. Both daylight and ambient temperatures signaled our bodies what time of year it was. And we had, for example, annual reproductive peaks. But with the beginning of industrialization, we moved from working outside to inside. And when we are inside, we protect ourselves from seasonal fluctuations in both daylight and ambient temperatures. Since then, our circa-annual rhythm has become weaker than ever.14

Circa-Tidal Rhythm

The Circa-Tidal Rhythm

Tides are important for organisms that live in tidal zones. And also for those that feed on tidal organisms. So, when we are talking about circa-tidal rhythms, we are talking about marine life here that is affected by changes in their water environment, like water levels or pressure and also temperature. And about their predators.

One example of an organism with a circa-tidal rhythm is a marine algae called Hantzschia. When the tides are high, it descends into the sand. But when the tides are low, it rises back to the surface.15

Circa-Lunar Rhythm

The Circa-Lunar Rhythm

Some organisms have a circa-lunar rhythm that follows the waxing and waning of the moon. Even though these are, in comparison to the other three environmental rhythms (day/ night, year, tides) relatively few.9

Most examples of circa-lunar rhythms can be found with marine organisms. One example is the change in the size of the (edible) gonads of a species of sea urchins, depending on the lunar cycle. Another example, connected to the previous one, is the reproductive cycle of some marine animals that feed on these sea urchins.16

Personal Experiences

My Personal Experiences

If you have ever suffered from jet lag, then you know what it feels when your internal time is out of sync with your external time. And your circadian rhythm – that is based on your internal time – is out of sync with your external day.

This is also what happens to me, especially when I fly east. But there’s more to it. Because it is not just the central circadian rhythm that is out of sync with the external day, but all circadian rhythms. Initially, they are all still based on the local time they were adapted to.

But for me, or also for you or everybody else, the different circadian rhythms don’t adapt at the same rate. The circadian rhythm of my organs, that is triggered by food, usually adapts much faster. While my central circadian rhythm, that is triggered by light, needs a little longer to adapt.

And this misalignment of these two circadian rhythms is one of the reasons why we feel so off until we have fully adapted to a new time zone.

One trick I’m doing is to increase my natural light exposure. Especially during the morning and first part of the day in general. This helps to align my main circadian rhythm much faster than it normally would. And my jet lag is both less intense and over much sooner.

Read all you need to know about how to align your circadian rhythms in this post: “Get Your Circadian Rhythm Back on Track: The Ultimate Guide

Key Takeaways

Key Takeaways

Finally, there are six key takeaways that I want to share with you:

  1. You have one central circadian rhythm that controls your sleep-wake-behavior, your hormones, as well as your body functions. This is steered by a small part in your brain, just behind your nose bridge, and largely influenced by your light exposure.
  2. Your organs have their own circadian rhythm that largely depends on your food timings. The first calories you consume shift your organs into their digestive mode. And only about three hours after you have consumed their last calories can your organs change to their repair and rejuvenate mode.
  3. Also, your muscles have their circadian rhythm. And you can indirectly influence this rhythm through the timing of when you exercise.
  4. Finally, virtually every cell in your body has its circadian rhythm. And the discovery of how this process works was awarded the Nobel Prize in Physiology or Medicine in 2017.
  5. Next to the circadian rhythm, there are three other environmental circa-rhythms. The circa-annual rhythm that also used to be significant for us. And the circa-tidal and circa-lunar rhythm that are especially relevant for marine organisms.
  6. When you experience jet lag, also your circadian rhythms are misaligned. You can overcome jet lag faster if you increase your natural light exposure especially in the morning and first part of the day. This will help align your central circadian rhythm to your external day.

And now back to you: Have you already discovered how those different circadian rhythms work within your body?

Stay fit,





PS: If you found this information useful, spread the word and help those who would benefit most from it 🙂

References

References

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Hi, I'm Dennis

The content of every post is based on peer-reviewed, published studies combined with my own experience of translating those theories into real-life practice.

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