Ok, so you know that your circadian rhythm plays a key role in your life. But did you also know that it is vital for virtually every function of your body? Or at least for their timing. This is because your circadian rhythm optimizes the timing of all your body functions. And this impacts your daily life more than you might imagine.

What does your circadian rhythm control? Your circadian rhythm controls the timing of virtually everything in your body. From your sleep-wake cycle to your physical and cognitive performance, to your mood, your immune system, the state of your organs, and even the efficiency of drugs you take and how much jet lag you experience.

Read on to get a full understanding of:

• What your circadian rhythm controls on a high level
• How your circadian rhythm controls your sleep-wake cycle
• What daily variations to expect in physical and cognitive performance as well as in your mood and how to make use of them
• Why the rhythm of your organs can be divided into two distinct parts and how to make the best out of this
• Why your immune system depends on a strong circadian rhythm
• Why you should take the timing of drugs seriously
• Why it is your circadian rhythm that determines how much jet lag you experience
• What happens when you mess up your circadian rhythm (short-term and long-term)
• My personal experiences and your key takeaways

Ok, let’s start with a quick overview of your circadian rhythm and it’s individual parts. And then we’ll directly go into what this means for you in your daily life.

High-Level Overview

High-Level Overview

First off, we live in an environment with a predictable daily cycle that always goes from day to night and back and that is always twenty-four-hours long. This is called your external day. And it has been an evolutionary advantage to adapt to this external day.^​1​

Your body has an internal clock that follows your external day. And your body also optimizes the timing of all your body functions to your external day. This is called your circadian rhythm. And, from an evolutionary perspective, the advantage of having a circadian rhythm has been so great that virtually every living organism has one (minus those that live in the deep sea or in caves).^​2​

Now, you have one central circadian rhythm that controls and orchestrates virtually everything in your body. It is like the master of all your other circadian rhythms and it sits in your brain, just behind your nose bridge, in a part called the SCN.^​3​

I can recommend you two posts to get to know more about your central (master) circadian rhythm:

• “What Is the Circadian Rhythm and Why Do We Have One”
• “How Does Your Circadian Rhythm Work: All You Need to Know”

Virtually every cell in your body has a circadian rhythm (coordinated by your SCN). Now, every cell holds your full DNA. And all your genes (called genome) are encoded in your DNA. What your cells do depends on which genes are turned on or off. And it turns out that different genes – up to twenty percent to be precise –  are turned on and off at different times of the day. That’s what your circadian rhythm does.^​1​

And this discovery of how your genes establish their circadian rhythm was awarded the Nobel Prize in Physiology or Medicine in 2017.^​4​

All your hormones have their circadian rhythm. And the two most prominent ones are melatonin and cortisol. Melatonin is high in the evening and at night and is vital to help you get a good sleep. Cortisol peaks in the morning and helps your body wake up and feel energized during the day.^​5,6​ But more about that later when we have a look at your sleep-wake cycle.

Your core body temperature has a circadian rhythm. It is highest in the afternoon, an important factor to help you reach your peak physical performance. And it is lowest at night, to help you get your best sleep.^​7​

And also your organs have a circadian rhythm. One that is basically divided into two parts. One, your digestion aka calorie uptake phase and two, their repair and rejuvenation phase. The first calories of the day start your digestion phase. And only about two hours after you’ve consumed your last calories of the day can your organs shift into their repair and rejuvenation phase. Until you consume your next calories again.^​8​

You’ve just seen how your circadian rhythm controls your body on an individual level. But that’s just one part of the story.

It will be much more interesting for you to find out what that means for your daily life. When they all come together. So let’s have a look at that next.

Impact on Your Daily Life

What Are the Implications for Your Daily Life

What you feel in your daily life are not the individual parts of your circadian rhythm (unless something goes really wrong). But it is the combination of all of those.

Together, the timing of each of these individual parts of your circadian rhythm determines:

• Your sleep-wake-cycle
• Your physical performance
• Your cognitive performance
• Your mood fluctuations
• The function of your organs
• The function of your immune system
• The efficacy of the drugs you take
• How much jet lag you experience

And that’s what we are having a look at now.

Sleep-Wake-Cycle

Your Sleep-Wake-Cycle (aka Your Chronotype)

Your circadian rhythm controls when you want to (or better are able to) fall asleep at night. And when you want to wake up again the next morning. And that sleep-wake-cycle is called your chronotype.

Read all about your chronotype in: “What Are Chronotypes and How to Find Out Yours”

And three the circadian rhythm of three parts are vital in this process:

1. Your core body temperature
2. Your “stress” hormone cortisol
3. Your “sleep” hormone melatonin

So, let’s see how they work together. In short, you get your best sleep, when your core body temperature is at its lowest point and your melatonin is at its high, while cortisol is at its low. Conversely, you feel refreshed and energized for the day when you wake up with high levels of cortisol and low levels of melatonin.

And you reach your physical peak when your core body temperature is at its peak. But more about that later.

Let’s have a look now at how that interplay between those parts of your circadian rhythm would look like in an ideal day:^​8​

• Before you wake up: Your body stops the production of your sleep hormone melatonin. And your core body temperature rises slightly. (Also your breathing and your heartbeat become slightly faster. And your blood pressure rises slightly.)
• When you wake up: When you are aligned with your circadian rhythm, then you wake up without an alarm clock. Your body stops producing melatonin. And starts ramping up the production of cortisol. You feel rested, full of energy, and ready to start the day.
• …
• During your evening: Your body stops producing cortisol and starts producing melatonin. This helps you to wind down and to prepare your body for sleep. Also, your core temperature starts to drop.
• When you go to bed: Your core temperature is at its lowest and your body ramps up the production of melatonin. And you are able to fall into a deep sleep without too much effort.

Now back to you. How closely does that reflect how you feel when you wake up or want to fall asleep?

Most likely, you have a weakened circadian rhythm. Your levels of melatonin and cortisol neither fully ramp up nor fully shut down. And your core body temperature is only at its lowest half-way through your night. Together, this means that you have issues both falling asleep and waking up energized and without an alarm clock.^​9,10​

The biggest reason for that? Your daily light exposure. In short, you don’t receive enough (natural) light during the day and too much (artificial) light at night. But there’s more to it. And you can read it all in this post: “Get Your Circadian Rhythm Back on Track: The Ultimate Guide”

Physical Performance

Your Physical Performance

Your circadian rhythm also controls your physical performance. At least indirectly through the peak timings of your body functions. And in general, two times are most beneficial for you to exercise. Either in the morning or in the late afternoon/ early evening.

Exercise in the morning has many benefits for you, thanks to your circadian rhythm. And one of these is that it helps you to build muscle mass and strength. Why? Because of the circadian rhythm of your testosterone levels. Those peak in the morning and are then about ten to twenty-five percent higher than during the afternoon and even higher than during the rest of the day.^​11​

Exercise in the late afternoon/ early evening to perform at your peak. Many body functions are at their peak during this time: Like your core body temperature (highly associated with exercise performance), your strength, your motor skills, or your reaction time.^​12​ 

Also, your lung function is at its peak and your circulatory system can distribute more oxygen and nutrients.^​13​ And your blood flow and blood pressure are advantageous for exercise in the afternoon.^​14​ This combination improves better oxygenation of your muscles.

When you put it all together, you will not only be able to perform at your peak in the late afternoon/ early evening (your performance can be as much as twenty-six percent higher) but you are also less prone to injuries than during any other time of the day.^​15​

Do you want to know all about the relationship between your circadian rhythm and exercise? Then I recommend you to check out this guide: “When Is the Best Time to Exercise Based On Your Circadian Rhythm”

Cognitive Performance

Your Cognitive Performance

Also, your cognitive performance follows your circadian rhythm. But its pattern is slightly different. In which way? It has one rather prolonged peak time. And a second one later.

You can think about it as your peak cognitive performance time during the first part of the day. A through in the early afternoon. And a rebound in your cognitive performance in the later afternoon.^​16​

What’s more? Depending on the time you are better doing one set of tasks than another:

1. In the first part of the day, you are best at doing analytical work
2. In the later afternoon, you are best at doing creative work

You are best at solving analytical problems in the first part of the day. Those are the problems that require your intense focus over a period of time. And you can usually solve them by solving their individual parts (aka narrowing down the problem space). One step at a time.

Now, here’s the thing. The later in the day you perform these tasks, the (relatively) worse your performance will be. Your mind simply becomes more fatigued. And that negatively affects your productivity.^​17,18​

Here’s what Harvard professor Francesca Gino has to say about that:^​19​

“Over the course of a regular day, everyone’s mental resources get taxed, research has consistently shown. Thus, as the day wears on, whether you like it or not, you become increasingly fatigued and consequently more likely to underperform on work tasks.”

Francesca Gino

But there’s also hope for you. And that comes in the form of taking a break. Because when you take a break, you significantly improve your performance afterward. And the more mentally fatigued and less able you are to solve such an analytical problem, the more a break will help you. Think of ten to twenty minutes of just shutting your brain off. Without any distractions (yes, also without any social media). And ideally in nature.^​17,20​

You are best at solving creative/ insight problems in the later afternoon. Those are the kind of problems where pure analytical capacity might hinder you to find a solution. Often, your knowledge and interpretation lead you down a dead-end that you need to break away from through insight. Like those “aha” moments you might remember.

In their paper aptly called “Time of day effects on problem solving: When the non-optimal is optimal,” Mareike Wieth and Rose Zacks show that you are better at solving those creative/ insight problems during your “non-optimal” times of the day. The reason is that you are less intensely focused and allow your mind to wander more. In this way, it can subconsciously explore different answers that you would otherwise consciously suppress.^​21​

“Innovation and creativity are greatest when we are not at our best, at least with respect to our circadian rhythms.”

Mareike Wieth and Rose Zacks

In short, your brain is normally at its peak in the first part of the day. Use this time to get your most important analytical work done. Don’t waste it with mundane tasks or on social media. Use your afternoons for more creative work. And if you still need to do analytical work later in the day, then make sure that you take regular breaks. Also, don’t make important decisions late in the day.

Mood Fluctuations

Your Mood Fluctuations

You can actually see a quite similar picture when you compare the circadian rhythm of your mood to that of your cognitive performance.

Your positive mood goes up in the morning. Then there’s a through (aka dip) in the early afternoon. And a rebound in the evening that this time leads to a peak in your positive mood.^​16​

First off, it is normal for you to feel good in the morning. Only to then feel slightly worse as the day goes on. With a low in the early afternoon.^​22​

This happens thanks to your circadian rhythm.^​23,24​

But then also know that your positive mood will recover later in the day. And you’ll reach your peak towards the evening.

Is there a quick way to boost your mood midday to overcome any dip? I’m glad you asked!

• Just like with your cognitive performance, a quick ten to twenty-minute break will help you boost your mood. Significantly more if you take this break in nature.^​20​
• Also brief meditation sessions – even when you have no prior meditation experience – have beneficial effects on your mood.^​25​

But what about if you have a (diagnosed) mood disorder? Well, also that can be connected to your circadian rhythm. But in a different way. As in that it happens when you disrupt your circadian rhythm.

Let me quote Colleen McClung, from the University of Pittsburgh, here, who wrote a paper called “How might circadian rhythms control mood? Let me count the ways…” where she stated the following:^​26​

“Nearly all people suffering from mood disorders have significant disruptions in circadian rhythms and the sleep/wake cycle. In fact, altered sleep patterns are one of the major diagnostic criteria for these disorders.”

Colleen McClung

Mood fluctuations are a normal part of your circadian rhythm. And you generally feel least positive during the early afternoon. But you now also know that you can combat that with a short break or brief meditation session.

Do you want to see the full picture of how your circadian rhythm controls your mood? Then I’d recommend you to check out the following post: “Your Circadian Rhythm Impacts Your Mood More Than You Think”

Organ Function

The Function of Your Organs

The circadian rhythm of your organs works slightly differently than the other ones we’ve seen so far. This is because instead of going through different levels of the same thing (like peak levels of a hormone), they basically switch between two states.

Here’s how those two states look like for your organs:^​8​

1. As soon as you start eating (read: consume any kind of calories), your organs start their digestive processes. And after you stop eating (yes, also any kind of small snacks or drinks with calories), they still need to work on your digestion for about two more hours.
2. Only about two hours after you stopped consuming any calories can your organs go into their repair and rejuvenate mode. And that is until you consume your next calories again.

Now, let’s have a look at a normal day for you. At what time do you normally start to consume your first calories? And at what time do you normally stop consuming any more calories? And remember that all calories count, no matter if they come from a little snack, the creamer in your coffee, or any caloric drink (like soda, wine, or beer).

If you are like most people, then you eat for too long and/ or too late, forcing your organs to work on your digestion and not giving them enough time to repair and rejuvenate themselves.^​27​

• You most likely believe that you consume your calories in a twelve-hour window (and do not count any drinks or late-night snacks).
• But you actually consume your calories for fifteen hours or more.
• And you consume your last calories too late, not allowing your organs to finish their digestive processes before you go to bed.

Ok, but what does that mean for your organs? You don’t allow your organs enough time to repair and rejuvenate themselves. And you force them to work at times when they should have stopped already. Making them less efficient in the process. You simply don’t allow them to follow their circadian rhythm.

Here’s what Satchin Panda, one of the leading chronobiologists of our time, has to say about this problem:^​8​

“Look at the total number of hours your stomach is at work. […] If this number is more than 12, here’s the good news: You have something to work on and it will have one of the biggest impacts on your health for the rest of your life.”

Satchin Panda

In short, you eat for too long and too late. And that disrupts the circadian rhythm of your organs. It doesn’t allow your circadian rhythm to control and optimize the timing of your organ functions. And it doesn’t allow your organs to repair and rejuvenate themselves enough.

Want to know how you can best change that? Check out this post: “When Is the Best Time to Eat – Based on Your Circadian Rhythm”

Immune System

The Function of Your Immune System

Your circadian rhythm also controls your immune system. And to better understand how, I’d like to show you that you don’t just have one immune system. Or, at least, that your immune system consists of two main parts.

1. The first line of protection: your rapid but nonspecific innate immune system
2. The second line of protection: your specific but non-rapid adaptive immune system

So, let’s have a very quick look at these two and see how they are controlled in different ways (or better, at different times) by your circadian rhythm.

The first line of protection: your rapid but nonspecific innate immune system. This is, from an evolutionary perspective, the ancient part of your immune system:^{​28–30​}

• Your first line of defense is physical barriers to overcome (like your skin, mucous, hair).
• Then, white blood cells recognize the pathogens (like bacteria, viruses, parasites, or cancer cells) and initiate a local inflammation to attract the right immune cells for an immediate response.
• Those immune cells then are like the first responders that get a general response against the respective type of pathogen.

Your rapid, nonspecific innate immune system is controlled by your circadian rhythm. And your innate immune system is at its peak during the day and late in the day. It is basically there for you at the time when you are most likely to need a rapid response from it.^{​29,31–33​}

Next, your rapid innate immune system alerts your specific adaptive immune system based on the respective kind of pathogen (bacteria, viruses, parasites, or cancer cells). And your adaptive immune system will further fight those pathogens until they are completely eliminated or inactivated.

The second line of protection: your specific but non-rapid adaptive immune system. This is, from an evolutionary perspective, the more recently developed part of your immune system:^{​28–30​}

• It consists of T and B lymphocyte cells (a type of white blood cell) that receive information about the kind of pathogen and its location from the innate immune system.
• These can respond specifically to the respective kind of pathogen and they can use their immunologic memory when they deal with a known pathogen.
• It is the coordinated response of both T and B cells that destroy the pathogen. And after they are successful, a subset of these become long-lived memory cells and, hence, part of your immunologic memory.

Also, your specific, adaptive immune system is controlled by your circadian rhythm. And your adaptive immune system generally is at its peak at night, before its numbers then decline in the morning and remain low during the day.^{​28,33–37​}

You can read all about the connection between your circadian rhythm and your immune system in this guide: “How to Use Your Circadian Rhythm to Boost Your Immune System”

Drug Efficacy

The Efficacy of the Drugs You Take

It has been long known that the timing of when you take a drug is important for how effective it is.^​38​ And that is because almost every drug target has a circadian rhythm.^​39​

Let me give you one example here: Just imagine that you had high cholesterol levels. And then you would know that the gene that makes a protein that then helps make cholesterol in your liver has a circadian rhythm. With the cholesterol production at its peak in the morning. Now, when would you want to take a drug that targets that specific gene? Yes, at the time when it’s most relevant.^​40​

Now, this was just one example. But it helps to illustrate the importance of taking your circadian rhythm into account when you take drugs. And to take the prescribed timing recommendations seriously.

Nearly all drug targets follow a circadian rhythm. And for some treatments, it has already been shown that the right timing can lead to improved drug efficiency with reduced side effects.^​39,41​

The drugs you take simply work best when you take them at the right time of day or night. And you can read more about it in this guide: “How to Use Your Circadian Rhythm to Boost Your Immune System”

Jet Lag

How Much Jet Lag You Experience

Your circadian rhythm also controls how much jet lag you experience. Or, better, how much jet lag you experience depends on how much out of sync your circadian rhythm is with your new local time.

You’ve seen all the examples that your circadian rhythm controls above. Now imagine that all of those would happen three hours later. Or four hours earlier. That would really mess up your day. Until you get them to happen at the right time again. But that is also what would happen if you travel three hours to the east or four hours to the west.

You experience jet lag because of two main problems with your circadian rhythm:^​42,43​

1. Your circadian rhythm is not aligned with your new local time.
2. The timings of your body functions are not aligned with each other anymore.

When you arrive at a new local time zone, you also need to let your circadian rhythm know. So that the timing of all your internal body functions matches the time of your external day.

Here’s what leading researchers Charmane Eastman and Helen Burgess say in their paper called “How To Travel the World Without Jet Lag”:^​42​

“The most effective treatments for jet lag rely on shifting the circadian clock to the new time zone as fast as possible.”

Charmane Eastman and Helen Burgess

And how do you shift your circadian clock to beat jet lag? In short, you need to use the right environmental cues at the right time. And those environmental cues are your daily light exposure, your eating timings, and when you exercise.

You can read all about it here in: “Use Your Circadian Rhythm to Beat Jet Lag: The Ultimate Guide”

Consequences of Disruption

What Happens When Your Circadian Rhythm Is Messed Up

When your circadian rhythm is disrupted, then the timing of all your body functions is disrupted too.

And there are two main ways to mess up your circadian rhythm:

1. You have a weakened circadian rhythm because your environmental cues (that your circadian rhythm needs) are not strong enough. As a result, the highs and lows of your body functions are dampened and their timings are off too.
2. You have a disrupted circadian rhythm because of the “wrong” timing of your environmental cues. This could be because of jet lag, shift work, or any similar lifestyle.

You can easily feel the difference in your life if it is something acute, like jet lag or shift work. But when the problem is your lifestyle, then you might have accepted a weakened or disrupted circadian rhythm already as your normal.

So, let me highlight what that means for your daily life through two examples:

1. Your sleep-wake cycle: what you feel in your everyday life
2. Your immune system: what the long-term consequences are

Sleep-Wake Cycle

How a Weakened or Disrupted Circadian Rhythm Messes Up Your Sleep-Wake Cycle in the Short-Term

You’ve seen above in the jet lag section that a disrupted circadian rhythm that is shifted by a few hours also shifts your sleep-wake cycle. And you have most likely already experienced this feeling if you were flying across time zones before. Or simply thanks to daylight savings time.

Now, let’s have a look at something more chronic. Something that you most likely experience without realizing it. Or with thinking that this is the normal state for you. Let’s have a look at what a weakened circadian rhythm does to your sleep-wake cycle.^​8,16​

	Strong circadian rhythm	Weak circadian rhythm
Before you wake up	Your body stops the production of your sleep hormone melatonin. And your core body temperature rises slightly.	Your body still continues the production of your sleep hormone melatonin. Your core body temperature doesn’t rise as much.
When you wake up	When you are aligned with your circadian rhythm, then you wake up without an alarm clock. Your body stops producing melatonin. And starts ramping up the production of cortisol.	You need an alarm clock to wake up. Your body still produces melatonin. And not enough cortisol yet.
Result	You feel rested, full of energy, and ready to start the day.	You wake up still tired and not full of energy.

One big differentiating factor you can see between a strong and a weak circadian rhythm is how you wake up. Naturally and fully refreshed. Or with an alarm clock and still tired.

But hey, you might blame that on not being able to fall asleep early enough. And if you have to get up too early then you might be right. And once in a while, you might just have to deal with it. But it’s a different story if this regularly happens. And for eighty-five percent of the population, waking up with an alarm clock is the norm.^​10​

Now, let’s have a look at what happens in your body during the evening if you have a strong vs weak circadian rhythm.^​8,16​

	Strong circadian rhythm	Weak circadian rhythm
During your evening	Your body stops producing cortisol and starts producing melatonin. This helps you to wind down and to prepare your body for sleep. Also, your core temperature starts to drop.	Your body still continues the production of your cortisol and doesn’t produce (enough) melatonin yet. Your core body temperature only drops later.
When you go to bed	Your core temperature is at its lowest and your body ramps up the production of melatonin.	Your core body temperature is still too high and only reaches its low point later at night. You still produce too much cortisol and not enough melatonin yet.
Result	You are able to fall into a deep sleep without too much effort.	You have a hard time falling asleep and also your sleep quality is suboptimal.

One reason for you to only be able to fall asleep at later times might just be your natural sleep-wake cycle, called the chronotype. Some people are later chronotypes than others.

Have a look at this post to find out all about it: “What Are Chronotypes and How to Find Out Yours”

However, the biggest contributing factor for this is are your environmental cues. First and foremost your daily light exposure.

If you feel like you have a weakened circadian rhythm just by comparing your mornings and evenings to the tables above, don’t worry. There are a few ways that you can include in your lifestyle to change that.

To strengthen your circadian rhythm, I can only highly recommend you to check out this post: “Get Your Circadian Rhythm Back on Track: The Ultimate Guide”

But wait, there’s also another phenomenon that happens with a great many people: Their sleep-wake cycle differs quite a bit between weekdays and the weekend. If you fall into this category, then you experience something called social jet lag.

Read all about it here in this post: “What Is Social Jet Lag and How to Overcome It”

Ok, so much about your daily life. Or at least about how you mess up your sleep-wake cycle when you weaken your circadian rhythm.

But what are the long-term consequences of having a weak circadian rhythm?

Health & Well-Being

How a Weakened or Disrupted Circadian Rhythm Messes Up Your Health and Well-Being in the Long-Term

Ok, let’s take a look at the bigger picture now. Let’s take a look at what happens over time if you live with a weakened or disrupted circadian rhythm.

1. This is what happens if you disrupt your circadian rhythm for one or a few days: Your brain cannot ensure that your body is doing the right things at the right time. Neither your body nor your mind will function optimally. You have reduced energy levels during the day and a reduced sleep quality at night.^​8​
2. This is what happens if you disrupt your circadian rhythm for weeks or months: What comes next? Your immune system. It cannot work anymore as it should.^​28,29​ This makes you more prone to infections and communicable diseases.^​44​
3. This is what happens if you live your life against your circadian rhythm: You are now also more prone to non-communicable diseases. Those that you develop because of your lifestyle. Also, those that are chronic and normally come to you to stay with you (including cancer^​45,46​, cardiovascular diseases^​47​, metabolic syndromes^​47,48​ like obesity, gastrointestinal diseases^​49​, diabetes^​50,51​, atherosclerosis^​41,52​). And also those that account for 71% of all deaths globally.^​53​

In their paper about the “Circadian Organization of the Immune Response” Daniel Cardinali and colleagues wrote the following:^​54​

“The circadian clock is one of the most indispensable biological functions”

Cardinali et al.

And I guess from the list above you can easily see why that would be the case. Now, with all these things in mind, what would be your next steps? I can strongly recommend you to (slightly) adapt your lifestyle to strengthen your circadian rhythm.

How could you do this? I’m glad you asked! Take a look at those three guides:

• “Get Your Circadian Rhythm Back on Track: The Ultimate Guide”
• “What Is Social Jet Lag and How to Overcome It”
• “How to Use Your Circadian Rhythm to Boost Your Immune System”

Personal Experiences

My Personal Experiences

There are a few things that I do to strengthen my circadian rhythm and to also make use of its daily variations. Here is what I actively try to do every single day:

• I try to get a high natural light exposure during the day and limit any artificial light exposure in the evening and at night to strengthen my circadian rhythm and help with my sleep-wake cycle. And the difference this makes doesn’t cease to amaze me.
• I always try to do my most intense workouts in the late afternoon/ early evening to maximize my performance and minimize my injury risk.
• I get my most important work done in the first part of the day and schedule the more creative parts for later times.
• I know that there might be mood fluctuations during the day and use breaks and meditation sessions to overcome these already before they appear.
• I help my organs to function better by allowing them plenty of time to repair and rejuvenate themselves. I only eat for a few hours every day during lunchtime.

Key Takeaways

Key Takeaways

Finally, there are two key takeaways that I want to share with you about how your circadian rhythm controls your life:

1. Your body is controlled by your circadian rhythm. You have a central circadian rhythm that sits in your brain and is in control to orchestrate the rest of your body. And virtually every cell, your hormones, your core temperature, and your organs have circadian rhythms. And all of these together impact your daily life and beyond.
   • Sleep-wake cycle: Your circadian rhythm controls when you want to (or better are able to) fall asleep at night. And when you want to wake up again the next morning. And also how good your sleep quality is and how refreshed and energized you are.
   • Physical performance: Your circadian rhythm controls those factors that are important e.g., to exercise at your peak performance with lowest injury risk (in the afternoon) or to build strength (in the morning).
   • Cognitive performance: In the first part of the day is when you are at your peak cognitive performance and you are best at doing analytical work. Then you go through a low. And in the later afternoon, you are best at doing creative work.
   • Mood fluctuations: Your positive mood is highest in the morning, then slowly goes down, before it peaks in the evening.
   • Organ functions: Your organs can be in two distinctive states, either in their digestive state during the times you eat (from the first calories in the morning to about two hours after your last ones of the day) or in their repair and rejuvenate state when they are done with your digestive process. Ensure enough time for the latter.
   • Immune system: Your circadian rhythm controls the interplay of the two arms of your immune system. The rapid innate immune system is most active during the day. And the specific adaptive immune system is most active during the night.
   • Drug efficacy: Almost every drug target in your body has a circadian rhythm. And the right timing when you take them can lead to improved drug efficiency with reduced side effects.
   • Jet lag: How much jet lag you experience depends on how much out of sync your circadian rhythm is with your new local time.
2. When you weaken or disrupt your circadian rhythm, then the timing of all your body functions is messed up too.
   1. In the short-term: Your brain cannot ensure that your body is doing the right things at the right time. Neither your body nor your mind will function optimally. You have reduced energy levels during the day and a reduced sleep quality at night.
   2. In the long-term: Now, also your immune system cannot work anymore as it should. First, This makes you more prone to infections and communicable diseases. Then, you will also become more prone to non-communicable diseases.

And now back to you: If you reflect on your daily life, have you already noticed the impact your circadian rhythm has on your life? And did you gain any insights on what you might want to prevent or overcome?

Stay fit,

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

References

References

1. 1.

   Roenneberg T. Internal Time. Harvard University Press; 2012.
2. 2.

   Takahashi JS. Circadian-clock regulation of gene expression. Current Opinion in Genetics & Development. Published online January 1993:301-309. doi:10.1016/0959-437x(93)90038-q
3. 3.

   Weaver DR. The Suprachiasmatic Nucleus: A 25-Year Retrospective. J Biol Rhythms. Published online April 1998:100-112. doi:10.1177/074873098128999952
4. 4.

   NobelPrize.org -. The Nobel Prize in Physiology or Medicine 2017. The Nobel Prize in Physiology or Medicine 2017. Published 2017. https://www.nobelprize.org/prizes/medicine/2017/summary/
5. 5.

   Rohatagi S, Bye A, Mackie AE, Derendorf H. Mathematical modeling of cortisol circadian rhythm and cortisol suppression. European Journal of Pharmaceutical Sciences. Published online November 1996:341-350. doi:10.1016/s0928-0987(96)00174-1
6. 6.

   Kennaway D, Wright H. Melatonin and Circadian Rhythms. CTMC. Published online February 1, 2002:199-209. doi:10.2174/1568026023394380
7. 7.

   Waterhouse J, Drust B, Weinert D, et al. The Circadian Rhythm of Core Temperature: Origin and some Implications for Exercise Performance. Chronobiology International. Published online January 2005:207-225. doi:10.1081/cbi-200053477
8. 8.

   Panda S. The Circadian Code. Rodale Books; 2018.
9. 9.

   Richardson G. The human circadian system in normal and disordered sleep. J Clin Psychiatry. 2005;66 Suppl 9:3-9; quiz 42-43. https://www.ncbi.nlm.nih.gov/pubmed/16336035
10. 10.

    Pilz LK, Keller LK, Lenssen D, Roenneberg T. Time to rethink sleep quality: PSQI scores reflect sleep quality on workdays. Sleep. Published online February 6, 2018. doi:10.1093/sleep/zsy029
11. 11.

    Brambilla DJ, Matsumoto AM, Araujo AB, McKinlay JB. The Effect of Diurnal Variation on Clinical Measurement of Serum Testosterone and Other Sex Hormone Levels in Men. The Journal of Clinical Endocrinology & Metabolism. Published online March 1, 2009:907-913. doi:10.1210/jc.2008-1902
12. 12.

    Teo W, Newton M, McGuigan M. Circadian rhythms in exercise performance: implications for hormonal and muscular adaptation. J Sports Sci Med. 2011;10(4):600-606. https://www.ncbi.nlm.nih.gov/pubmed/24149547
13. 13.

    Medarov B, Pavlov V, Rossoff L. Diurnal variations in human pulmonary function. Int J Clin Exp Med. 2008;1(3):267-273. https://www.ncbi.nlm.nih.gov/pubmed/19079662
14. 14.

    Thun E, Bjorvatn B, Flo E, Harris A, Pallesen S. Sleep, circadian rhythms, and athletic performance. Sleep Medicine Reviews. Published online October 2015:1-9. doi:10.1016/j.smrv.2014.11.003
15. 15.

    Facer-Childs E, Brandstaetter R. The Impact of Circadian Phenotype and Time since Awakening on Diurnal Performance in Athletes. Current Biology. Published online February 2015:518-522. doi:10.1016/j.cub.2014.12.036
16. 16.

    Pink DH. When: The Scientific Secrets of Perfect Timing. Text Publishing; 2018.
17. 17.

    Sievertsen HH, Gino F, Piovesan M. Cognitive fatigue influences students’ performance on standardized tests. Proc Natl Acad Sci USA. Published online February 16, 2016:2621-2624. doi:10.1073/pnas.1516947113
18. 18.

    Pope NG. How the Time of Day Affects Productivity: Evidence from School Schedules. Review of Economics and Statistics. Published online March 2016:1-11. doi:10.1162/rest_a_00525
19. 19.

    Gino F. Don’t Make Important Decisions Late in the Day: Cognitive fatigue affects your judgment and performance. Harvard Business Review. Published online 2016.
20. 20.

    Finkbeiner KM, Russell PN, Helton WS. Rest improves performance, nature improves happiness: Assessment of break periods on the abbreviated vigilance task. Consciousness and Cognition. Published online May 2016:277-285. doi:10.1016/j.concog.2016.04.005
21. 21.

    Wieth MB, Zacks RT. Time of day effects on problem solving: When the non-optimal is optimal. Thinking & Reasoning. Published online November 2011:387-401. doi:10.1080/13546783.2011.625663
22. 22.

    Golder SA, Macy MW. Diurnal and Seasonal Mood Vary with Work, Sleep, and Daylength Across Diverse Cultures. Science. Published online September 29, 2011:1878-1881. doi:10.1126/science.1202775
23. 23.

    Murray G, Allen NB, Trinder J. MOOD AND THE CIRCADIAN SYSTEM: INVESTIGATION OF A CIRCADIAN COMPONENT IN POSITIVE AFFECT. Chronobiology International. Published online January 2002:1151-1169. doi:10.1081/cbi-120015956
24. 24.

    Murray G, Nicholas CL, Kleiman J, et al. Nature’s clocks and human mood: The circadian system modulates reward motivation. Emotion. Published online 2009:705-716. doi:10.1037/a0017080
25. 25.

    Zeidan F, Johnson SK, Gordon NS, Goolkasian P. Effects of Brief and Sham Mindfulness Meditation on Mood and Cardiovascular Variables. The Journal of Alternative and Complementary Medicine. Published online August 2010:867-873. doi:10.1089/acm.2009.0321
26. 26.

    McClung CA. How Might Circadian Rhythms Control Mood? Let Me Count the Ways… Biological Psychiatry. Published online August 2013:242-249. doi:10.1016/j.biopsych.2013.02.019
27. 27.

    Gill S, Panda S. A Smartphone App Reveals Erratic Diurnal Eating Patterns in Humans that Can Be Modulated for Health Benefits. Cell Metabolism. Published online November 2015:789-798. doi:10.1016/j.cmet.2015.09.005
28. 28.

    Labrecque N, Cermakian N. Circadian Clocks in the Immune System. J Biol Rhythms. Published online April 20, 2015:277-290. doi:10.1177/0748730415577723
29. 29.

    Cermakian N, Lange T, Golombek D, et al. Crosstalk between the circadian clock circuitry and the immune system. Chronobiology International. Published online May 22, 2013:870-888. doi:10.3109/07420528.2013.782315
30. 30.

    Clark R, Kupper T. Old Meets New: The Interaction Between Innate and Adaptive Immunity. Journal of Investigative Dermatology. Published online October 2005:629-637. doi:10.1111/j.0022-202x.2005.23856.x
31. 31.

    Haus E, Smolensky MH. Biologic Rhythms in the Immune System. Chronobiology International. Published online January 1999:581-622. doi:10.3109/07420529908998730
32. 32.

    Mazzoccoli G, Vendemiale G, La Viola M, et al. Circadian Variations of Cortisol, Melatonin and Lymphocyte Subpopulations in Geriatric Age. Int J Immunopathol Pharmacol. Published online January 2010:289-296. doi:10.1177/039463201002300127
33. 33.

    Born J, Lange T, Hansen K, Mölle M, Fehm H. Effects of sleep and circadian rhythm on human circulating immune cells. J Immunol. 1997;158(9):4454-4464. https://www.ncbi.nlm.nih.gov/pubmed/9127011
34. 34.

    Dimitrov S, Benedict C, Heutling D, Westermann J, Born J, Lange T. Cortisol and epinephrine control opposing circadian rhythms in T cell subsets. Blood. Published online May 21, 2009:5134-5143. doi:10.1182/blood-2008-11-190769
35. 35.

    Besedovsky L, Born J, Lange T. Endogenous glucocorticoid receptor signaling drives rhythmic changes in human T‐cell subset numbers and the expression of the chemokine receptor CXCR4. FASEB j. Published online September 19, 2013:67-75. doi:10.1096/fj.13-237958
36. 36.

    Abo T, Kawate T, Itoh K, Kumagai K. Studies on the bioperiodicity of the immune response. I. Circadian rhythms of human T, B, and K cell traffic in the peripheral blood. J Immunol. 1981;126(4):1360-1363. https://www.ncbi.nlm.nih.gov/pubmed/6970770
37. 37.

    Kirsch S, Thijssen S, Alarcon Salvador S, et al. T-cell Numbers and Antigen-specific T-cell Function Follow Different Circadian Rhythms. J Clin Immunol. Published online July 15, 2012:1381-1389. doi:10.1007/s10875-012-9730-z
38. 38.

    Ede MCM. Circadian rhythms of drug effectiveness and toxicity. Clinical Pharmacology & Therapeutics. Published online November 1973:925-935. doi:10.1002/cpt1973146925
39. 39.

    Wei K, Wang Q, Gan J, et al. Mapping genes for drug chronotherapy. Drug Discovery Today. Published online November 2018:1883-1888. doi:10.1016/j.drudis.2018.06.011
40. 40.

    Merrow M, Roenneberg T. Circadian clocks: how rhythms structure life. Presented at the: coursera; 2019; Ludwig-Maximilians-Universität München (LMU).
41. 41.

    Winter C, Soehnlein O. The potential of chronopharmacology for treatment of atherosclerosis. Current Opinion in Lipidology. Published online October 2018:368-374. doi:10.1097/mol.0000000000000545
42. 42.

    Eastman CI, Burgess HJ. How to Travel the World Without Jet Lag. Sleep Medicine Clinics. Published online June 2009:241-255. doi:10.1016/j.jsmc.2009.02.006
43. 43.

    Waterhouse J, Reilly T, Atkinson G, Edwards B. Jet lag: trends and coping strategies. The Lancet. Published online March 2007:1117-1129. doi:10.1016/s0140-6736(07)60529-7
44. 44.

    Zhuang X, Rambhatla SB, Lai AG, McKeating JA. Interplay between circadian clock and viral infection. J Mol Med. Published online September 30, 2017:1283-1289. doi:10.1007/s00109-017-1592-7
45. 45.

    Straif K, Baan R, Grosse Y, et al. Carcinogenicity of shift-work, painting, and fire-fighting. The Lancet Oncology. Published online December 2007:1065-1066. doi:10.1016/s1470-2045(07)70373-x
46. 46.

    Savvidis C, Koutsilieris M. Circadian Rhythm Disruption in Cancer Biology. Mol Med. Published online July 17, 2012:1249-1260. doi:10.2119/molmed.2012.00077
47. 47.

    Scheer FAJL, Hilton MF, Mantzoros CS, Shea SA. Adverse metabolic and cardiovascular consequences of circadian misalignment. Proceedings of the National Academy of Sciences. Published online March 2, 2009:4453-4458. doi:10.1073/pnas.0808180106
48. 48.

    Roenneberg T, Allebrandt KV, Merrow M, Vetter C. Social Jetlag and Obesity. Current Biology. Published online May 2012:939-943. doi:10.1016/j.cub.2012.03.038
49. 49.

    Codoñer-Franch P, Gombert M. Circadian rhythms in the pathogenesis of gastrointestinal diseases. WJG. Published online October 14, 2018:4297-4303. doi:10.3748/wjg.v24.i38.4297
50. 50.

    Gale JE, Cox HI, Qian J, Block GD, Colwell CS, Matveyenko AV. Disruption of Circadian Rhythms Accelerates Development of Diabetes through Pancreatic Beta-Cell Loss and Dysfunction. J Biol Rhythms. Published online September 15, 2011:423-433. doi:10.1177/0748730411416341
51. 51.

    Marcheva B, Ramsey KM, Buhr ED, et al. Disruption of the clock components CLOCK and BMAL1 leads to hypoinsulinaemia and diabetes. Nature. Published online June 18, 2010:627-631. doi:10.1038/nature09253
52. 52.

    Haupt CM, Alte D, Dörr M, et al. The relation of exposure to shift work with atherosclerosis and myocardial infarction in a general population. Atherosclerosis. Published online November 2008:205-211. doi:10.1016/j.atherosclerosis.2007.12.059
53. 53.

    World Health Organization -. Noncommunicable diseases (NCDs), also known as chronic diseases, kill 40 million people each year. Non communicable diseases. Published 2018. https://www.who.int/news-room/fact-sheets/detail/noncommunicable-diseases
54. 54.

    Cardinali DP, Esquifino AI, Maestroni GJM, Pandi-Perumal SR. Circadian Organization of the Immune Response. In: Neuroimmunology of Sleep. Springer US; :59-84. doi:10.1007/978-0-387-69146-6_3