Environmental cues impact your circadian rhythm every single day. And that’s a good thing because your circadian rhythm uses these to align to your external day. Unfortunately, our modern environments have changed their influence in a way that they may weaken or even disrupt your circadian rhythm. But once you know what they are and how they impact you, you can use them to entrain your circadian rhythm. So let’s have a look at this now.

Which three environmental cues entrain your circadian rhythm? The entrainment of your circadian rhythm is the synchronization with your external day. The three most powerful environmental cues for this are your daily light exposure (by far the most powerful one), your eating timings, and your exercise & movement timings (a distant third).

Read on to get a full understanding of:

• What entrainment is and why environmental cues are important for your circadian rhythm
• What the three environmental cues are and how they impact by your daily life and our modern environments
• What other commonly believed environmental cues are that either used to impact your circadian rhythm, were thought to impact it (but actually don’t), or even disrupt it
• How to use the three environmental cues to your advantage
• My experiences and your key takeaways

Let’s start with a quick overview of entrainment. And then have a look at what the three most powerful environmental cues are and how they entrain your circadian rhythm.

The Top Three

Why Light, Food, and Exercise Are the Three Most Powerful Environmental Cues That Entrain Your Circadian Rhythm

Your circadian rhythm is like a schedule that your body follows every single day to optimize all its functions. This is important because:^​1​

• Your body can’t perform all its functions once.
• Some functions only make sense during specific times of the day.

And this daily schedule (your circadian rhythm) is based on your body’s internal time. 

There’s only one little problem: your internal time and consequently your circadian rhythm is not exactly twenty-four hours long. Circadian actually comes from the Latin “circa” (about) and “dies” (day). Franz Halberg coined this term in 1959 because your circadian rhythm – the daily rhythm of your body – is not exactly but only about-twenty-four-hours long.^​2​

Want to find out how long your circadian rhythm is? Check it out in here: “How Long Is Your Circadian Rhythm (Why Not 25h?)”

So, how does your body align your internal time to your external exactly-twenty-four-hours long day? It uses environmental cues. And this process is called entrainment.^​3​

If you want to find out all the details, you can find them in this post about “How Does Your Circadian Rhythm Work: All You Need to Know.”

With that in mind, let’s have a look at the three most important environmental cues that entrain your circadian rhythm now:

1. The by far most powerful environmental cue is your daily light exposure.
2. The second most powerful one is the timing of when you eat.
3. In a distant third place is the timing of your exercise & movement.

Btw, those environmental cues are referred to as zeitgebers. This is a German term that literally translates as “time-givers” and was coined by Jürgen Aschoff, one of the founders of the field of chronobiology.^​4​

Light

Why Light Is the By Far Most Powerful Environmental Cue to Entrain Your Circadian Rhythm

Light is the by far most powerful and important environmental cue for your circadian rhythm. In fact, light controls your central circadian rhythm, which then orchestrates all other circadian rhythms in your body.^​5,6​

Wait… what? Yes, there’s more than one circadian rhythm.

This is because many parts of your body have their own biological clock (even down to a cellular level). And those parts perform their functions based on both their daily schedule and the time on their biological clock. 

And the role of your master circadian rhythm is to align all of these. 

You can read all about your central and your other circadian rhythm in this post: “How Many Circadian Rhythms Do We Have”

Let’s have a quick look at how this works:^​7​

• You have a master circadian rhythm that is controlled by a tiny part of your brain called the SCN.
• And to get its time of day information, your SCN relies on special receptors in your eyes.
• These receptors are triggered by light – and are especially sensitive to blue-light-rays. 

Tadaa! That’s why light is the most powerful environmental cue for your circadian rhythm. Blue-light-rays to be more precise.

And whatever light information your SCN receives, it has three basic options to entrain your circadian rhythm to the external day:

1. It can speed up your circadian rhythm
2. It can leave your circadian rhythm as it is
3. It can slow down your circadian rhythm

So far so good. 

But your body adapted to natural sunlight as its environmental cue. This means that:

• Your body expects massive amounts of (natural) light during the day.
• And virtually no light in the evening and at night. Especially no artificial light that is high in blue-light-rays.

Want to get the full overview of how that works? You can read all about it in this post: “How Does Your Circadian Rhythm Work”

But here’s the thing: This is very different in our modern environments:

• You don’t receive enough light at times your SCN expects and needs it. This weakens your circadian rhythm. It is as if your SCN is not fully sure about the time of day and doesn’t fully upregulate or downregulate your body functions.
• You receive too much light when your SCN doesn’t expect any more light. This also weakens your circadian rhythm.

Check out tips #1 to #9 in this post about “How to Get Your Circadian Rhythm Back on Track” for practical information about how you can use light as an environmental cue (zeitgeber) to set yourself up for a strong circadian rhythm.

To sum it up, light is by far the most powerful environmental cue to entrain your master circadian rhythm. And your master circadian rhythm synchronizes all the other circadian rhythms through the time of day information you receive from light (especially blue-light-rays).

Food

Why Food Is the Second Most Powerful Environmental Cue to Entrain Your Circadian Rhythm

Just like light as an environmental cue impacts your master circadian rhythm, food as an environmental cue impacts the circadian rhythm of your organs. To be more specific, the timing of any calories consumed impact the circadian rhythm of your organs.^​8​

This also means that the circadian rhythm of your organs depends on at least two environmental cues. For one, it directly depends on your food timings. And then, it indirectly depends on your light exposure, which affects your master circadian rhythm, which then synchronizes all your circadian rhythms, including that of your organs. 

But why is food such a powerful (additional) zeitgeber for your organs? Simply because it was vital for our survival during our evolution. And having been able to extract virtually all available calories has been an evolutionary advantage during times of food shortages. It was vital for survival. That might be different today in times of abundance, but it’s still how your body works.^​9​

And how does food work as an environmental cue for the circadian rhythm of your organs?^​10​

• The first calories of the day start your digestive processes. 
• And this process continues around two to three hours after you consumed the last calories of the day. 
• A process that, for most, lasts more than fifteen hours every single day. 

What do your organs do when they are not involved in the digestive process? Only then can they repair and rejuvenate themselves. And with a strong circadian rhythm, you would allow your organs at least as much time to repair and rejuvenate themselves as they have to work on your digestive processes.

Are you interested in all the (health) benefits of using the timing of when you eat to your advantage? You can find out all about it in this post: “When Is the Best Time to Eat – Based on Your Circadian Rhythm.”

But here’s the problem: You do most likely eat for too long and too late:^​10​

• If you are like most people, then you believe that you consume your calories in a twelve-hour window (and are not counting any drinks or late-night snacks).
• But you actually consume calories for fifteen hours or more. Add the three more hours that your organs need for digestion after your last calories came in and they end up working for eighteen hours or more.

This means that you make your organs work for more than seventy-five percent of every day. Flip this coin and you see that you are only giving your organs less than twenty-five percent of the time to repair and rejuvenate. Every single day.

Check out tips #10 and #11 in this post about “How to Get Your Circadian Rhythm Back on Track” for practical information about how you can use food as an environmental cue to set your organs up for a strong circadian rhythm.

To sum it up, food is a powerful environmental cue for the circadian rhythm of your organs. When you start eating, your organs have to stop their rest and rejuvenation processes and start their digestive processes. This continues until two to three hours after you stopped eating. And you most likely eat for too long and too late, cutting short the rest and rejuvenation processes of your organs.

Exercise

Why Exercise Is the Third Most Powerful Environmental Cue to Entrain Your Circadian Rhythm

The timing of when you exercise and move is a distant third most powerful environmental cue to entrain your circadian rhythm. But exercise and movement still have a powerful effect on your circadian rhythm.

On the one hand, you can use exercise to strengthen the circadian rhythm of your muscles.  And exercise during both the morning and the late afternoon/ early evening is especially beneficial to strengthen their circadian rhythm. Which then allows for improved musculoskeletal health (including maintenance and function).^​11,12​

Check out tip #12 in this post about “How to Get Your Circadian Rhythm Back on Track” for practical information about how you can use exercise and movement as a zeitgeber to set your muscles and tissues up for a strong circadian rhythm.

On the other hand, you can also use your circadian rhythm to find out the best time for you to exercise:^​13​

• In short, exercise in the morning to set you up for a great start to the day.
• And exercise in the late afternoon/ early evening to benefit from when you are at your daily peak performance level.

Depending on the purpose and motivation for you to exercise, you can find out the perfect timing for you to exercise in this post about “When Is the Best Time to Exercise – Based on Your Circadian Rhythm.”

Other Environmental Cues

Other Environmental Cues and Their Impact On Your Circadian Rhythm

Finally, there are other environmental cues that either used to impact your circadian rhythm, were thought to impact it (but actually don’t), or even disrupt it. Let’s have a look at a few of these here.

No Impact

Environmental Factors That Don’t Impact Your Circadian Rhythm

The ambient temperature used to be an environmental cue for us. Not only for our daily circadian rhythm, but especially for our yearly circa-annual rhythm. The fluctuations of ambient temperatures together with daylight used to signal our bodies what time of the 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 ambient temperatures and daylight. Accordingly, this circa-annual rhythm has become weaker than ever.^​14​

According to the social zeitgeber theory, your social life – or better your social life stress – can indirectly act as an environmental cue that then disrupts your circadian rhythm. Here is how it goes: Your life stress leads to mood episodes that lead to disruption in your social routines that then lead to disruptions in your circadian rhythm. And while your social life indeed indirectly impacts how you interact with your three main environmental cues (light, food, movement) there is only limited data supporting this social zeitgeber theory so far.^​15​

There are anecdotal beliefs and folk wisdom that the moon can act as an environmental cue. Especially for your mood cycles and mental health. However, there is no solid evidence that the moon in any way acts as an environmental cue for you (for a few animals that live close to the coastlines it does). What influences people may not be the moon itself, but the placebo factor of their belief in it.^​16​

Disruption

Environmental Factors That Disrupt Your Circadian Rhythm

Some environmental cues don’t help to entrain your circadian rhythm but simply disrupt it in one way or another.

Here are a few environmental cues that are known to disrupt your circadian rhythm:

• Alcohol as a zeitgeber disrupts the timing of many of your physiological, endocrine, and behavioral functions. Remember that your circadian rhythm optimizes those timings? Well, alcohol disrupts those timings.^​17​
• Caffeine as a zeitgeber disrupts your circadian rhythm by delaying your metabolic functions. In addition, its wakefulness-promoting and sleep-disrupting effects further disrupt, yet more indirectly, your circadian rhythm.^​18​
• Nicotine as a zeitgeber disrupts your circadian rhythm by phase advancing it. This basically makes your body think that it is later than it actually is. And it has to speed up what it is currently doing to catch up.^​19​

And yes, alcohol, caffeine (especially in the form of coffee), and nicotine (especially from tobacco) are the three most widely consumed “psychoactive substances” aka drugs in the world.^​20​

Let’s phase shift now to how you can entrain aka strengthen your circadian rhythm with the three most powerful environmental cues.

Entrainment Hacks

How to Use the Top Three Environmental Cues to Your Advantage to Entrain Your Circadian Rhythm the Right Way

Why are we talking about helping you to entrain aka strengthen your circadian rhythm with your environmental cues here? Because, thanks to our modern environments, there are four problem areas that most likely prevent you from living aligned with your circadian rhythm. 

And those are connected to either your daily light exposure or your eating timings – which are the two most powerful environmental cues that help align your circadian rhythm(s):

• The first problem is that you don’t receive high enough light intensities during the day.
• The second problem is that you do receive too much light intensity during the evening and night.
• The third problem is that the light you receive during the evening and night is too high in the blue-light spectrum.
• The fourth problem is that you eat for too long and/ or too late.

You can get a full understanding of each of the four problem areas as well as the tips to overcome these in this post: “How to Get Your Circadian Rhythm Back on Track”

Still here? Ok, let’s then have a quick look at what you can do about each of these problem areas:

Problem 1: You don’t get enough light during the day

Tip #1 Spend at least two hours outdoors during the first half of every day
Tip #2 Stay as close to windows as possible if you are indoors
Tip #3 Take artificial light showers during the day if needed
Tip #4 Don’t wear sunglasses (if you don’t spend the whole day outside)
Tip #5 Spend a weekend in nature

Problem 2 & 3: You get too much light & blue light during the evening and night

Tip #6 Adapt your home lighting for the second part of the day
Tip #7 Reduce blue-light emissions from your screens
Tip #8 Use blue-light filtering glasses
Tip #9 Avoid any (blue) lights at night

Problem 4: You eat for too long and/ or too late

Tip #10 Stop eating early enough in the evening
Tip #11 Eat for fewer hours every day

“Bonus” Problem: You don’t exercise at the right times

Tip #12 Use exercise to help align your circadian rhythm

You can get a full understanding of each of the four problem areas as well as the tips to overcome these in this post: “How to Get Your Circadian Rhythm Back on Track”

Personal Experiences

My Personal Experiences

Knowing that my circadian rhythm needs environmental cues and can at the same time be disrupted by those (thanks to our modern environments) has helped me to use them in my favor.

In the mornings, directly after I wake up,  I always try to go outside and do some exercise outside. My favorites are going for an easy run or walk and just soaking in the morning sunlight And I can nearly immediately feel the positive effects this has on me. Even if it is just for ten or twenty minutes.

In the evenings, I always try to stop eating very early. I do only eat for a very few hours around noon. Mostly a few meals back-to-back or sometimes I just eat once. I still eat a lot, but I start late and finish early. This has especially helped me to achieve a continuously high sleep quality. And I normally don’t even need an alarm clock the next morning to wake up again.

What can you take away from this? Just being aware of the most powerful environmental cues is a great first step. But I hope that I was able to show you some practical examples of how you could use your knowledge of those environmental cues to your advantage. To entrain your circadian rhythm.

Key Takeaways

Key Takeaways

There are three key takeaways that I want to share with you that all help you to use environmental cues to your advantage to entrain and ultimately strengthen your circadian rhythm:

1. Your circadian rhythm is not exactly twenty-four hours long and your body needs environmental cues to align your circadian rhythm with your external exactly-twenty-four-hour-long day. This process is called entrainment.
2. The three most important environmental cues that entrain your circadian rhythm are as follows:
   • The by far most powerful environmental cue is your daily light exposure.
   • The second most powerful one is the timing of when you eat.
   • In a distant third place is the timing of your exercise & movement.
3. Thanks to our modern environments, you need to need to actively manage those environmental cues:
   • Increase your natural light exposure as much as you can during the day & reduce your artificial light exposure during the evening and at night. 
   • Don’t eat for too long and/ or too late.
   • Exercise during the morning or late afternoon/ early evening.

And now back to you: Have you already identified how you can best use those environmental cues to your advantage? And if so, how would you make your changes a daily habit?

Stay fit,

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

References

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