You are influenced by zeitgebers every single day. And if you know what zeitgebers are and how they impact you, then you can also use them to your advantage. Unfortunately, though, the default in our modern environments is that zeitgebers are not working to your advantage. So let’s change that. But first things first, let’s start with what zeitgebers are.

Why are zeitgebers and which are the most important ones for you? Zeitgebers are environmental cues that help your body to align your internal time – and with this your circadian rhythm – to your external twenty-four-hour day. Literally translated, zeitgeber means “time-giver.” The by far most powerful zeitgeber is light, followed by food and then exercise/ movement.

Read on to get a full understanding of:

• What zeitgebers are, what their purpose is, and why they are so important for you
• What the three for you by far most powerful zeitgebers are and how they impact your daily life
• What you are influenced by other zeitgebers too
• How to use zeitgebers to your advantage
• My experiences and your key takeaways

Let’s start with a big picture of zeitgebers. And because zeitgebers play such a vital role for your circadian rhythm, let me also include a basic overview of your circadian rhythm and their interconnection.

What Are Zeitgebers

What Are Zeitgebers

Now, to get the full picture of your zeitgebers, I need to give you some context about your circadian rhythm. Because the role of zeitgebers is to align your internal circadian rhythm to your external day.

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 perform everything it needs to do at the same time.

What are those functions that are under circadian control? Everything from your sleep-wake behavior, to your hormone levels (such as testosterone, cortisol, or melatonin), to your organs and tissues, your cognitive and physical performance, or even your immune system.^​1​

Find out all about it in this post “What Is the Circadian Rhythm and Why Do We Have One.”

There’s only one little “problem” with your circadian rhythm. It is not exactly twenty-four hours long like your external day. 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?)”

Now, how does your body align your internal circadian rhythm to your external day? Well, it uses cues from your environment about the external time of day. These external environmental cues are your “time-giver” and this is what the German word “Zeitgeber” literally translates to. In short, your body synchronizes your internal circadian rhythm with your external day with the help of zeitgebers.

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.”

And what are these zeitgebers? They are environmental cues that your body can use to set your time. The by far most powerful one is your light environment, followed by your food timings, and your exercise (and movement).

Their Purpose

What Is the Purpose of Zeitgebers

To understand why we need zeitgebers, imagine a world where you live without any external cues that could give away the time of day. Since light is by far the most powerful zeitgeber for you, imagine a world with constant light conditions. And no social obligations to follow.^​3​

What would happen to your circadian rhythm? Well, it would not align with the length of your external day. This is a condition where your circadian rhythm would be “free-running.” And your day would most likely be slightly longer than twenty-four-hours.

Find out all about your free-running circadian rhythm here: “What Is a Free-Running Circadian Rhythm (And How Long Is It)”

And in this condition – without zeitgebers to align your internal circadian rhythm to your external day – it would make sense for your circadian rhythm to be exactly twenty-four-hours long.

But you don’t live in an environment without any zeitgebers. And neither our ancestors ever had.

From an evolutionary perspective, there hasn’t been a strong enough pressure to develop an internal circadian rhythm that is exactly twenty-four-hours long. Because there have always been environmental cues – your zeitgebers – that would align your internal circadian rhythm to your external day.

And this is why you need zeitgebers. Without them, your circadian rhythm would follow its internal length and be out of sync with your external day. But with zeitgebers, you can align your internal circadian rhythm with your external day.^​4​

But there’s one problem. In your modern environments, you are not exposed to strong enough zeitgebers anymore.

Their Importance

Why Are Zeitgebers So Important

Here’s the thing: When your zeitgebers are strong enough, that alignment works out as it should. And you have a strong circadian rhythm that is able to optimize your daily functions. But when those zeitgebers are too weak – like in your modern environments – then also your circadian rhythm becomes weaker. And can’t fully optimize your daily functions.

Let’s have a look at how we have weakened our zeitgebers through our modern environments. Let’s have a look at three different times that you interact with daily: sun time, social time, and your internal time:^​1​

• Sun time is the time of nature. Your body receives visual feedback through the position of the sun in the sky and the respective sunray pattern.
• Internal time is the time your body thinks it is. For this, you have an internal biological clock. Through your biological clock, your body maps its internal time. And through its internal time, your body develops your daily rhythm – your circadian rhythm.
• Social time is the time you live by based on your environment and social commitments. This could be anything from work or study schedule to time commitments with friends and family.

Up until the nineteenth century, we lived in alignment with the movement of the sun. We used to be outside most of the day and get plenty of natural sunlight exposure. And we used to get up and go to sleep based on the sun.

But then, the industrial revolution came and we spent most of our days inside. And railways challenged our sun-time system, eventually leading to the introduction of international standard times in 1884^​5​. A system that we still use today.

The result? Working indoors shielded us from environmental cues such as natural sunlight or fluctuating temperatures. And we started living based on social time schedules, instead of following the sun time. Both dramatically decreased the effectiveness of our zeitgebers.

That’s why your zeitgebers are generally not strong enough to set you up for a strong circadian rhythm.

And what does that mean for your everyday life? Let me walk you through two hormones that drive your sleep-wake-cycle and that are under your circadian control. The hormones cortisol that helps you energize (but also has a bad reputation as your “stress” hormone). And the hormone melatonin that helps you sleep.^​6​

But you need a strong circadian rhythm to control those hormones to get you ready for the day. Even before you wake up, it stops the production of melatonin and ramps up the production of cortisol. And in the evening, this is the other way round.

The result of such a strong circadian rhythm? You do not have any issues falling asleep. And you are consistently getting a high quality, restorative sleep. You are waking up refreshed and full of energy. Without an alarm clock. And you also feel full of energy during the day.

Now, for a strong circadian rhythm, you also need to be exposed to strong zeitgebers. But most likely you are not. Most likely, your zeitgebers are too weak. Which is a key reason why you might have issues both falling asleep and waking up.^​7​

This was just one example of the importance of your circadian rhythm. You can read all about it here: “Why Is the Circadian Rhythm So Important for You”

Ok, now that I have shared what zeitgebers are, what their purpose is, and why they are so important, let’s go and have a look at them in more detail.

The Most Powerful Zeitgebers

What are the Most Powerful Zeitgebers

When you think about zeitgebers, there’s basically only three that you should think about. Why? Because those three are the most powerful for you. And if you are aligned with these, then you are also set up for a strong circadian rhythm. Starting with the by far most powerful one, these are:

1. Light
2. Food
3. Exercise

But there are still a few other zeitgebers that have (or used to have) an effect on you. And while some of these could disrupt your circadian rhythm, others can strengthen it.

Let’s have a look at the most powerful ones first and then at some of the others.

Light

Why Is Light the by Far Most Powerful Zeitgeber

Light is the by far most powerful and important zeitgeber for your circadian rhythm. In fact, light controls your central circadian rhythm, which then orchestrates all other circadian rhythms in your body.^​3,8​

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

In short, you have a central 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.^​4​

In this way, light acts as the environmental cue – your zeitgeber – for your central circadian rhythm. And your SCN can align your internal circadian rhythm with your external day. This process is called “light entrainment.”

And whatever light information your SCN receives, it has three basic options to align 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 a zeitgeber. And it expects massive amounts of light during the day and virtually nothing in the evening and at night.

This was the short version. You can read all about it in this post: “How Does Your Circadian Rhythm Work”

But here’s the thing: That’s very different in your modern environment:

• 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 “Get Your Circadian Rhythm Back on Track: The Ultimate Guide” for practical information about how you can use light as a zeitgeber to set yourself up for a strong circadian rhythm.

To sum it up, light is by far the most powerful zeitgeber for you. And through the time of day information you receive from light, you centrally set your circadian rhythm. And this central circadian rhythm synchronizes all your other circadian rhythms.

Food

Why Is Food the Second Most Powerful Zeitgeber

You have just seen that light is the by far most powerful zeitgeber. And also that it is vital for your central circadian rhythm that then synchronizes all your other circadian rhythms. But there’s more to it.

Just like light as a zeitgeber impacts your central circadian rhythm, food as a zeitgeber impacts the circadian rhythm of your organs. To be more specific, any calories consumed impact the circadian rhythm of your organs.^​9​

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

Why is food such an important and powerful zeitgeber for your organs? In short, because your body loves calories. Having been able to extract virtually all available calories has been an evolutionary advantage during times of food shortages. Simply because it was vital for survival. That might be different today in times of abundance, but that’s still how our bodies work.

So, when you consume any calories, your organs have to go through their digestive processes to ensure that they take up them all. And that also counts for any tiny snack or drink.

How does food work as a zeitgeber? 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.^​10​

What do your organs do when they are not involved in the digestive process? They can 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.

How long is this repair and rejuvenation period? Well, it depends on your eating habits:

• The last calories you consumed determine when your organs can start their repair and rejuvenation process. 
• The first calories coming in again stop this process. Your organs have to start processing these calories. Even if that means that they couldn’t finish their repair and rejuvenation processes.

Here’s the problem: You do most likely eat for too long and too late. 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.

That means that you make your organs work for at least 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 a zeitgeber to set your organs up for a strong circadian rhythm.

To sum it up, food is a powerful zeitgeber for 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 Is Exercise the Third Most Powerful Zeitgeber

The most powerful zeitgebers for you are light (by far the most powerful) and food. A distant third place is exercise. But exercise as a zeitgeber still has a powerful effect on you.

On the one hand, you can use exercise to strengthen the circadian rhythm of your muscles.  And it turns out exercise during both the morning and the late afternoon/ early evening is especially beneficial for your 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.

In this way, exercise directly impacts your muscle clock. And it turns out exercise during both the morning and the late afternoon can help you get your circadian rhythm back on track. And while morning exercise will set you up for a great start to the day, in the afternoon you are at your daily peak performance level. Both are great timings to exercise. And both help you get your circadian rhythm back on track.

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

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 Zeitgebers

What Are Other Zeitgebers

Besides those three most important zeitgebers that influence your daily circadian rhythm, there are also a few more. But these are way less powerful. And some used to be powerful enough but are not anymore (temperature), while others only have anecdotal evidence to be a powerful enough zeitgeber (the moon).

Let’s continue with zeitgebers for your daily circadian rhythm before we go into other natural rhythms and have a look at whether you are (still) affected by their zeitgebers.

First, there is the social zeitgeber theory. This theory makes a point that your social life – or better your social life stress – can indirectly act as a zeitgeber 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. Seems a little far fetched? Maybe, but at least the connection of your social routines, which directly involve all the three most powerful zeitgebers, and your circadian rhythm is well established. Either way, there is only limited data supporting this social zeitgeber theory so far.^​14​

Other zeitgebers 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.^​15​
• 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.^​16​
• 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.^​17​

But do you want to hear some good news? One study found that chocolate may act as a zeitgeber, able to help you to strengthen your circadian rhythm. A piece of chocolate for breakfast can help you to synchronize and strengthen your circadian rhythm right from the start. What’s more? Such a daily piece of chocolate can also help you overcome jet-lag or shift-work. It signals your SCN (your central circadian clock) the start of the day and accelerates the alignment of your internal circadian rhythm with your external day. Chocolate in the evening, however, has the opposite effect.^​18​

Next to the daily cycle – because of which we have our circadian rhythm – there are three other natural cycles. And we are also affected by those other natural cycles, besides the tidal cycle (since we neither evolved in the ocean nor at its coastlines – at least not in the last few million years):^​1​

Cycle	Length	Rhythm
Tidal cycle	12.5 hours	Circa-tidal rhythm
Daily cycle	24 hours	Circa-dian rhythm
Lunar cycle	29.5 days	Circa-lunar rhythm
Annual cycle	365.25 days	Circa-annual rhythm

We also used to have a significant circa-annual rhythm. And our zeitgebers for this were both daylight and ambient temperatures. Those signaled 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. Accordingly, this circa-annual rhythm has become weaker than ever.^​19​

There is a belief that the moon is a zeitgeber that can impact your mood cycles and mental health. But this belief does not go beyond folk wisdom and anecdotal evidence. There is no solid evidence that the moon in any way acts as a zeitgeber 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.^​20​

How to Use Your Zeitgebers

How to Use Zeitgebers to Your Advantage

In general, there are four problem areas that most likely prevent you from living aligned with your circadian rhythm. And those are connected to either your light exposure or your eating timings – which are the two most powerful zeitgebers that help align your circadian rhythm(s):

1. The first problem is that you don’t receive high enough light intensities during the day.
2. The second problem is that you do receive too much light intensity during the evening and night.
3. The third problem is that the light you receive during the evening and night is too high in the blue-light spectrum.
4. 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: “Get Your Circadian Rhythm Back on Track: The Ultimate Guide”

Now you have seen the four biggest problems that disrupt your circadian rhythm and how they are connected to your two most powerful zeitgebers. So let’s 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: “Get Your Circadian Rhythm Back on Track: The Ultimate Guide”

Personal Experiences

My Personal Experiences

What has especially helped me to strengthen my circadian rhythm is to focus light and exercise as a zeitgeber in the morning and food as a zeitgeber in the evening. To be clear, your zeitgebers will affect you at any time of the day. But you can manipulate them to your favor. At least that’s what has helped me a lot. Let me explain.

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

So, what are those positive effects? I feel much more energized. And all my sleepiness vanishes. Even more, that already happens as soon as I wake up, just as if my circadian rhythm prepares me for it in anticipation. And with a strong circadian rhythm, this is actually what happens: Your circadian rhythm stops the production of my sleep hormone melatonin just before I wake up and ramps up the production of the hormone cortisol to energize me for the day.

In the evenings, I always try to stop eating very early. I used to do intermittent fasting where I ate from noon to 8 pm. And I was happy with it. But then I did a ten-day fast at the beginning of the year. And this changed everything. After a few days, my sleep quality improved dramatically and, at the same time, I needed far less sleep. And I loved it.

Now, I do only eat for a very few hours around noon. Mostly a few meals back-to-back. I still eat a lot, but I start late and finish early. Or sometimes just eat once. Unfortunately, I haven’t been able to achieve such high levels of sleep quality as during the fast. But, as compared to my eating habits before the fast, my sleep quality has significantly improved.

What can you take away from this? Just being aware of the most powerful zeitgebers is the first step. But I hope that my personal experience also showed you some practical examples of how you could use your knowledge of those zeitgebers to your advantage.

I can only strongly recommend you to give it a try and make use of your knowledge of which are the most powerful zeitgebers and how those zeitgebers impact you. Try to change one thing at a time and see which has the greatest impact and is most beneficial for you.

Key Takeaways

Key Takeaways

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

1. Zeitgebers are environmental cues that help align your internal circadian rhythm to your external day.
2. The by far most powerful zeitgeber is your light environment, followed by your food timings, and your exercise (and movement).
3. You can use zeitgebers to your advantage if you:
   • 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 your zeitgebers to your advantage? And if so, how would you make those 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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