Thanks to our modern environments, you have already changed your chronotype without knowing it. Why? Because there is one external factor that your chronotype follows. Natural sunlight. But in our modern environments, you are mostly shielded from sunlight. And that changes your chronotype. It makes your chronotype later. And also weakens your circadian rhythm – but that’s another story.

How can you change your chronotype? You cannot change most of the parts that influence your chronotype, like your genes, age, sex. However, there is one part that you can change: your daily light exposure. Through optimizing your daily light exposure, you can change the expression of your chronotype to your advantage.

Read on to get a full understanding of:

• What your chronotype is in the first place
• Which factors determine your chronotype
• How to change your chronotype (at least the part you can)
• Why your daily light exposure is the key to change your chronotype
• How long it takes to change your chronotype
• My personal experiences and your key takeaways

Let’s get started with a basic overview of what your chronotype is. And then we’ll directly go into the factors that determine it and how you can change these. (Ok, just one of these). But first things first.

What Is Your Chronotype

What Is Your Chronotype in the First Place

Let’s get started with an overview of what your chronotype is. And then break down all the factors that influence your chronotype to see which of these you can change.

The name chronotype is a combination of the Greek “chrónos,” which means “time”, and “type.” It basically means that your chronotype is your “time type.” Your chronotype as a “time type” refers to your sleep-wake-cycle and is the most apparent expression of your internal time.^​1​

Your chronotype controls when you want to go to sleep and when you wake up thereafter. But your sleep-wake cycle is just one aspect of your internal time. Even though it is the most obvious aspect.

To be more precise here, it is actually your circadian rhythm that is the expression of your internal time. And your chronotype – as your sleep-wake-cycle – is just the most obvious part of your circadian rhythm. Your circadian rhythm also controls all your other body functions. And also they are cyclical but in less apparent ways.

You can read more about what your circadian rhythm is or about how your circadian rhythm works.

Chronotypes are individual to each person—some people are earlier and some are later chronotypes—and follow a normal distribution, like nearly everything in nature. However, chronotypes are commonly oversimplified and focus either on very early chronotypes (e.g., larks) or very late chronotypes (e.g., night owls). But our common differentiation only focuses on the extremes of chronotypes. They neglect the majority of the population who fall somewhere in between those two extremes. Just like you.^​2​

You can read all about it here: “What Are Chronotypes and How to Find Out Yours”

Ok, enough general information about chronotypes. You are reading this post because you want to know if and how you can change your chronotype. To answer this, let’s have a look at which factors determine your chronotype.

Which Factors Are Important

Which Factors Determine Your Chronotype

First off, there are quite a few factors that determine your chronotype. And while you can’t control most factors, there’s one that you can. And this one has a powerful effect on you:

Factors that you can’t change:	Factors that you can change:
Your genes	Your daily light exposure
Your age
Your gender
The season you were born
The current season

Ok, you can’t change most of the factors that determine your chronotype. But it’s still important to understand how they impact your chronotype. So let’s start with a quick overview of these first:

• Your genes explain one big part of your chronotype. You were already born with the tendency to be either a rather late or a rather early chronotype. (Hur et al., 1998; Koskenvuo et al., 2007) And your genes also influence how well you are able to handle sleep pressure – which then, more indirectly, influences your chronotype.^​1​
• Your age explains another big part of your chronotype: You start as a very early chronotype. Then you gradually become later until you hit your peak latest chronotype around the age of twenty. From this turning point on, you continually become an earlier and earlier chronotype again.^​2,3​
• Your gender subtly impacts your chronotype. Your chronotype is during most of your life slightly earlier if you are a woman and slightly later if you are a man.^​3,4​
• The season you were born also impacts your chronotype. If you were born in a season with more natural daylight (like spring and summer) then you are more likely to be a later chronotype. And if you were born in a season with less natural daylight (like winter) then you are more likely to be an earlier chronotype.^​5​
• The current season has a big influence on your chronotype. In summer, you tend to become an earlier chronotype. And in winter, you tend to become a later chronotype. Both because of the availability of and your exposure to natural light.^​6​

But there’s one factor that you can change:

• Your daily light exposure is one of the biggest factors that influence your chronotype. Or, to be more precise, your daily light exposure impacts the expression of your chronotype. In short, if you get enough natural light then your body can align your chronotype to your external day. And your body can also optimize the timing of all your daily functions.^​7​

Unfortunately for you, you don’t receive the right (aka natural) light exposures at the right time. But luckily, this is the one area that you can control. So let’s have a look at what that means.

How to Change Your Chronotype

How to Change Your Chronotype

You can change your chronotype. And your daily light exposure is the factor to do so. But that might be different than you expect. Because you can only change your chronotype to some extent. And that extent is usually determined by how misaligned you currently are. Because of your daily light exposure. That you get (or better, don’t get) because of the modern environments you live in.^​8​

So, to help you change (aka align) your chronotype, let’s have a look at three things:

1. What kind of daily light exposure does your body expect and need?
2. What kind of daily light exposure does your body typically get?
3. How can you improve your daily light exposure?

The Light You Need

What Kind of Daily Light Exposure Does Your Chronotype Need

Let’s take a step back and see how your light exposure determines your chronotype. This will also make it easier to see how you can change it.

In short, you have a central internal clock in your brain that uses light information to align your internal time with the external day. For this, your eyes have special receptors that send the time of day information – based on the light they receive – directly to your internal clock. Based on your internal time, your body then optimizes the timing of all your daily functions. This is called your circadian rhythm. And one part of your circadian rhythm is your sleep-wake-cycle. This is your chronotype.^​7​

Now, your internal clock has three basic options to align your internal time with the light information it receives. And those three options depend on both time and intensity:

When do you receive light?	How does it affect your internal time?
Light in the first part of the day…	…speeds up your internal time.
Light during the middle of the day…	…leaves your internal time as it is.
Light in the evening and at night…	…slows down your internal time.

Why does your internal time – and with this your chronotype – need to be aligned with your external day? Because your internal day is not exactly twenty-four-hours long. But your external day is. And your external light information is what aligns your internal day with your external day.

You can read all about it in this post: “How Does Your Circadian Rhythm Work”

But here’s the thing: Your body expects natural light. And this has two important properties

1. Natural light intensity is crazy high during the day but very low in the evening and virtually zero at night.
2. Natural light is high in blue-light rays during the day, but not in the evening and at night.

The problem is that your daily light exposure is different from what your body expects and needs. And this also impacts your chronotype. Or shall I better say it changes your chronotype?

The Light You Get

What Is the Problem With Your Daily Light Exposure

Ok, time for a quick recap. Your daily light exposure is one of the biggest factors that influence your chronotype. And it is the only one that you can change.

But in your modern environments, you are mostly shielded from natural light and exposed to artificial light. You spend much less time outside and much more time inside than your ancestors. Especially if we are working indoors. And this heavily affects your daily light exposure.^​2,8,9​

The first problem is that you most likely don’t receive high enough light intensities during the day. In this way, you don’t allow your body to optimize the timing of all its daily functions. The light signals are too weak to help your body align your internal time to the external time of day. Your internal time simply doesn’t speed up as much as it would need. As a consequence, you become a later chronotype.

The second problem is that you most likely do receive too much light intensity during the evening and night. And the third problem is that this light is most likely too high in the blue-light spectrum. In this way, you don’t allow your body to prepare for the night. And the light signals are too strong so that your body slows down your internal time. You receive light when your body doesn’t expect it anymore. Your internal time slows down much more than needed. As a consequence, you become a later chronotype.

What is the consequence for you? Well, you’ve seen that you become a later chronotype. But then, your body also cannot optimize the timing of your functions. And the two most apparent ones for your chronotype are your daily hormone levels of cortisol (the hormone that energizes you) and melatonin (your sleep hormone).^​10,11​

• In the morning, your body doesn’t stop the production of melatonin and doesn’t ramp up the production of cortisol. As a consequence, you still feel overly tired when waking up and lack energy for the day.
• In the evening, your body still produces too much cortisol and doesn’t start to produce enough melatonin yet. As a consequence, you feel too energized to sleep and you also reduce your sleep quality.

And those are just the problems connected to your chronotype. Also, your circadian rhythm becomes weaker, which means that your body cannot optimize your daily functions as it should.

Want to get the big picture? You can read the full story here about “Why Is the Circadian Rhythm So Important for You.”

The Changes You Can Make

What Is the Problem With Your Daily Light Exposure

Now, let’s have a look at how you can practically change your chronotype. From what you have seen above, there are three problems that you want to overcome to change your chronotype so that it aligns with your external day. This change would strengthen your circadian rhythm and your chronotype. And with it would come a lot of other health and performance benefits for you.

You have seen above that there are three basic problems around your light exposure during the day and in the evening/ at night. The following is a summary of how you can change your daily light exposure to change your chronotype. Or, to be more precise, to get your circadian rhythm back on track. Which would then also change and align your chronotype, which is the most obvious part of your circadian rhythm.

You can read the full story, including all practical details, in this post: “How to Get Your Circadian Rhythm Back on Track”

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

But there is also the other option to specifically change your chronotype to become either earlier or later. This could help you overcome problems that you might have due to shift-work, jet lag, or any other social reason.

In this case, you can use the same principles as we have seen above:^​9​

• Light in the first part of the day advances your internal clock. This effectively makes you an earlier chronotype.
• Light in the evening and at night slows down your internal time. This effectively makes you a later chronotype.

Now, how can you strategically use light to change your chronotype? If you want to be able to fall asleep earlier in the evening, then get as much (natural) light as you can get in your morning. And if you want to be able to stay awake longer, then get as much light in the evening and at night.

But be aware, that getting light (especially if it is high in blue-light-rays) in the evening also disrupts your circadian rhythm. And that comes with its own set of challenges. Starting with  reduced sleep quality, reduced performance, and higher risk for all kinds of diseases.

Again, I can recommend you to check out this post “Why Is the Circadian Rhythm so Important for You” for more information about this and related issues.

How Long Does It Take

How Long Does It Take to Change Your Chronotype

How much you can change your chronotype depends on how much “potential” you have to change. Let me explain.

Just imagine you live fully aligned with your chronotype and are only exposed to natural sunlight – outside and all day long. In this case, you already live at your full potential and don’t need to change anything for your chronotype. Or imagine the other extreme, where you are not exposed to any light or are exposed to constant light. In this case, you have a lot of potential to change. And the change would take that much longer.

But the most likely case is that you, like the majority who live in our modern environments, don’t get enough natural light during the day and too much artificial light at night. So let’s take this as our benchmark.

How long exactly would the change take? The answer is that it still depends. It depends on how intensive your light exposure is. Let’s have a look at three well-studied cases:

1. You can change (advance) your chronotype on average by two hours if you spend one week in nature (aka if you go camping). And that change is even more if you are a later chronotype.^​12​
2. You can change (advance) your chronotype by one to one-and-a-half hours if you spend one weekend in nature (camping was studied again). Also, this change is greater if you are a later chronotype.^​13​
3. You can change (advance) your chronotype by one hour if you receive at least two hours of natural light during the first part of the day. Again, this change is greater for later chronotypes.^​8​

What these studies show you are two things. One, you don’t get enough natural light exposure. As a result, your chronotype gets later. Two, this effect is greater for you if you are a later chronotype.

But it’s not just about aligning your chronotype to your external day. It is about aligning and strengthening your whole circadian rhythm (of which your chronotype is just one part). And about all the health and performance benefits that come with allowing your body to optimize the timing of all your daily functions.

Personal Experiences

My Personal Experiences

Do you remember how you can advance your chronotype by spending time in nature? Or better by being exposed to natural sunlight all day long? Well, that is exactly what I did when I did a four-month-long “experiment” when I lived in a small Kenyan town called Iten to train with some of the best runners in the world.

Besides running, one of the biggest differences was my daily light exposure. We started running early in the morning, just when the sun came out. Rested and relaxed with direct or indirect sun exposure during most of the day. And then ran again in the afternoon. I was basically exposed to the sun all day long (and never used as much sunscreen before in my life).

As soon as the sun went down, my light exposure also went down with it. Just to paint a picture here: There was only one main street with spare lighting. The rest of the town was more or less lit up by the night sky.

How did my chronotype advance? Quite quickly, it advanced by about two hours. I naturally woke up some time after 6 am, just before the sun came out. And after the sun went down twelve hours later, it didn’t take me too long to feel ready to go to bed.

And the sleep I got every night was one of the best ever. I fell asleep virtually as soon as I went to bed and early the next morning I woke up full of energy and ready to start the day.

Now, while it’s not the most practical to completely change my environment to align my chronotype, there was one big thing that I took away from this time. And that is doing exercise outside with natural light, directly after waking up.

For me, that could be anything from running or cycling to just going for a walk. As long as I’m moving my body and receiving plenty of sunlight, I can feel a positive effect on my body. It always feels like the best start to the day. And it helps me align (aka advance) my chronotype also at home.

Key Takeaways

Key Takeaways

Finally, there are four key takeaways that I want to share with you about your chronotype and how you can change it:

1. Your chronotype is the most obvious expression of your internal time and part circadian rhythm. It controls when you want to go to sleep and when you wake up thereafter. The name chronotype is a combination of the Greek “chrónos,” which means “time”, and “type.”
2. You can’t change most of the factors that determine your chronotype, like your genes, your age, your gender, the season you were born, or the current season.
3. The one factor that you can change is your daily light exposure.
   • Natural light in the first part of the day advances your internal clock. This effectively makes you an earlier chronotype.
   • Artificial light in the evening and at night slows down your internal time. This effectively makes you a later chronotype.
   • Your chronotype is chronically too late because you don’t receive enough natural light during the day and too much artificial light in the evening and at night.
4. You can change your chronotype. Here are two of the best-studied ways:
   1. During the week: Spend at least two hours outside, exposed to natural sunlight. 
   2. On the weekends: Ideally, spend the whole time in nature. Otherwise, spend as much time outside as possible.

And now back to you: Reflecting on your chronotype, do you have problems falling asleep and/ or waking up during the week? If so, what could you do to change that? If not, (congrats btw!) what has helped you to reach that point?

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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