Circadian rhythms, chronotypes & light

I usually wake up pretty early.

There’s something about being up and ready before the world gets going—I love that feeling. Most mornings, I spend some quiet time writing these newsletters and getting in a workout.

It’s never been too hard for me to wake up early. My body just seems to follow a natural rhythm that makes it feel easy.

But that also means that when Saturday morning rolls around, and I’ve been out late Friday night with friends, I still wake up early. I cant just sleep in to make up for it.

So I end up a bit tired and groggy, running on less sleep than I'd like.

Turns out, that’s because I’m an early chronotype. And this pattern isn’t exactly unique.

Have you ever felt that way? Or do you naturally prefer sleeping in?
- that might actually be worse for your sleep.

Today’s insights is mainly drawn from the scientific article: 

“Life between Clocks: Daily Temporal Patterns of Human Chronotypes”

Today's newsletter

• Takeaways:

• The study in a nutshell:

• What they did:

• What the authors found out:

• What can we learn from this study?

Takeaways:

🕵️‍♂️ Your tendencies to wake early or late, can be described as ”chronotypes”

The Munich ChronoType Questionnaire (MCTQ) offers a reliable way to assess individual sleep-wake patterns based on real-life behavior. It assigns you with a ”chronotype” that describes your decencies to be a morning person or an evening person.

☀️ Light exposure influences your biological clock

The more time people spent outside in daylight, the earlier they tend to sleep. Each additional hour of exposure to outdoor light correlates with roughly 30 minutes earlier sleep.

💵 Modern life creates sleep debt

With work og school starting ealy in the morning, especially late chronotypes suffer as their natual preference is to stay a wake later in the evening. Many people compensate by sleeping longer on free days, which a creates a pattern of mild sleep deprivation on weekdays.

The study in a nutshell:

Today’s study explores how modern life disrupts our natural sleep rhythms, and how we can understand our natural sleep preferences.

The authors used data from 500 people in Germany and Switzerland and introduced a new tool - the Munich ChronoType Questionnaire (MCTQ).

The MCTQ measures when people actually sleep on workdays versus free days and works as a tool that measures and classifies peoples natural tendencies in this regard.

The authors found that many people, especially ”late chronotypes” (evening people), build up sleep debt during the workweek and try to catch up on weekends.

The whole theme is based on the concept of Circadian rhythms, which is the body’s internal 24-hour cycles that regulates when we sleep, eat, and feel alert. These rhythms are controlled by clock genes and are tightly linked to how we manage energy and metabolism.

The brain’s master clock, located in the suprachiasmatic nucleus (SCN), uses light signals to keep the body’s many clocks in sync. Time spent outside in daylight therefor plays a role in determining peoples chronotypes.

So today’s newsletter is really all about explaining and giving an operational framework for why some people might walk around a bit sleep deprived. 

So let me ask you:

What they did:

The authors collected data from 500 people in Germany and Switzerland, aged between 6 and 65.

Participants completed the Munich ChronoType Questionnaire (MCTQ), which asked for detailed information about sleep and wake times, both during the workweek and on days off.

It also gathered estimates of how much time they spent outside in daylight and included a self-assessment of chronotype, ranging from extreme early to extreme late types.

A subset of participants also kept sleep logs for five weeks to validate the accuracy of their responses.

Midsleep - the halfway point between sleep onset and wake time - was used as a marker of each person’s internal clock. This allowed for a quantitative assessment of chronotype across a broad population.

What the authors found out:

The study showed that on average, participants slept about an hour longer on free days than on workdays while young individuals generally had the biggest differences.

This pattern suggests that many people accumulate sleep debt during the workweek and try to repay it on weekends.

The MCTQ worked, as it was shown that self-reported chronotypes-assessments matched well with measured sleep behavior.

Late chronotypes experienced the most sleep debt during the workweek, due to later bedtimes and fixed early wake times. They made up for this by sleeping longer on free days.

Early chronotypes, on the other hand, sometimes lost sleep on weekends due to social pressure to stay up later.

People who spent more time outdoors during the day with natural light exposure tended to fall asleep earlier. For every additional hour of daylight exposure per day, midsleep advanced by roughly 30 minutes.

What can we learn from this study?

In today's study, the authors found that the Munich ChronoType Questionnaire (MCTQ) successfully captures real-world sleep timing.

The measurement showed a strong correlation with both self-reported chronotype and sleep logs, and therefore appears to offer a precise and behaviorally grounded method for identifying chronotypes.

The original MCTQ, however, is a pretty long questionnaire. But luckily, the same authors later developed a shorter version that correlated very well with the original, as well as with some objective measurements of sleep and sleep timing.

Actually, I found a very interesting study showing that what I believe is the short version of the MCTQ - although it isn’t explicitly labeled as such - correlates very well with an objective measure of the midpoint of sleep.

Today’s main study describes how the timing of sleep is shaped by both biological, behavioral, and environmental factors, and how modern life often puts these factors in conflict.

Late chronotypes struggle with early work or school start times that dont match their internal clocks. As a result, they accumulate sleep dept during the workweek and compensate by sleeping longer on free days.

On the other hand, early types may loos sleep on weekends due to social pressure to stay up later.

For example, they might go out with friends and stay up way past their bedtime, yet still wake up pretty early the next day because of their internal clock - a struggle I recognize..

Interestingly, last week we found that prolonged insufficient sleep takes more than just one night to correct. For me, this suggests that especially late chronotypes are unlikely to fully “make up” for the sleep debt accumulated during the week over the weekend.

Light exposure was shown to be a major factor in sleep timing.

What I believe we can take away from this work is the importance of understanding our individual chronotypes and recognizing how they interact with our everyday lives to shape our weekly sleep patterns.

This understanding can provide a foundation for optimizing our sleep in a way that takes both workdays and free days into account.

By managing our schedules with our specific chronotype in mind - and using natural light exposure as the key synchronizer for our internal clocks - we gain a much better toolkit for ensuring we get the sleep we truly need.

Want to know your chronotype?

Go to our resource site - I’ve just added a chronotype assessment! You’ll find it under the “Assessments” section.

_{Disclaimer: The above is mainly based on the article “Life between Clocks: Daily Temporal Patterns of Human Chronotypes” by Till Roenneberg, Anna Wirz-Justice & Martha Merrow and aims to provide key takeaways and a condensed overview of its content. While the essence is drawn from the original article, some parts have been simplified or rephrased to enhance understanding. Please note that we at, OptiMindInsights or any other potential writers or contributors to our summaries, do not accept responsibility for any consequences arising from the use of this summary. The information provided should not be considered a substitute for personal research or professional advice. Readers are encouraged to consult the original article for detailed insights and references. The summary does not include references, but they can typically be found within the original publication. Always exercise due diligence and consider your unique circumstances before applying any information in your personal or professional life. We refer to the creative commons for reproducibility rights.}