Chronotype vs circadian rhythm

Answering a reader question

Do you follow the sun? The moon? Both? Neither? In today’s post, we’ll be investigating all the activity archetypes and how to use circadian biology to waylay your own personal Ragnarok.

Today’s post was inspired by longtime community member and friend

Jani Konjedic

, who writes Conquering Burnout. Jani asks:

Are you familiar with Dr. Michael Breus' work about sleep chronotypes? I find his ideas very interesting and they relate to me very much. 

I was wondering how much different personalities and chronotypes affect circadian rhythm. How much does circadian rhythm change from individual to individual based on their own personality and chronotype? Ex if someone is a morning person or a bear vs a night person or a wolf?

Keep reading for my response to Jani’s question.

For those who may not be familiar, the idea of chronotype is the idea that individuals have natural tendencies towards different kinds of schedules. We have probably all observed this in ourselves and others! Some people tend to be chipper in the mornings, while others seem to come alive in the evening. So, is this nature or nurture, or both?

Check out Dr. Breus’ website to learn about these chronotypes: https://sleepdoctor.com/sleep-quizzes/chronotype-quiz

Dr. Breus divides people into 4 archetypes, and you can find his popular chronotype quiz here (I got lion):

• Lion: typical morning type

• Bear: (most common, approximately 55% of all people) daytime type

• Wolf: typical evening type

• Dolphin: insomniac/restless type

Share your type and if you think it fits in the comments:

Something I find interesting from the world of biology is that across species, there emerge:

• Diurnal: daylight active

• Nocturnal: nighttime active

• Crepuscular: most active in the twilight hours of dawn and dusk, with subtypes of

  • Matitunal (dawn-only)

  • Vespertine (evening-only)

• Metaturnal/cathemeral: active whenever the best opportunities for eating, socializing, and mating exist (usually in seasonal patterns)

Most treat humans as diurnal, but some believe humans are metaturnal/cathemeral, which is what makes most sense to me.

Proponents of the chronotype concept suggest an evolutionary advantage to having people available to keep watch and work around the clock, which I also see as logical.

Furthermore, from my work, it’s no mistake or mismatch that our babies are born needing care around the clock, and I know all mothers are absolutely equipped to be able to provide such care.

So, what might it mean, from a circadian rhythm standpoint, to be one chronotype or another? To answer this question, I look again to biology. We know about humans that chronotype tends to shift across the lifespan, by sex, and by location with city-dwellers overall tending to have a later chronotype¹. Here are some of the known trends:

• Newborns take 2-3 years to develop a steady circadian rhythm

• Children tend to be morning type

• Teens tend toward a later chronotype (stay up later and wake up later)

• Through the reproductive years:

  • Women’s hormones lose their rhythmicity during the luteal phase of the menstrual cycle contributing to monthly variations in their sleep, digestion, mood, and energy (and also during pregnancy and lactation)

  • Men tend to have a more stable chronotype overall

• After menopause, women and men tend to have a similarly early chronotype

• At no stage of life have humans to be found to have a completely nocturnal activity pattern

Looking at the circadian hormone melatonin, here’s what that looks like:

And if you are interested in the research about melatonin and how to set a baby up for healthy rhythms across the lifespan, check out my post:

Your mother gave you your circadian rhythm

So what happens when a person is outside of the typical pattern of waking around sunrise, being alert across the day, and sleeping easily through the evening and night? This is where things get more murky (or interesting, depending on your perspective!).

For one thing, anecdotally, I personally know several people who thought of themselves as die-hard night owls (“wolves”), that became morning larks (“lions”, or at least “bears”) when they started changing their habits to better support their circadian rhythms.

At the same time, I also know someone with a diagnosed non-24 sleep disorder, who is predicted to never be able to keep a consistent schedule for any length of time.

When it comes to health and wellness, we know that adults with an evening chronotype tend to have a higher number of physical and mental health problems but that the research has not been able to identify a causal pattern².

• Does eveningness cause health problems?

• Do health problems cause eveningness?

• Does a third factor cause both eveningness and health problems?

And this is partly because it is unethical to do causality-proving research on humans, and partly because this whole field of study is relatively new. Here’s a timeline from researchers at the University of Texas³:

Did you know most of today’s indoor and outdoor lighting regulations were created before the discovery of the SCN?

And to further confound our understanding, much of this research has been conducted on nocturnal lab animals, namely rodents. While it was assumed nocturnal and diurnal animals worked largely the same, only with opposite schedules, new research is indicating a fundamental difference in how the individual neurons of diurnal animals act⁴.

Imagine being woken up at 3 a.m. to navigate a corn maze, memorize 20 items on a shopping list or pass your driver's test.

According to a new analysis out of West Virginia University, that's often what it's like to be a rodent in a biomedical study.

Source: Science Daily

Thus, now that we are learning more and more about the circadian rhythm as well as inter-species variations in circadian regulation mechanisms, we will likely be seeing new protocols in research and new discoveries about applications of research to real life. Many things we thought to be true/false based on research done under poor circadian conditions even be re-written in coming years!

Beyond the Bear chronotype

To get at a better understanding of possibilities beyond trying to fit everyone in the diurnal box—which clearly doesn’t serve the great number of people who aren’t naturally “bears” (and, as per my work, which also doesn’t serve families with infants in the home), I have leaned into the Navy’s research on circadian watchbills.

Since ships must operate around the clock and since sailors agree to giving the Navy complete control over their individual schedules while at sea, Naval researchers have been able to control and experiment with rhythm and schedule to a unique degree.

“Pretending to be superhuman is very dangerous...It is time to critically reexamine our love affair with stoic self-denial.  If an adversary can turn our commanders into sleepwalking zombies...the adversary has done nothing fundamentally different than destroying supplies of food, water, or ammunition. But we must stop doing it to ourselves and handing the enemy a dangerous and unearned advantage" - Jonathan Shay

In terms of stretching human capacity around the clock, the work by the Navy has elucidated some unique hard and fast rules about circadian rhythmicity I haven’t seen anyone else talk about:

1. Regular hot meals, because everyone, no matter their schedule, needs at least one big and consistent meal every day to keep in a healthy circadian rhythm.

2. Quiet, because everyone, no matter their schedule, needs quiet while they rest.

3. Sleep windows that overlap (but don’t necessarily match) the natural darkness.

4. Daytime naps of either 30 minutes OR 2+ hours to compensate for short nighttime sleep windows.

5. Important meetings should be scheduled in the afternoon, because it is the time when nearly everyone can be somewhat alert (unlike morning, evening, and nighttime, which are times when a significant amount of people will be significantly unhappy—or even unable—to be alert at that time).

6. If doing a massive schedule shift (such as moving into a semi-night shift or changing time zones), ideally spend at least 6 weeks in the new schedule before changing it up again to maximize the body’s ability to adapt before being thrown into circadian chaos again. Or, at minimum, allow one day per hour time shift to adjust.

And in all cases, they recommend daily physical activity, bright light in the day, and limited artificial blue light before bed (remember blue light doesn’t have to look blue—it’s actually what makes artificial light look “white” to us). These last few tips would be anyone’s standard circadian rhythmicity tips. You can read more about these rules, their research and see example 24-hour schedules at the Crew Endurance website, where they have the compelling motto: “Sleep is a Weapon; A Clear Mind is a Combat Edge.“ Check it out here.

My opinion after assimilating and testing all of this knowledge:

Any schedule is valid as long as the environment is in sync with local solar time and it feels good to you!

The trick is carving out a unique work and life schedule and environment that fits your needs.

For example, many people may think that since I am naturally a morning-type, life would be easy for me. What they may not know is I have only ever had one full-time job that lasted longer than 3 months (and that longer job only lasted slightly over one year, during which time I actually quit twice!). And while I was an honor’s Biology student, I dropped out 4 times before I actually got my degree.

Morning types, yes, wake up ready, but can wane early in the day compared with “Bears” who can go all day. It took many efforts to get to know my own rhythms, especially as a woman going not only through the menstrual cycle, but also being pregnant and breastfeeding 4 times.

And this is why I named my publication (warmer) Brighter Days, (cooler) Darker Nights.

I am proof you can break free from trying to fit yourself into the Bear schedule if you want (or need). And in doing so, you can also still keep your physical and mental vitality—maybe even more so that when you were trying to fit in.

Yes, it takes persistence, yes it takes consistency, and yes, it takes insistence and urgency. Creating an alternative environment and schedule takes work, but even in today’s world, it is possible if you really want it.

How do you think your circadian health is? Take my new quiz to see what I might say!

1. Roenneberg, T., & Merrow, M. (2007). Entrainment of the human circadian clock. Cold Spring Harbor symposia on quantitative biology, 72, 293–299. https://doi.org/10.1101/sqb.2007.72.043

2. Walker, W. H., 2nd, Walton, J. C., DeVries, A. C., & Nelson, R. J. (2020). Circadian rhythm disruption and mental health. Translational psychiatry, 10(1), 28. https://doi.org/10.1038/s41398-020-0694-0

3. Rijo-Ferreira, F., Takahashi, J.S (2019). Genomics of circadian rhythms in health and disease. Genome Med 11, 82. https://doi.org/10.1186/s13073-019-0704-0

4. Andreatta, G., & Allen, C. N. (2021). How neurons adjust to diurnality. eLife, 10, e74704. https://doi.org/10.7554/eLife.74704