Here is a concise explanation (and a link to a great podcast episode if you’re interested in more information) from a post on the Bulletproof blog:
Your circadian rhythm — your brain’s sleep-wake cycle — determines when you’re alert and when you’re sleepy over a 24-hour period. It’s the internal clock that your brain uses to signal when to release certain hormones.
While working with insomnia patients, Dr. Breus observed that everyone’s circadian rhythm is slightly different. (He details his fascinating findings, particularly about so-called insomniacs, on an episode of Bulletproof Radio.)
Based on morning and evening preferences, he identified four different chronotypes, or circadian rhythm personalities, and then associated each one with an animal whose sleep-wake habits best mirrored them.
When Breus switched up his patients’ daily routines to accommodate their sleep chronotype, their productivity soared and several sleep issues resolved.
Thus, circadian rhythm and chronotype are not the same, but they are intrinsically related. We all have a circadian rhythm, but our circadian rhythms differ. These differences are explained by our individual chronotypes.
Why does chronotype matter?
As mentioned above, knowing your chronotype may help you maximize your daily routine and efficiency.
Evolutionarily speaking, it was important for at least one member of a tribe to be to be 100% alert/awake at different times each day. If a certain group possessed only morning types, for example, it would be at higher risk of invasion in the evening since all group members would (likely) have fallen asleep early. Therefore, researchers have determined that:
. . . asynchronous periods of wakefulness provide an opportunity for vigilance when sleeping in groups . . . Chronotype variation and human sleep architecture (including nocturnal awakenings) in modern populations may therefore represent a legacy of natural selection acting in the past to reduce the dangers of sleep.
Currently, society is structured in a manner that favors morning types. Most jobs require workers to rise early and to be “on” around 9am. Most schools require students to begin learning around 8am. (The New York Times piece “Let Teenagers Sleep In” details why this is problematic.) However, many humans—adults, kids, and especially teenagers—are evening types. Since the status-quo favors early risers, evening types are often viewed as “lesser” and/or “abnormal.”
When considering the reality that both morning and evening types were valued as beneficial and necessary in tribal societies, society’s favoritism of morning types has led neuroscientists to advocate for evening types. If you’re one of the lucky ones who can choose your own work schedule, you should not feel inadequate if you prefer to get a later start to the day. Or, if you’re an evening type (E-type) who’s forced to wake up early Monday through Friday, you should know that:
. . . E-types accumulate a sleep deficit during weekdays due to social and academic commitments and that they recover from this deficit during ‘free days’ on the weekend.
I am an evening type who anxiously anticipates lazy weekend mornings, but I’m often chastised for this. Now that I know my chronotype, I feel vindicated!
How do you know which chronotype you are?
Chances are you already know whether you’re a morning or evening type without taking a test, but sleep specialist Michael Breus, PhD, developed a free online quiz based on his research and best-selling book The Power of When. Breus more specifically categorizes morning and evening types into four groups: dolphins, lions, bears, and wolves.
After taking the quiz, you can use your newfound knowledge to consider the most optimal routine for your chronotype.
If the schedule of your current job and/or lifestyle doesn’t allow you to optimize your chronotype (mine doesn’t!), you can at least be mindful of your body’s natural inclinations in order to enhance your free time on weekends and vacations…without feeling guilty, weird, or lazy!
Even though chronotype matters, it’s not everything. Clean-sleep habits are also extremely important!
How I Embrace My “Wolf” (aka “Unfavorable By Society’s Standards”) Chronotype:
I’m a “wolf,” but I must wake up early each weekday morning (like most members of modern society) to get to work. Since I need to wake up so early, I also must force myself to sleep earlier than I’d like; it’s important to get a minimum of 7 hours of sleep each night! The key word in that sentence is “force”. It’s difficult for me to fall asleep early, so I end up accumulating “sleep debt.”
On weekends and vacations, I’ve learned to embrace my chronotype by staying up a little later, sleeping in, and tackling that unwanted sleep debt. I used to feel guilty and lazy after sleeping in, but now I realize that it helps me optimize my health. It’s great for every person to pinpoint his or her chronotype, but it’s especially liberating for us wolves who are pressured to conform to society’s early-riser standards!
Bottom line: Figure out your chronotype to maximize your efficiency, better understand yourself, and recognize whether or not you should catch up on sleep during weekends and vacations!
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