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Have you ever woken up feeling extremely groggy or feeling like death for no apparent reason?

(It’s not like you went to an all-night rave the night before…or did you? 😅)

This might be due to your chronotype.

What is a chronotype?

Let’s first define some terms and build up to what a chronotype is.

All humans have internally built-in, genetically dictated biological clocks (made up of specific molecules) that dictate the timing of our circadian rhythm, both how long the rhythms are and their timing.

"Circadian rhythms are physical, mental, and behavioural changes that follow a daily cycle.” In Latin, the root “circa” means “around/approximately” and “diem” means “day”. These rhythms are mostly known as related to the sleep/wake cycle, but it also encompasses things like hormone production, body temperature, cell regeneration, brain wave activity, etc.

There has been debates about how long our internal clocks are, but a rigorous study by Czeisler and team at Harvard has found that "the range for normal, healthy adults of all ages to be...24 hours and 11 minutes ± 16 minutes.” They found that no matter what the people in the study did during the day, or when they went to bed or woke up, their “body temperature and hormones rose and fell on an average of 24 hours and 11 minutes” cycle.

However, despite us all having biological clocks/circadian rhythm that is roughly 24hr+ in its cycle, turns out that not all of our internal clocks are aligned perfectly to the sunrise/sunset times or our work/school schedules, and can impact when you sleep or wake-up (and relatedly, when you are alert vs groggy).

Which brings us to chronotypes. Our chronotype is our “innate tendency to sleep at a particular time during a 24-hour period.” Chronotype is made up of the root “chron” from the Greek word “Khronos” means “time”.