It's not always easy to live at your own pace while being "socially correct." However, scientific studies reveal the importance of respecting our biorhythms and, more specifically, our chronotype.
Biorhythms are natural and regular cycles of physical, emotional, or mental changes. They influence our biology, metabolism, and sometimes even our mood (And yes, gentlemen, it's not our fault, it's because of our hormones).
Depending on their duration, they are classified into three types:
- Infradian rhythms, which last more than 24 hours, like the hormonal cycle.
- Ultradian rhythms, which last less than 24 hours, like the cardiac cycle.
- Circadian rhythms, which are 24-hour cycles like the sleep-wake cycle regulated by neurotransmitters.
The regulator of these biorhythms is an internal clock located in the suprachiasmatic nucleus of the brain. The suprachiasmatic nucleus receives information from over 20,000 neurons, including those from the retina, hence its high sensitivity to light, which plays a crucial role in the sleep-wake cycle. This internal clock is genetically regulated by about fifteen genes but is also influenced by environmental synchronizers like light, temperature, physical activity, and diet. By manipulating these synchronizers, we can adjust our sleep-wake cycle and chronotype in case of desynchronization.
How can desynchronization affect your health?
A chronotype desynchronization contributes to the development of pathological processes such as cancer, obesity and overweight, neurodegenerative and cardiovascular diseases, as well as premature aging. And guess what, the relationship is bidirectional: these pathologies can, in turn, disrupt circadian rhythms and chronotypes. So, you see the vicious cycle that develops; as they say in French: it's the dog chasing its tail.
The sleep-wake cycle mainly depends on two hormones:
- Melatonin: this is the one that makes you sleep like a koala.
- Cortisol: this is the one that wakes you up (among other functions) like a rooster.
Note that melatonin and cortisol have other roles, notably in inflammation and immunity, which is why they impact overall health.
To illustrate my point, I'll give you the example of people who work night shifts:
Understand your chronotype to better respect it
One reflection of this internal clock is the chronotype: the early riser, the perfect sleeper, the night owl. To define yours, think of weekend days without festivities or vacations aimed at rest and note:
- Natural bedtime: it's the moment when your eyes start to sting, and your eyelids become heavy.
- Natural wake-up time: natural awakening without noise or light.
You will normally notice that the times are similar each time. For example, for me, I know that from 10:00 PM, there's no point in talking to me; I'm asleep. And I naturally wake up between 7:30 and 8:00 AM (if Bingo, my cat, doesn't start telling me his life and walking on me... at 5:00 AM).
Thanks to this, you can now determine your chronotype:
- The early bird: your melatonin peak is around midnight. You are one of those who fall asleep at 9:00 PM on the couch and are up at 5:00 AM, full of energy. On vacation or not, your bedtime and wake-up times remain more or less the same... not easy to change your habits.
- The Mr or Miss perfect : melatonin peak at 2:00 AM, natural wake-up around 7:00 to 8:00 AM. You are one of those everyone envies!
- The night owl: your melatonin peak is at 4:00 AM. You are one of those who can party until the early hours and naturally wake up around 10:00-11:00 AM (even 12:00 PM). Your bedtime and wake-up times are very different during the week versus the weekend/vacations. You are much more effective in the evening than in the morning, but if you live with an early riser, it may cause a little problem 😅. Fortunately, this chronotype is a bit less "rigid" than the early riser, so it will be easier for you to shift your sleep/wake cycle.
How to reset your chronotype for the new school year
This section is more for night owls and some perfect sleepers who have obligations early in the morning
The first thing to do is to amplify and contrast the biorhythms using environmental synchronizers.
Expose yourself to light, especially in the early part of the day. In the evening, close the curtains between 6:00 and 7:00 PM and opt for a dim light atmosphere. Ideally, avoid turning on the TV and/or phone because the so-called "blue light" from screens strongly impacts melatonin secretion.
Regarding diet, my first advice is: eat during the day and not at night! So avoid that last square of chocolate before going to bed, supposedly "for comfort." If you really want to comfort yourself, cuddles, cardiac coherence, hypnosis, or why not a teddy bear are much more effective. The second advice is to have a light, plant-based meal with mainly vegetables. And finally, one last tip: eat at the same times every day, on weekdays, weekends, and during vacations.
Do your sport in the morning, EXCEPT if you are an early bird living with a night owl and you want to try to get closer to their rhythm (and vice versa). In these cases, evening physical activity can help.
Lower the temperature of your room at night.
Sleep neither too much nor too little and at the right time. Listen to your body; it tells you everything, so there's no need to fight against your drooping eyelids to watch the end of your favorite show—you might miss the sleep train and have to wait on the platform for 1.5 hours before the next sleep cycle. Try to sleep in a dark and quiet environment (a message to all those who snore: please buy earplugs for your partner or let them sleep in another room if possible 🙏).
Secondly, to shift your sleep/wake cycle earlier:
In the morning: no miracles, you will have to set your alarm earlier than your natural wake-up time every day at the same time. Invest in a light therapy lamp for 30 minutes every morning (it can be during your breakfast, for example, to avoid wasting too much time). Engage in physical activity—we've already talked about that—and finally, have a protein-rich breakfast (eggs, chicken, tofu, cheese, skyr).
In the evening: avoid light! I'm not saying to dine in the dark, but why not wear sunglasses if you can't dim the lights? Avoid stress; work emails or WhatsApp can wait until tomorrow... You may also consider taking melatonin supplements during the reset period, but that's with a trained therapist (like me) to know the right dose, form, and time.
Melatonin, Cortisol and biological tests
Be aware that excesses or deficits in cortisol and/or deficits in melatonin can also disrupt your chronotype. This can be caused by stress, dysbiosis, inflammation... Through a saliva test for cortisol levels (CAR) and a urine test for melatonin levels (6-sulfatoxymelatonin), deficits or excesses can be identified and thus lead to a more precise management.
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Sources:
Biological Rhythm and Chronotype: New Perspectives in Health. Angela Montaruli, Lucia Castelli, Antonino Mulè, Raffaele Scurati, Fabio Esposito, Letizia Galasso, Eliana Roveda. Biomolecules, 2021 Mar 24;11(4):487.
The relationship between chronotype and obesity: A systematic review. Seçil Ekiz Erim, Havva Sert. Chronobiol Int 2023 Apr;40(4):529-541.
Chronotype Differences in Body Composition, Dietary Intake and Eating Behavior Outcomes: A Scoping Systematic Review. Carlien van der Merwe, Mirjam Münch, Rozanne Kruger. Adv Nutr, 2022 Dec 22;13(6):2357-2405.
Shift Work, Chronotype, and Melatonin Rhythm in Nurses. Pedram Razavi, Elizabeth E Devore, Archna Bajaj, Steven W Lockley, Mariana G Figueiro, Vincent Ricchiuti, W James Gauderman, Susan E Hankinson, Walter C Willett, Eva S Schernhammer. Cancer Epidemiol Biomarkers Prev 2019 Jul;28(7):1177-1186.
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