Saying to yourself “I’m more of an evening person” or “clearly a morning person” seems so natural that we forget everything that’s going on behind these labels. However, a vast international study has just shaken up this well-established duo, showing that our internal clock comes in much more subtle profiles.
Published in the journal Nature Communicationsthis research conducted by McGill University combined brain imaging, medical records and questionnaires from more than 27,000 British adults. Result: instead of two categories, scientists distinguish five subtypes of chronotypeassociated with very different behaviors and health risks. It remains to be understood what profile each one resembles.
From “sleeping late” to “rising early”: what the chronotype really says
The chronotype corresponds to the times of the day when we spontaneously feel most awake or most sleepy. Studies already linked late chronotypes to more health problems, but the results often contradicted each other. “Rather than asking whether late sleepers are more at risk, the better question is which late sleepers are most vulnerable, and why.“, explained Le Zhou, quoted by McGill University.
To refine this picture, the team used artificial intelligence algorithms applied to three types of brain MRI scans and hundreds of lifestyle, diagnostic and medication variables. The same profiles were then looked for in 10,550 American adolescents from the ABCD study, showing that these differences already appear very early.
Five biological profiles, three in the evening and two in the morning
The researchers describe three subtypes of “late to bed” and two of “early to rise”. “These subtypes are not defined solely by bedtime or wake-up time. They reflect a complex interaction of genetic, environmental and lifestyle factors“, emphasized Danilo Bzdok, co-lead author.
In summary:
- A late night sleeper with a high-performance brainwith better scores on cognitive tests, but more difficulty regulating emotions, risky behaviors and consumption of alcohol, tobacco or cannabis, with lower vitamin D levels;
- A high-risk late nightmarked by smoking, little physical activity, waking up late, more depression, hypertension, diabetes, cardiovascular and respiratory diseases, and frequent use of cardio and antidiabetic medications;
- A generally “preserved” early riser : get up earlier, non-smoker, rare alcohol, little risk-taking, without clear over-representation of pathologies or treatments;
- An early riser especially femaleassociated with menstrual disorders, lower testosterone levels, higher SHBG protein, depressive symptoms and the use of antidepressants and analgesics;
- A late night, especially malelinked to baldness, higher testosterone, prostate diseases, hypertension, cardiovascular medications, high consumption of alcohol, tobacco and cannabis and a high propensity for risk-taking.
Towards truly personalized sleep advice
These profiles prove that there is not a “good” or “bad” type of sleeper, but combinations of cognitive strengths, cardiovascular or psychological vulnerabilities, and hormonal influences. The same work schedule could help a “robust” early riser and weaken a late sleeper already exposed to depression or hypertension. “Today, with digital technology and the post-pandemic, sleep habits are more diverse than ever“, Le Zhou observed. “Understanding this biological diversity could ultimately help provide more personalized approaches to sleep, work schedules and mental health support“.
The team is now analyzing genetic data to find out if these five profiles are anchored from birth or are mainly sculpted by the environment.