Scientists Discovered There Are Actually 5 Sleep Chronotypes, Not 2 — Here's What Each Means for Your Health

For years, you've probably slotted yourself into one of two camps: early bird or night owl. Maybe you've even taken one of those online quizzes that asks whether you'd naturally wake at 5 a.m. or drag yourself out of bed at 9. Turns out, that's a bit of an oversimplification. Researchers at McGill University have just published findings suggesting there aren't two sleep chronotypes, but five distinct ones, each with its own set of health associations [1].

The study, published in Nature Communications, used artificial intelligence to comb through brain imaging data, questionnaires, and medical records from more than 27,000 adults in the UK Biobank [2]. What emerged was a more nuanced map of how people's biological clocks vary, and it might explain why some of the health advice you've read about sleep never quite seemed to fit your experience.

Why Two Categories Never Made Sense

If you've ever felt judged for being a night owl, or misunderstood your own body's preferences, you're not imagining it. Previous research linking late chronotypes to worse health outcomes has been inconsistent, and this new work helps explain why [2]. Lumping all night owls together misses the fact that some are doing just fine, thank you very much, while others are genuinely struggling.

The McGill team, led by Le Zhou, a PhD student in McGill's Integrated Program in Neuroscience, trained their AI model to find patterns across brain structure, lifestyle factors, and medical histories. The algorithm didn't know in advance how many groups it should find. It just looked for people who were biologically similar in how their sleep-wake cycles behaved [2].

What came back was five clusters. Two fell under what we'd traditionally call early birds, and three under night owls [1]. The subtypes weren't just about what time you prefer to wake up. They were tied to measurable differences in brain wiring, mental health profiles, and even cardiovascular risk.

The Two Morning Lark Subtypes

The first morning lark type the researchers identified showed the fewest health problems of any group. These were people who tended to be non-smokers, drank alcohol rarely, didn't take many risks, and reported fewer emotional issues [3]. If you picture the stereotype of the serene early riser who jogs before breakfast and has never heard of insomnia, this is close to that. But here's the thing: this group also reported higher anxiety levels [3]. So even the "healthiest" chronotype isn't without its complications.

The second morning lark type skewed more female and showed a different pattern. These individuals had higher rates of depressive symptoms, were more likely to be on antidepressant medications, and showed higher rates of menstruation disorders [3]. The researchers noted this group might be particularly vulnerable to the pressure of a world designed for early risers, and may benefit from checking in with a doctor if they notice mood changes that persist.

The Three Night Owl Subtypes

Here's where things get more complicated, because the three night owl groups didn't share much in common beyond preferring later sleep times.

The first night owl group showed what the researchers called risky lifestyle behaviours and emotional regulation difficulties, but here's the interesting part: they also performed better on cognitive tests and had faster reaction times [3]. If you've ever felt like you do your best thinking late at night and wondered if that was just rationalizing your bad habits, this data suggests you might genuinely be onto something. The trade-off appeared to be in emotional regulation, so if you recognize yourself in this description, building in some stress-management practices might be particularly valuable.

The second night owl group presented a more concerning picture. These individuals had higher rates of depression, were more likely to smoke, showed higher cardiovascular risk, and had lower physical activity levels [3]. Their brains also showed decreased white matter integrity, which is associated with slower communication between brain regions [3]. This group was more likely to be taking antidepressant medication [3]. If you fit this profile, it is worth taking the mental health and cardiovascular risk associations seriously, not as a judgment, but as information.

The third and final night owl subtype was more male-dominated than the others. This group showed a mix of risk-taking behaviours and cardiovascular problems, as well as notably higher rates of prostate-related health concerns [3]. They also had higher testosterone levels and were more likely to use alcohol, cigarettes, and cannabis [3]. High blood pressure was also more prevalent in this group [3].

What This Means for You

The researchers validated their findings by applying the same model to a separate group of more than 10,000 US teenagers and finding similar subtype patterns [3]. That cross-cohort consistency is what gives the findings real weight, and it suggests these aren't just artefacts of the UK Biobank sample.

Rather than asking whether night owls are more at risk, the senior author Danilo Bzdok said the better question may be which night owls are more vulnerable, and why [2]. That reframing matters for how we think about health advice. Blanket recommendations about sleep schedules may work well for some people and miss the mark entirely for others.

"In today's digital and post-pandemic era, sleep patterns are more diverse than ever," Zhou noted [1]. "Understanding this biological diversity could eventually help inform more personalized approaches to sleep, work schedules, and mental health support."

A More Honest Take on Sleep

There is something quietly validating in seeing the two-category model fail. It means the frustration you've felt trying to fit your own sleep patterns into someone else's framework was warranted. Your experience of being a night owl who can't seem to get things done before noon, or an early bird who mysteriously crashes hard after 2 p.m., reflects something real about your biology, not just a discipline problem to be solved with better bedtime habits.

That said, if you recognised yourself in the higher-risk subtypes, that recognition is useful information, not a reason to despair. Some of the associations, like cardiovascular risk, are exactly the kinds of things that respond well to targeted interventions when you know what you're working with. Talking to a doctor about your specific profile, rather than relying on generic sleep hygiene advice, may be the honest path forward.

These findings also complicate the narrative around chronotypes and productivity. The idea that night owls are less disciplined or less capable is a cultural story that doesn't survive contact with this kind of data. One of the night owl subtypes showed superior cognitive performance [3]. Another struggled in ways that had little to do with willpower. The diversity here is the point.

The team is now looking at genetic data to determine whether these chronotype subtypes have biological roots from birth [1]. That future work may eventually allow someone to know their subtype from a simple test, long before the habits and health problems compound. Until then, this research is a reminder that the sleep you need is not the sleep someone else prescribes.