New research led by McGill University scientists suggests human sleep patterns (chronotypes) fall along a broader biological spectrum — with each subtype tied to unique health and behavioral traits — challenging the simple ‘early bird/night owl’ divide.
Zhou et al. identify a total of five distinct biological subtypes, each associated with different patterns of behavior and health. Image credit: Wok & Apix.
A chronotype is based on the parts of a 24-hour period when a person naturally feels most alert or ready to sleep.
Previous research has linked late chronotypes to worse health outcomes, but results have often been inconsistent.
“Rather than asking whether night owls are more at risk, the better question may be which night owls are more vulnerable, and why,” said Le Zhou, a Ph.D. student at McGill University.
Using AI, Zhou and colleagues combined brain imaging with questionnaires and medical records from more than 27,000 adults in the U.K. Biobank.
Their analysis revealed three types of night owls and two types of early birds.
One group of early birds had the fewest health problems overall, while the other was closely tied to depression.
As for night owls, one performed better than other groups in cognitive tests but had more emotional-regulation challenges.
Another group showed a tendency toward risk-taking behaviors and cardiovascular problems, while a third was more likely to have depression, smoke and face higher risks of heart disease.
“These subtypes are not defined only by bedtime or wake-up time,” said McGill University’s Dr. Danilo Bzdok.
“They reflect a complex interaction of genetic, environmental and lifestyle factors.”
Rather than ranking sleep types as better or worse, the researchers highlight how risks and strengths are distributed differently across the five profiles.
A more nuanced understanding of sleep profiles can help explain why the same sleep schedule can affect people differently, shifting research and sleep support away from one-size-fits-all approaches.
“In today’s digital and post-pandemic era, sleep patterns are more diverse than ever,” Zhou said.
“Understanding this biological diversity could eventually help inform more personalized approaches to sleep, work schedules and mental health support.”
The findings were published in December 22, 2025 in the journal Nature Communications.
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L. Zhou et al. 2025. Latent brain subtypes of chronotype reveal unique behavioral and health profiles across population cohorts. Nat Commun 16, 11550; doi: 10.1038/s41467-025-66784-8
