Five types of sleep and human internal clocks

The colloquial labels of night owl and early morning larklong used in sleep research, do not fully reflect the diversity of human internal clocks, a new study has found.

The research, led by McGill University (Canada) and published in the journal Nature Communicationshas proven that the two sleep-wake patterns, called chronotypes, contain a total of five subtypes different biological organisms, each associated with different patterns of behavior and health.

A chronotype is based on the parts of a period of 24 hours in which a person naturally feels more alert or ready to sleep. Previous research has linked late chronotypes to worse health outcomes, although results have often been inconsistent. The new findings help explain why, according to the authors.

“Rather than asking whether night owls are at greater risk, the better question may be which night owls are more vulnerable and why,” the lead author points out. Le Zhoua doctoral student in McGill’s Integrated Neuroscience Program.

A broader spectrum of AI sleep typesthe researchers combined brain imaging with questionnaires and medical records from more than 27,000 adults from the UK Biobank. The work was based on computational resources from the McConnell Brain Imaging Center and contributions from collaborators at the University of Montreal and the University of Oxford.

Their analysis revealed three types of night owls and two types of early risers. It was a group of early risers who had fewer health problems in general, while the other was closely linked with depression.

As for the night owls, one of them obtained better results than the other groups in the cognitive tests, but presented greater difficulties in emotional regulation. Another group showed a tendency towards risky behavior and cardiovascular problems, while a third were more likely to suffer from depression, smoking and a higher risk of heart disease.

“These subtypes are not defined solely by bedtime or wake-up time. They reflect a complex interplay of genetic, environmental, and lifestyle factors,” says lead author Danilo Bzdokassociate professor in the Department of Biomedical Engineering at McGill and holder of the CIFAR Canada Chair in Artificial Intelligence at Mila.

Instead of classifying types of sleep 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 may help explain why the same sleep schedule can affect people differently, moving sleep research and support away from one-size-fits-all approaches.

“In today’s digital and post-pandemic era, sleep patterns are more diverse than ever,” he said. Zhou. “Understanding this biological diversity could, over time, help define more personalized approaches to sleep, work schedules, and mental health support.”

The team is now turning to genetic data to determine if chronotype subtypes have biological roots from birth.