Are you an early bird or a night owl? Why scientists are moving beyond these groupings

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Are you a night owl who's always had trouble adjusting to an early bird schedule? Good news. Researchers are finding a more nuanced take on sleep patterns and how they affect health and behaviour.

Chronotypes refer to when a person naturally feels most inclined to sleep, wake up and perform physically and intellectually. Previous studies linked late-night chronotypes to worse health outcomes like heart disease and depression, but not consistently. 

A recent Canadian-led study of more than 27,000 U.K. adults published in Nature Communications is shedding light on who might benefit most from prioritizing sleep, physical activity or socializing — and when.

The study combined extensive brain imaging with computer science and questionnaires, cognitive tests and medical chart reviews.

The problem is that categorizing people into just two groups — late and early risers — is oversimplified, said Le Zhou, the study's lead author and a PhD student in neuroscience at McGill University.

"People always think the night owls tend to have bad health patterns and the early bird people tend to have healthier lifestyles," he said. "But our study found, actually, the short answer is not."

Instead of asking whether late sleepers face more health risks, Zhou wanted to find out which types were more vulnerable — and why. He and his co-authors found that among self-described night owls and early birds, there were five total subtypes, with each tied to a specific pattern of behaviour and health. 

Among night owls, there were:

Then, among early birds, there were:

While the study didn't quantify which group is most vulnerable, Zhou suggested that night owls get more physical activity and find healthier ways to manage anxiety instead of trying to change sleep timing. For the high-performance group, he said they should follow their natural rhythm to try and manage impulsivity and substance use.

In contrast, early risers experiencing issues might benefit from enhancing social support. 

Scientists suspect that these different chronotypes evolved so groups of early human ancestors could stagger their sleep times across the night to stay vigilant against night-time threats like predators. 

The study had people self-identify their chronotype with a questionnaire, something that University of Ottawa professor Rébecca Robillard noted as a drawback.