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

ar you a nighttime bird of minerva who's ever had bother 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.

"The chronotypes were actually determined based on a fairly simple question," said Robillard, who wasn't involved with the study.

The findings would be more robust with multiple biological measures like hormonal or temperature changes, she said, which she believes the researchers will do soon. 

Still, Dr. Michael Mak of the Centre for Addiction and Mental Health in Toronto noted that a strength of the study was that investigators validated the findings against another database of younger people in the U.S. This increases scientists' confidence in their findings and conclusions.

"You're looking at large, broad strokes" from thousands of people, said Mak, who also wasn't involved with the study. "Individual differences are probably much bigger."

Even if you don't know your exact chronotype, there's still an easy hack, said Jessica Chalekas, an expert in the sociocultural anthropology of sleep at Brunel University in London, England, who was independent of the study. 

"Take a week or a couple of weeks to really check in with yourself and notice your own patterns," Chalekas said. "When do I feel like I'm functioning my best?"

What could this all mean for understanding of chronotypes? Robillard called the study impressive at pushing the bar on associations between chronotypes and brain patterns.

As director of a clinical sleep research unit, Robillard suggested that people adapt their daily schedule to facilitate "enabling your chronotype to thrive in your daily routine."

For later risers, that could include light exposure to push the internal rhythm to a slightly earlier phase.  

"The sun is really a strong ally here," she said. That's why she recommends taking a morning coffee break outside, even when it's relatively cloudy. 

As much of Canada approaches the spring clock change, Robillard noted that late risers are more affected by time change. It's one of the reasons she advocates abolishing daylight saving time.

Recent models suggest that the consistency of one's sleep schedule also matters, she said. That means yo-yoing between waking up early during the week and sleeping in on weekends isn't ideal, because it sends conflicting signals to the body's internal clock, which struggles to keep track, she said.

Of course, there are limits to trying to change one's chronotype, said Mak, a sleep medicine specialist.

"The changes are not going to be permanent and they probably won't obviate the health risks," he said.

In the world of sleep medicine, there's a lot of research on managing body clock rhythms, said Dr. Maha Alattar, an associate professor of neurology at Virginia Commonwealth University and a sleep specialist. She counters societal misperceptions of people with late chronotypes. 

"One of the things that I do with a lot of those patients, when I figure out that's what they have, is to reassure them that you're not lazy," Alattar said.

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"You just have this circadian rhythm that's not in line with the world schedule. And there's nothing wrong with you, but it is your obligation to make sure that you have good habits in the evening and in the morning."

Alattar also pointed to how chronotypes can become dysfunctional in individuals in nursing homes or with dementia. The brain cells that generate the ability to form body clocks or circadian rhythms no longer respond to stimulus from the sun. 

At the end of the day, we all need to rest. Respect your biology for sleep and wakefulness, Alattar said.

"A good night's sleep is an investment in your health."

Journalist

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