Early riser, night owl or something else? Five Patterns May Define How We Sleep

For decades, many scientists thought that our sleep habits fell into two categories: we were either night owls or early risersthe latter group being considered healthier overall. However, new research shows there’s more to it than that. In a study published in Natural communications, researchers found five different sleep pattern subtypeseach with their own brain imaging patterns, behaviors and health outcomes.

These results could be useful for understanding how modern sleep habits affect our health, says sleep specialist Sonja Schütz. neurologist who studies sleep medicine at University of Michigan Health.

Researchers at McGill University trained a machine learning algorithm to analyze neuroimaging data, questionnaire responses and health reports from 27,000 UK Biobank participants. The algorithm looked at participants’ chronotypes, or typical patterns of sleep and wakefulness over 24-hour periods, and found brain imaging patterns corresponding to five distinct groups. These marked differences aroused the interest of the study’s lead author, neuroscientist Le Zhou: the participants “actually present different biological patterns visible in their brain images.”

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Three of the five subtypes were night owls of different flavors, and two were early birds, each with a bag of different properties. The first subtype of night owls, which Zhou refers to as “high-performance night owls,” were more likely to engage in risky behaviors and have difficulty with emotional regulation, but also higher cognitive performance. In contrast, the second subtype, which he calls “vulnerable night owls,” demonstrated more laid-back tendencies, with less physical activity and a greater risk of smoking. This subtype was associated with most health problems, including depression, heart disease, and diabetes, consistent with pre-existing ideas about the overall “night owl” group.

The last subtype, “male-dominated,” was more skewed toward men and was associated with higher cigarette and alcohol use, higher testosterone levels, and higher cannabis use than other subtypes. This specific subtype could help explain the frequency of the traditional night owl chronotype in males.

The “classic early riser” subtype, as Zhou puts it, matched traditional early riser characteristics, showing efficient brain networks, low rates of drinking and smoking, low risk taking and greater emotional stability. People in this group were the healthiest overall. However, the “female-dominated” subtype, which tended to be more reserved for women, was linked to higher rates of depression symptoms, lower testosterone levels, and more menstrual problems than the classic early bird subtype.

These chronotypes likely arise from complex interactions between people’s genetics, hormonal fluctuations, and environment, which include aspects such as their work schedules or exposure to light. But it’s not clear how all these factors cause a specific sleep pattern. Charlene Gamaldo, a neurologist at Johns Hopkins University School of Medicine who also specializes in sleep and was not involved in the study, notes that the research highlights how machine learning and large data sets can help advance our understanding of sleep chronotypes. She also points out that because the study relied on participants’ self-reported sleep information and associations rather than cause-and-effect relationships, further research is needed to determine whether chronotype itself explains the brain differences found or whether other factors may be responsible.

“We can’t tell from these data alone whether brain differences or health problems are causes or consequences,” adds Zhou. His team is currently comparing genetic data from people with different chronotypes to further explore these factors.