Beyond Early Birds & Night Owls: 5 Chronotypes Revealed

New Study Uncovers Five Distinct Sleep-Wake Patterns

For decades, sleep science has operated on a simple binary: you're either an early bird or a night owl. But groundbreaking research from McGill University published in Nature Communications reveals this classification is far too simplistic. Using artificial intelligence to analyze brain scans, questionnaires, and medical records from over 27,000 UK Biobank participants, researchers have identified five distinct chronotypes - three types of night owls and two types of early birds, each with unique health and behavioral profiles.

The Complex Reality of Our Biological Clocks

A chronotype represents your natural preference for sleep and wake times within a 24-hour cycle. While previous studies often suggested morning people were healthier and lived longer, the new research explains why those findings were inconsistent. 'Instead of asking whether night owls are at greater risk, a better question is which night owls are more vulnerable and why,' explains lead author Le Zhou, a PhD candidate at McGill University, in an interview with Medical Xpress.

The study's sophisticated AI analysis combined three different brain imaging modalities with nearly 1,000 behavioral and health measures. 'These subtypes are not just determined by when people go to sleep or wake up. They reflect a complex interplay of genetic, environmental, and lifestyle factors,' says researcher Danilo Bzdok of McGill.

The Five Chronotypes Explained

Morning Type 1: This group generally has the fewest health problems, with minimal substance use and low-risk behaviors. They represent the classic 'healthy early bird' profile.

Morning Type 2: More common in women, this subtype shows strong associations with depressive symptoms, hormonal characteristics like low testosterone, and use of antidepressants.

Evening Type 1: These night owls perform better on cognitive tests but struggle with emotional regulation. They show more risk-taking behaviors and lifestyle factors like alcohol and cannabis use.

Evening Type 2: Strongly linked to depression, smoking, and increased cardiovascular risks including hypertension and diabetes. This group uses more antidepressants and cardiovascular medications.

Evening Type 3: More common in men, this subtype shows elevated cardiovascular risks, higher alcohol and cigarette consumption, and associations with prostate-related conditions.

Implications for Personalized Health

The research moves beyond ranking sleep types as 'better' or 'worse' and instead emphasizes how risks and strengths are differently distributed across the five profiles. This nuanced understanding could explain why the same sleep schedule affects people differently and why blanket sleep advice often fails.

'In the digital and post-pandemic era, sleep patterns are more diverse than ever,' Zhou notes. 'Understanding this biological diversity can ultimately contribute to more personalized approaches to sleep, work schedules, and mental health support.'

The team is now focusing on genetic data to determine whether chronotypes have a biological basis from birth. This research could lead to more targeted interventions for those at higher risk of depression, cardiovascular disease, or cognitive challenges based on their specific chronotype profile.

The study validates in 10,550 US children from the ABCD Study cohort that these chronotype differences begin emerging early in life, suggesting these patterns aren't just lifestyle choices but have deeper biological roots.