Study Reveals Diversity in Human Sleep Types

The familiar categories of “night owl” and “early bird” fail to encompass the full range of human sleep patterns, according to a new study led by McGill University and published in Nature Communications. The research shows that common chronotypes, which describe when people naturally feel most alert or sleepy in a 24-hour cycle, can be divided into five distinct biological subtypes. Each subtype is linked to unique behavior patterns and health outcomes.

Chronotypes have long been associated with different risks to health, with individuals who stay up later often reported to experience poorer outcomes. However, these findings have not always been consistent. The new study offers an explanation for this variation. As lead author Le Zhou noted, “Rather than asking whether night owls are more at risk, the better question may be which night owls are more vulnerable, and why.”

To uncover these subtypes, the researchers used artificial intelligence to analyze brain imaging data, medical records, and questionnaire results from over 27,000 adults in the U.K. Biobank.

The analysis identified three types of night owls and two types of early birds. Among early birds, one group showed the fewest health challenges, while the other was linked to depression. The night owl subtypes displayed more complex patterns. One performed well on cognitive tasks but struggled with emotional regulation. Another showed a higher likelihood of risk-taking behavior and cardiovascular problems. A third was more likely to smoke, experience depression, and face increased risk of heart disease.

“These subtypes are not defined only by bedtime or wake-up time. They reflect a complex interaction of genetic, environmental and lifestyle factors,” said senior author Danilo Bzdok. The researchers emphasized that no sleep profile is inherently better or worse; rather, each involves different strengths and vulnerabilities.

The study suggests a shift toward more personalized sleep and health approaches. As Zhou explained, “In today’s digital and post-pandemic era, sleep patterns are more diverse than ever. Understanding this biological diversity could eventually help inform more personalized approaches to sleep, work schedules and mental health support.”