Scientists Discover Five Types of Night Owls and Early Birds. Which Type Are You?

Forget everything you’ve been told about being a simple "morning person" or a "night owl."

Researchers have long divided humanity into two simple camps: the early risers and the late sleepers. You were either a morning lover or a morning hater. But according to a groundbreaking study of over 27,000 participants, that binary is dead.

Instead, researchers have uncovered five distinct latent brain subtypes of chronotypes. Each chronotype (an individual’s natural, genetically determined propensity to sleep, wake, and perform at certain times of the day) carries its own unique cocktail of health risks and cognitive rewards.

“Rather than asking whether night owls are more at risk, the better question may be which night owls are more vulnerable, and why,” said lead author Le Zhou, a PhD student in McGill’s Integrated Program in Neuroscience.

The Truth Is Much More Personal

To map these hidden biological profiles, the researchers harnessed two of the largest and most comprehensive biomedical resources in the world: the UK Biobank and the ABCD Study. You can’t just trust people to self-report how they sleep, you have to look at the data.

The UK data, in particular, was extremely useful. The data included a massive library of three-dimensional brain scans. The researchers focused on gray matter volume, the integrity of white matter “wiring,” and functional connectivity. To make sense of this mountain of data, they deployed an AI method called Partial Least Squares (PLS) regression.

Unlike a standard survey, this algorithm analyzed brain architecture and behavioral “fingerprints” simultaneously. It looked for the “latent” structures — the places where your brain’s physical build and your sleep habits actually overlap. The results showed three different ways to be a night owl and two ways to be an early bird.

“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, Associate Professor in McGill’s Department of Biomedical Engineering and Canada CIFAR Artificial Intelligence Chair at Mila.

The Five Types

The researchers describe the following types of sleepers:

• The High-Performing Night Owl. This is the “classic” evening type, late waker, but with a cognitive edge. While they often struggle with emotional regulation (and often report feeling “fed up” or irritable), they are cognitively sharp. They show faster reaction times and better performance in puzzle-solving tasks. Their brains show increased gray matter in the limbic system and stronger wiring in attention networks.
• The Vulnerable Owl. This group reveals a darker side of late nights. This subtype is strongly linked to depression, smoking, and cardiovascular risks like high blood pressure and diabetes. Unlike the first group, their defining feature is a widespread reduction in the integrity of their brain’s white matter “wiring”.
• The Healthy Early Bird. This is the classic standard of positive morning lovers. These individuals get up early, smoke less, drink less, and have almost no major health issues reported in their medical records. They are often more educated and take fewer risks.
• The Female-Biased Morning Type. This subtype is predominantly seen in women. While they are early risers, they are also more prone to depressive symptoms and menstruation disorders. Biologically, this is linked to lower testosterone and higher sex hormone-binding globulin (SHBG).
• The Male-Biased Night Owl. This is a distinctly male-heavy evening group. They are risk-takers who consume more alcohol and cigarettes and face higher risks of prostate issues and hypertension. Their profile is marked by higher testosterone levels.

To validate these findings, the team looked at 10,550 US children from the ABCD Study. They found the same biological patterns in youth, but they can change as people age.

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Why Does This Matter?

There is an evolutionary logic to this variety. In the early days of human history, a tribe where everyone slept at the same time was a tribe waiting to be eaten. We needed “sentinels” active at different hours.

But what do we do with this information?

The main idea is that we can customize interventions and personalize medicine for these subtypes. Instead of a “one size fits all” approach, we can now customize interventions. For instance, a “Vulnerable Owl” struggling with depression might respond best to bright light therapy to reset their clock, while a “Female-Biased Morning Type” might require interventions focused on hormonal balance and social support.

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Ultimately, the study shows why the “one size fits all” approach to health and productivity is failing and gives clues as to how we can do better.

The study was published in Nature Communications.