Early Bird or Night Owl? Study Finds It Might Not Be So Simple
Key Findings
A landmark 2025 study has dismantled the binary "night owl vs. early bird" model, using machine learning to identify five distinct neurobiological subtypes of chronotype. By analyzing brain imaging from over 27,000 people, researchers revealed that sleep preference alone doesn't dictate health; instead, specific brain profiles determine whether a sleep pattern is "healthy" or "risky." The study identified high-functioning night owls with superior cognitive speed, distinct from a separate evening group linked to depression, while also uncovering a female-biased "early bird" group prone to anxiety, proving that waking up early isn't always protective.
For decades, the field of sleep medicine has operated under a relatively binary paradigm regarding chronotype: the "early bird" (morningness) and the "night owl" (eveningness).
This dichotomy has served as a foundational heuristic for understanding patient behavior, risk profiles, and recovery strategies. The prevailing consensus has historically favored morningness as the phenotype of health, while eveningness has been broadly associated with psychiatric, metabolic, and cardiovascular morbidity.
But hasn’t that bias, prevalent in both the medical field and popular culture, always felt a little too simplistic? Is being a night owl genuinely bad? And do early birds always catch the worm?
A landmark 2025 study published in Nature Communications provides the neurobiological evidence to challenge these broad perceptions.
By leveraging machine learning to analyze multimodal brain imaging and behavioral data, researchers have deconstructed the monolithic "morning vs. evening" model, revealing five distinct biological subtypes that demand a re-evaluation of how we assess and treat circadian rhythmicity.
Part I: The Study - Breaking the Paradigm
The study, titled "Latent brain subtypes of chronotype reveal unique behavioral and health profiles across population cohorts," was led by Le Zhou, Danilo Bzdok, and colleagues at McGill University.
The research team sought to overcome the limitations of traditional self-report chronotype assessments, which treat morningness and eveningness as single, continuous variables.
Methodology: The investigators utilized a massive dataset from the UK Biobank, comprising 27,030 individuals. Unlike previous studies that correlated single variables, this research employed a supervised pattern-learning framework (Partial Least Squares, or PLS) to integrate three complementary brain-imaging modalities:
Grey Matter Volume (GMV): Assessing structural density.
White Matter Integrity: Measuring the microstructural health of neural tracts.
Resting-State Functional Connectivity: Evaluating communication between brain regions.
These neurobiological features were mapped against "deep" behavioral phenotyping, including medical diagnoses, lifestyle factors, and prescription records.
To ensure the robustness of their findings, the team validated the identified subtypes in an independent cohort of 10,550 children from the Adolescent Brain Cognitive Development (ABCD) Study.
This cross-cohort validation suggests that these neurobiological profiles may be trait-like features that emerge early in life, rather than transient states developed solely in adulthood.
Potential Data Limitations
While this study represents a significant leap forward in circadian neurobiology, experts must interpret the findings within the context of specific limitations:
Cross-Sectional Design: The primary analysis relies on observational data. While the identification of subtypes is robust, the study cannot definitively establish causality. It remains unclear whether brain structure drives the chronotype behaviors or if chronic circadian misalignment remodels brain structure over time.
Self-Reported Chronotype: Despite the sophisticated neuroimaging, the "ground truth" for chronotype was initially based on self-reported preference. Although the researchers validated this with accelerometer (actigraphy) data, the subjective nature of the primary label introduces potential bias.
Cohort Specificity: The UK Biobank population is predominantly of European descent and tends to be healthier and wealthier than the general population ("healthy volunteer bias"). While the ABCD validation helps, generalizability to diverse global populations remains an area for future investigation.
Reverse Causality: In subtypes associated with depression or poor health, it is difficult to disentangle whether the chronotype subtype predisposes the individual to disease or if the disease state alters the circadian phenotype.
Part II: Findings - 5 Sleep Subtypes
The core discovery of the study is that "morningness" and "eveningness" are not monolithic. Instead, the researchers identified five latent subtypes, three associated with eveningness and two with morningness, each characterized by distinct neurobiological architectures and health risks.
Crucially, the brain regions most heavily implicated across these subtypes were not the primary visual or motor cortices, but rather the basal ganglia, limbic system, hippocampus, and cerebellum.
This points to a fundamental link between our sleep-wake rhythms and the neural circuits governing habit formation, emotional regulation, and reward processing.
Subtype 1: a night owl pattern associated with emotional regulation and cognitive performance
Often defying the "lazy" stereotype, these individuals represent the functional side of eveningness.
Their brains are wired for high performance, typically showing faster reaction times and superior problem-solving skills compared to other groups.
The primary downside for this group is not cognitive but emotional; while they may be brilliant at 11 PM, they frequently struggle with mood regulation and irritability.
For these people, forcing an early morning schedule might actually blunt their cognitive edge, suggesting they should prioritize emotional management rather than fighting their natural clock.
Subtype 2: a night owl pattern linked to depression, smoking and cardiovascular risks
Conversely, this group embodies the negative health statistics historically linked to night owls.
Staying up late is less of a functional preference for them and more of a biological misalignment, as their brain scans reveal reduced connectivity in areas governing mood and movement.
Unlike their high-functioning counterparts, they receive no cognitive boost from the night and face a strong predisposition toward depression, anxiety, and unhealthy habits like smoking.
Eveningness here is a vulnerability rather than a superpower, making strict sleep hygiene and professional mental health support essential.
Subtype 3: a morningness pattern with less substance use and fewer health issues
Long considered the gold standard of sleep health, this group generally lives up to the hype.
Their brain connectivity supports high resilience and consistent energy, allowing them to report the highest life satisfaction and lowest rates of substance abuse.
There is virtually no hidden trade-off for these individuals; their natural rhythm aligns perfectly with societal norms and promotes excellent physical health. If you fit this profile, your current habits are likely serving you well and require no modification.
4. The Anxious Early Bird Female-Biased Morningness Pattern
Perhaps the most surprising finding of the study is that waking up early is not guaranteed to be healthy.
More common in women, the Anxious Early Bird rises early not because they are well-rested, but often due to fragmented sleep or anxiety.
Despite their "healthy" wake-up time, they suffer from high rates of depression similar to the Struggling Night Owl.
It is a critical distinction for anyone who wakes at 5 AM feeling wired or worried rather than refreshed, as this may signal insomnia or mood disorders rather than a robust circadian rhythm.
5. The Physical Night Owl Male-Biased Eveningness
Distinct from the psychiatric risks seen in other groups, this profile is predominantly found in men and carries consequences that are almost entirely physical.
Their neural patterns differ significantly from the other evening types, showing strong links to the body’s autonomic systems that control heart rate and metabolism.
While they may not struggle with depression, they face elevated risks for heart issues, high blood pressure, and diabetes, often accompanied by a tendency toward risk-taking behavior.
Men with this sleep pattern should prioritize cardiovascular monitoring, as their late nights may be placing silent stress on their heart.
Part III: Implications - More Nuance is Needed
The identification of these five subtypes has immediate and profound implications for experts in sleep, performance, and recovery.
1. Refiming "Social Jetlag" Interventions
The standard prescription for night owls has been to force a shift toward morningness to reduce "social jetlag."
However, for Subtype 1, this may be counterproductive. These individuals possess a resilient neurobiological substrate for evening activity. Forcing them into an early schedule might degrade their natural cognitive advantage.
Conversely, for Subtype 2, aggressive circadian entrainment (light therapy, melatonin) might be a critical psychiatric intervention, not just a lifestyle tweak.
2. Differential Diagnosis in Depression
When a patient presents with depression and sleep disturbance, the chronotype matters.
An early-rising patient (potentially Subtype 4) requires a different investigative lens than a late-sleeping patient. For Subtype 4, early waking is likely a symptom of the mood disorder (terminal insomnia) rather than a healthy trait.
For Subtype 2, the eveningness and depression could be co-morbidities rooted in shared white matter deficits.
3. Targeted Cardiovascular Screening
Sleep experts often focus on apnea when assessing cardiovascular risk.
This study suggests that Subtype 5 (Male-Biased Eveningness) warrants proactive cardiovascular monitoring solely based on their circadian phenotype, even in the absence of obvious sleep disordered breathing. Their risk profile is intrinsic to their neuro-metabolic architecture.
4. Occupational Health and Shift Work
Workplace wellness programs often treat all shift workers the same. This data suggests that Subtype 1 individuals are the ideal candidates for night shifts or flexible late schedules, as they maintain cognitive acuity and white matter health.
Placing Subtype 2 or Subtype 5 individuals in night shift roles could be much more dangerous, accelerating their pre-existing vulnerabilities to depression and cardiovascular disease.
Early Bird or Night Owl? Take the Quiz
Instructions: Answer the following questions honestly to find which neurobiological profile matches your sleep habits best.
Step 1: The Time Check If you were entirely free of work or family obligations, when would you naturally prefer to sleep and wake?
A. I prefer to bed down around 9:00 PM or 10:00 PM and wake up with the sun. (Go to Step 2)
B. I prefer to stay awake until midnight or later and sleep late into the morning. (Go to Step 3)
Step 2: The Morning Split (For the Early Risers) You identified as a Morning Person. Which of these statements describes your mental state best?
Option A: "I wake up feeling genuinely refreshed and optimistic. I rarely struggle with mood swings or anxiety, and I generally feel satisfied with my life."
Your Result: Early Bird Subtype 3
What this means: You are the standard for healthy sleep. Your natural rhythm is protecting your physical and mental health. Keep doing exactly what you are doing.
Option B: "I wake up early, but often because I am worried or anxious. I frequently feel tired despite my early hours, and I struggle with feelings of depression or high stress."
Your Result: Early Bird Subtype 4
What this means: Your early rising might be a symptom of "terminal insomnia" or anxiety rather than a healthy preference. You may need to focus on stress reduction or speak to a specialist about sleep fragmentation.
Step 3: The Evening Split (For the Night Owls) You identified as a Night Owl. Which of these statements describes your experience best?
Option C: "My brain 'turns on' at night. I am sharp, creative, and productive after 10 PM. However, I often feel irritable or have trouble controlling my temper."
Your Result: Night Owl Subtype 1
What this means: You are a functional night owl. Do not try to force yourself into a 5 AM club routine, as you will likely lose your cognitive edge. Focus on managing your mood, not changing your bedtime.
Option D: "I stay up late, but I don't feel productive. I often feel low, unmotivated, or depressed. I might smoke or skip exercise, and I generally feel like my sleep schedule is dragging me down."
Your Result: Night Owl Subtype 2
What this means: Your evening preference is likely linked to a broader health vulnerability. For you, sticking to a stricter routine and seeking support for mood health is crucial.
Option E: "I am a male who enjoys staying up late. I don't feel depressed, but I do have concerns about my blood pressure, heart health, or weight. I also tend to enjoy high-adrenaline or risky activities."
Your Result: Night Owl Subtype 5
What this means: Your late nights are a physical risk factor. Even if you feel mentally fine, your body may be under stress. Prioritize heart health screenings and cardiovascular fitness.
Final Thoughts: The Five Types of Sleeper
The Zhou et al. study signals the end of the "one-size-fits-all" era in circadian medicine. We can no longer broadly categorize eveningness as "bad" and morningness as "good."
The reality is that a "night owl" may be a cognitively superior executive with a specific emotional vulnerability, or a patient at severe risk of metabolic syndrome. Similarly, an "early bird" may be a model of resilience or a patient masking significant depressive pathology.
For the sleep and recovery expert, this means our assessment protocols must evolve. We must look beyond the clock time of sleep onset and wakefulness to understand the phenotypic context of that timing.
Future tools may allow us to identify these subtypes clinically, enabling us to prescribe precision recovery protocols that align not just with a patient's schedule, but with their specific neurobiological architecture.
Article FAQ
How to know if you are a night owl or an early bird?
The most accurate test is to observe your natural sleep pattern on "free days" when you have no work or family obligations. If you naturally fall asleep after midnight and wake up late, you are a night owl (eveningness). If you prefer sleeping by 10 PM and rising with the sun, you are an early bird (morningness). However, new research suggests you should also monitor your mood: if you wake early but feel anxious, or stay up late but feel mentally sharp, this helps identify your specific biological subtype.
Is it better to be a night owl or an early bird?
Traditionally, society views being an early bird as "better" for health, but a 2025 study reveals this is not always true. While "Classic Early Birds" often have excellent health, some night owls ("Sharp Night Owls") actually possess superior cognitive speed and brain connectivity. Conversely, some early risers suffer from high rates of depression. Ultimately, it is better to be in a pattern that aligns with your natural biology rather than forcing a schedule that causes social jetlag.
What is a chronotype?
A chronotype is your body's natural inclination to sleep and wake at specific times, driven by your internal circadian rhythm. It determines whether you feel most alert in the morning ("early bird") or the evening ("night owl"). Beyond just sleep preferences, your chronotype influences your hormone release, body temperature, appetite, and peak cognitive performance throughout the day.
Can a night owl become an early bird?
While you can force a change in your wake-up times using alarms and light exposure, you may not be able to change your underlying neurobiology. For "Sharp Night Owls," forcing an early schedule might actually degrade cognitive performance and white matter health. It is often more effective to adjust your lifestyle to fit your chronotype rather than fighting your biology, unless your current schedule is causing severe social or health issues.
Why do I wake up early but still feel tired and anxious?
You may fit the "Female-Biased Morningness" profile identified in recent studies. This group wakes up early not because they are well-rested, but often due to fragmented sleep or anxiety. Unlike "Classic Early Birds," this group has a higher risk of depressive symptoms. If you wake early but feel unrefreshed or worried, this is likely a symptom of a sleep or mood disorder rather than a healthy circadian preference.
What are the health risks of being a night owl?
The health risks depend entirely on your subtype. One group of night owls (often male) faces higher risks for cardiovascular issues, hypertension, and metabolic strain. Another group (often linked to depression) faces higher risks of mental health struggles and nicotine use. However, a third group of night owls is metabolically and mentally healthy. Understanding which type you are is necessary to know your specific risks.
