The scans are in: poorer sleep habits, including night-owl patterns, make your brain look older than your birthday says it should.
If you’re a proud night owl, brace yourself.
A large brain-imaging study just landed with a clear signal: people with poorer sleep profiles show brains that look older than their calendar age—and chronotype (morning vs. evening type) is one of the factors rolled into that risk.
The work is new (published the week of October 1–2, 2025), it’s MRI-based, and it connects the dots between sleep habits, inflammation, and “brain age.”
What the MRI study actually found
Researchers at Sweden’s Karolinska Institutet analyzed brain scans from 27,500 middle-aged and older adults in the UK Biobank.
Using machine-learning models trained on hundreds of MRI features, they estimated each participant’s “brain age” and compared it to their real age.
People with poorer overall sleep scored older—on average by about a year for those in the lowest sleep-health tier. In statistical terms, every one-point drop on a five-factor sleep score corresponded to roughly six months of extra “brain age.”
Here’s the part relevant to night owls: chronotype (being a morning or evening person) was one of the five sleep factors considered, alongside sleep duration, insomnia, snoring, and daytime sleepiness.
A less healthy pattern across these dimensions—night-owl tendencies often pair with short sleep on workdays—tracked with an older-looking brain.
Why night owls should care
You can be an evening type and still sleep well, but many of us don’t. Social schedules tilt early: morning commutes, 8 a.m. classes, kids who wake at dawn.
If your body wants to fall asleep at 1 a.m. yet your alarm screams at 6, that chronic “social jet lag” can push you into the poor-sleep bucket. That’s exactly where the MRI signal gets louder.
Poor sleepers’ brains, on average, appeared one year older than their chronological age—a small number in a single year, but meaningful across decades of compounding risk.
This result lines up with separate 2025 cohort work showing evening types may face faster cognitive decline over time, in part through behaviors that tend to cluster at night—fragmented sleep, more smoking, or extra late-night screen time.
None of this proves causation, but the direction of the evidence is getting consistent.
How the researchers measured “brain age”
“Brain age” isn’t a vibe; it’s a computed metric that compares your MRI features to typical patterns across ages.
In this study, the team fed more than a thousand MRI phenotypes into a model that outputs a predicted biological brain age.
The difference between that prediction and your actual age is called the “brain age gap.” Bigger positive gaps suggest accelerated brain aging. In the Karolinska dataset, worse sleep scores correlated with a wider gap.
To build the sleep score, participants reported on five items: whether they’re morning or evening types, how long they sleep, insomnia symptoms, snoring, and daytime sleepiness.
Add them up, and you land in healthy, intermediate, or poor sleep-health groups. It’s simple, but its association with MRI patterns was striking at this scale.
What might be happening under the hood
The team also looked at blood markers and found that low-grade systemic inflammation explained a slice (just over 10%) of the link between poor sleep and an older-appearing brain.
That doesn’t rule out other mechanisms.
Brain “waste-clearance” processes are most active during consolidated sleep; cut sleep short or chop it into pieces and you may jam those cleanup cycles.
Cardiovascular strain from inadequate sleep can also ripple into brain health over years. As the authors note, these are plausible contributors rather than final answers, but they’re consistent with prior sleep-neuroscience work.
As study author Abigail Dove put it, “Our findings provide evidence that poor sleep may contribute to accelerated brain aging,” adding that sleep is modifiable—meaning there’s something we can do about it.
What counts as a “poor” pattern for night owls
Quick reality check: identifying as a night owl wasn’t the only thing that nudged brain age. It was part of a cluster.
If your natural eveningness leads you to also cut sleep short, fight insomnia, or rely on weekend catch-up, the compounded profile tends to push you toward the riskier end.
Media coverage calling out the one-year average brain-age increase is drawing from the same analysis: the poorest sleepers—many of whom are mismatched night owls—carried that signal.
That dovetails with 2025 longitudinal data showing faster cognitive decline among evening types over a decade, partially mediated by sleep quality and health behaviors. Again, not destiny—but a nudge worth noticing if you routinely burn the midnight oil.
What I’m changing tonight (and what you might try)
News is only useful if we can do something with it. I’m not trying to turn night owls into larks; I’ve written before about respecting your chronotype. But this MRI study gives me a sharper incentive to tighten a few screws I’d gotten lazy about:
– Protect the total sleep window. Evening types often get enough time in bed only if the wake time flexes. If your schedule can’t move, shift the wind-down earlier by 15–20 minutes a night over a week or two. Tiny nudges beat heroic one-night resets.
– Treat snoring and insomnia like real problems. They were in the five-factor score for a reason. If snoring is regular (even without apneas), ask your physician about screening; if insomnia is chronic, cognitive behavioral therapy for insomnia (CBT-I) has the strongest evidence base.
– Mind the evening “stack.” Caffeine after noon, high-intensity workouts late at night, doomscrolling in bed, alcohol as a nightcap—these stack up to erode sleep quality. The inflammation link in the new study nudges me to avoid that stack on weeknights, especially.
And yes, I still love late-night creative sprints. But if they steal tomorrow’s sleep, I’m not just groggy—I’m possibly inching my brain’s biological clock forward.
What we still don’t know
Causality is the headline question. Do bad sleep patterns age the brain, or does a subtly aging brain disturb sleep first? The authors acknowledge both directions could be in play.
Plus, the sleep score was self-reported; MRI was objective, but sleep wasn’t. The UK Biobank sample also tends to be healthier than the general population, which can bias results. These caveats don’t erase the finding—they just set the right level of confidence until replication arrives.
Another open thread: night owls are a diverse bunch. Some evening types protect a full 7–9 hours and keep stellar sleep hygiene. For them, the risk profile may look different than for the classic late-to-bed, early-to-rise pattern.
Future work that teases apart healthy eveningness from sleep-deprived eveningness would help night owls act on data, not stereotypes.
The bottom line
I’m not here to scold anyone out of their chronotype.
But this is one of the largest MRI-based signals yet that poor sleep—and the lifestyle patterns that often accompany eveningness—maps onto brains that look older than they should. That’s the message in the MRI, whether you’re up at dawn or editing photos at midnight.
If you’re a night owl, experiment with the edges you control: a steadier schedule, a wider sleep window, and cleaner evenings. The goal isn’t to turn your life upside down—it’s to keep your brain from quietly racing ahead of the calendar.
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