A UK Biobank study of 322,000 adults found that evening chronotypes had 79% higher odds of poor cardiovascular health and 16% higher risk of cardiac events over 14 years. The risk stemmed from lifestyle behaviours linked to social jetlag, not from being a night owl itself.
Being a night owl is not inherently dangerous for your heart. But living like a night owl in a world built for early risers appears to be.
A study published in the Journal of the American Heart Association in January 2026 analysed data from 322,000 UK Biobank participants over a median follow-up of 14 years. The researchers classified participants by self-reported chronotype — whether they considered themselves morning people, evening people, or somewhere in between — and then tracked cardiovascular outcomes including heart attack, stroke, and heart failure.
The Numbers
Evening chronotypes had 79% higher odds of poor cardiovascular health compared to morning types, scored against the American Heart Association's Life's Essential 8 metrics. They also had a 16% higher risk of experiencing a cardiac event during the follow-up period.
But the data pointed away from biology as the explanation. When the researchers adjusted for behavioural factors — smoking, alcohol consumption, diet quality, physical activity, and sleep regularity — the association weakened substantially. Night owls in the study were more likely to smoke, drink more alcohol, eat later, exercise less, and sleep irregular hours. These behaviours, not some internal clock malfunction, drove most of the excess risk.
Social Jetlag Is the Mechanism
The concept that ties this together is social jetlag: the mismatch between a person's biological sleep-wake preference and the schedule society demands. An evening chronotype who has to wake at 6:30 AM for work accumulates chronic sleep debt during the week and oversleeps on weekends. That pattern disrupts metabolic regulation, raises cortisol, and increases inflammation — all of which feed into cardiovascular risk.
The effect was more pronounced in women, though the study did not fully explain why. Hormonal differences in how circadian disruption affects metabolism may play a role, but this remains speculative.
The study is available in full from JAHA.
Chronotype Is More Complicated Than "Morning" or "Evening"
A separate study from McGill University identified five distinct sleep-wake profiles rather than the traditional two. These ranged from consistently early sleepers to irregular sleepers whose schedules shifted daily. The irregular group showed the worst health outcomes, reinforcing that consistency matters more than whether you prefer mornings or evenings.
Research from Toronto Metropolitan University added another layer: among people who used screens before bed, the content mattered more than the screen use itself. Passive scrolling through stressful news content was associated with worse sleep outcomes than watching calm or neutral material. The light from the screen was less of a factor than what was on it.
What This Means Practically
If you are an evening chronotype, the research does not say your biology is a cardiovascular risk factor. It says the mismatch between your biology and your schedule creates downstream behaviours that are. The actionable parts are the behaviours themselves:
- Sleep consistency matters more than total sleep time. Keeping wake times within a 60-minute window, even on weekends, reduces social jetlag.
- Meal timing affects metabolic health independently of diet quality. Eating your last meal 2-3 hours before bed aligns better with circadian metabolic rhythms.
- Light exposure in the morning helps shift circadian phase earlier, reducing the severity of the mismatch for evening types who need to wake early.
None of this requires changing your chronotype — which is largely genetic and resistant to forced change anyway. It requires managing the friction between your chronotype and your schedule.
Jessica Williams
