New research suggests that being a “night owl” may carry significant risks for cardiovascular health, particularly for women. A large-scale study analyzing teh habits of over 300,000 adults found those with a preference for later bedtimes experienced a nearly 80% greater prevalence of poor cardiovascular health and a 16% increased risk of heart attack or stroke over a 14-year period [[1]].The findings underscore the importance of considering individual chronotypes – a person’s natural inclination to sleep – when assessing and addressing heart health risks.
Adults who prefer to stay up late may face a significantly higher risk of cardiovascular problems, particularly women, according to a new study. The research highlights the importance of considering individual sleep patterns when assessing heart health and developing preventative strategies.
Middle-aged and older adults who identify as “night owls” experience poorer cardiovascular health compared to those who are more active during the day, a study published in the Journal of the American Heart Association, the peer-reviewed journal of the American Heart Association.
Researchers analyzed health data from over 300,000 adults – with an average age of 57 – from the UK Biobank, one of the world’s most comprehensive biomedical databases, to understand how chronotypes – an individual’s natural inclination toward sleep timing – impact cardiovascular health.
Chronotypes: Morning, Evening, and Intermediate
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Approximately 8% of participants described themselves as “definitely evening types,” meaning they tend to go to bed late, such as around 2 a.m., and are more active later in the day.
Those who identified as “definitely morning types” – representing nearly a quarter of the participants – reported being more active earlier in the day and going to bed earlier, around 9 p.m.
Around 67% of participants were categorized as having an “intermediate” chronotype, indicating they didn’t strongly identify as either morning or evening people.
Increased Cardiovascular Risk in Evening Types
The study assessed cardiovascular health based on factors including diet, physical activity, tobacco use, sleep quality, and levels of weight, cholesterol, blood sugar, and blood pressure.
The analysis revealed that, compared to those with an intermediate chronotype, “evening types” had a 79% greater prevalence of poor overall cardiovascular health.
Furthermore, night owls had a 16% increased risk of experiencing a heart attack or stroke over a median follow-up period of approximately 14 years, compared to individuals in the intermediate category.
The study also found that the association between an evening chronotype and poorer cardiovascular health was more pronounced in women than in men.
Circadian Misalignment and Unhealthy Habits
Much of the increased cardiovascular risk among night owls is likely due to unhealthy habits and existing heart health factors, particularly nicotine use and inadequate sleep.
Conversely, “morning types” showed a 5% lower prevalence of poor cardiovascular health scores compared to other groups.
“Evening types often experience circadian misalignment, meaning their internal body clock may not align with the natural light-dark cycle or their typical daily schedules,” explained Sina Kianersi, lead author of the study and an associate researcher in the division of sleep medicine and circadian disorders at Brigham and Women’s Hospital and Harvard Medical School, both in Boston.
“Evening types are more likely to engage in behaviors that can negatively affect cardiovascular health, such as a poorer diet, smoking, and insufficient or irregular sleep.”
Options for Improving Cardiovascular Health
However, the study’s findings aren’t entirely discouraging for night owls, noted Kristen Knutson, chair of the American Heart Association’s 2025 statement, who was not involved in the research.
“These findings suggest that the greater risks of heart disease among evening chronotypes are partly attributable to modifiable behaviors like smoking and sleep,” Knutson said. “Therefore, these individuals have opportunities to improve their cardiovascular health.”
In fact, the American Heart Association’s scientific statement, led by Knutson, suggests that individual chronotype should be considered when choosing interventions or treatments. “Some medications or therapies work best when aligned with a specific time of day relative to relevant circadian rhythms, and this timing will vary depending on whether you are a morning, intermediate, or evening chronotype.”
The authors noted some limitations to the study, including the fact that the majority of participants in the UK Biobank were white and generally healthier than the general population. They also pointed out that preference for being a morning or evening person was measured only once and was self-reported.
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