For some, evenings bring a surge of energy and focus, while others find their peak productivity in the early morning. But a growing body of evidence suggests that identifying as a “night owl” may be linked to poorer cardiovascular health. A large study published on , in the Journal of the American Heart Association adds further weight to this connection.
Researchers followed more than 322,000 adults, aged between 39 and 74, from the UK Biobank for nearly 14 years. They examined the relationship between “chronotype”—an individual’s natural preference for sleep-wake timing—and their risk of cardiovascular disease. Participants self-reported their preferred sleep schedules and were categorized as morning, intermediate, or evening types. Cardiovascular health was assessed using the American Heart Association’s Life’s Essential 8 score, a metric that rates heart health on a scale of 0 to 100 based on eight factors: smoking, diet, exercise, blood sugar, body weight, blood pressure, cholesterol, and sleep quality. Higher scores indicate better cardiovascular health.
Compared with those classified as “intermediate” sleepers, individuals identified as “definite evening” types were 79% more likely to have poor overall scores on the Life’s Essential 8 assessment. They also demonstrated a 16% higher risk of experiencing a heart attack or stroke over the approximately 14-year follow-up period. Conversely, “definite morning” types were 5% less likely than intermediate sleepers to have poor scores.
The question arises: what underlies this association? Does the lifestyle of night owls predispose them to worse heart health, or is there a unique biological component at play?
How Lifestyle May Factor In
The study revealed that night owls generally scored worse on several lifestyle-related factors compared to intermediate sleepers. Specifically, they exhibited 54% higher nicotine exposure, 42% poorer sleep quality, 19% lower physical activity levels, and 8% poorer dietary habits. In contrast, morning types generally reported lower nicotine use and better diets than their intermediate counterparts.
When these lifestyle differences were accounted for, approximately 75% of the increased cardiovascular risk observed in night owls appeared to be attributable to these modifiable factors, rather than the chronotype itself. Among these factors, smoking had the most substantial impact, explaining 34% of the link between late bedtimes and heart disease, followed by poor sleep (14%), high blood sugar (12%), and diet and body weight (11% each).
“The drivers of overall cardiovascular health are modifiable, including nicotine exposure,” explained study lead author Sina Kianersi, a postdoctoral research fellow at Brigham and Women’s Hospital and Harvard Medical School. He added that other influential lifestyle factors included physical activity levels, blood pressure, and cholesterol.
“So for people who identify as night owls, it is a good reason to be even more proactive about those basics,” Kianersi said.
Prior research has suggested that night owls often experience social jet lag, a mismatch between their internal biological clock and their daily routines. This misalignment can contribute to habits like late-night eating, skipped breakfasts, irregular sleep patterns, and increased reliance on caffeine or nicotine. These behaviors, in turn, have been linked to factors that elevate heart disease risk, such as higher body mass index, elevated blood sugar, increased insulin resistance, and lower levels of beneficial cholesterol.
Past research also indicates that adults with irregular sleep patterns, even if they achieve a sufficient total sleep duration, have a 26% higher risk of stroke, heart attack, or heart failure compared to those with regular sleep schedules.
“Fragmented or insufficient sleep can raise blood pressure, cholesterol, and blood sugar, often with weight gain,” said Dr. Bibhu Mohanty, an associate professor at the University of South Florida who was not involved in the research. “This is largely driven by [the stress hormone] cortisol, which mobilizes sugar and fat in ways that can make disease harder to reverse, once it is established.”
The Biology of Night Owls
Being a night owl isn’t simply a matter of choice—it’s partly determined by genetics. Studies have identified hundreds of genetic variants linked to chronotype, many of which are involved in regulating the body’s 24-hour circadian rhythms. These rhythms control sleep, appetite, hormone cycles, and heart function throughout the day and night.
Individuals with late chronotypes often experience delayed circadian rhythms, meaning their melatonin levels rise later in the evening, and their cortisol levels peak later in the morning. This shift can disrupt the body’s alignment with the natural day-night cycle, potentially leading to an overactive fight-or-flight response. Blood pressure may remain elevated at night, and inflammation and oxidative stress may increase, potentially damaging blood vessels, disrupting blood sugar, and promoting plaque buildup in the arteries.
Many of the genes involved in determining chronotype also directly affect lipid and glucose metabolism, or how the body processes fats and sugars. Studies show that evening types exhibit altered expression of these “clock genes” alongside elevated inflammation markers and triglycerides, a type of fat, compared to morning types. These patterns may contribute to metabolic issues like insulin resistance and poor cholesterol, though further research is needed to confirm the direct link.
Emerging evidence suggests that there may also be subtle differences in heart structure and function in night owls, though the long-term effects of these differences are still being investigated.
The UK Biobank study also indicated a potential stronger link between night owl status and poorer heart health in women compared to men. Female night owls were 96% more likely, while male night owls were 67% more likely, to have a poor overall cardiovascular health profile based on the Life’s Essential 8 score. Kianersi noted that this difference could reflect social pressures, biological factors, or a combination of both, warranting further investigation.
Even with the observed association between chronotype and poorer heart health, being a night owl doesn’t necessarily condemn someone to cardiovascular disease. Kianersi emphasized the need for studies that explore cause-and-effect relationships, utilizing approaches like genetic analysis and intervention research. He also highlighted the importance of examining these patterns in younger adults and diverse populations with varying work schedules and environments.
For night owls seeking to protect their heart health, Mohanty advises prioritizing improvements in lifestyle habits. “That means developing healthier sleep routines, exercising, making healthy dietary choices, avoiding unnecessary snacking and smoking, and potentially using medication to reduce risk if needed,” he said. He concluded that a holistic approach to heart health is “probably the best approach to limit risk.”
