Middle-aged and older adults who tend to be more active in the evening have poorer cardiovascular health than those who are active earlier in the day. This association appears to be more pronounced in women, according to a new study published in the Journal of the American Heart Association. The findings suggest that the time of day when people are most active may play an important role in long-term heart health.

Study Examines Sleep Habits of More Than 300,000 Adults

The researchers examined health data from more than 300,000 adults (average age approximately 57) registered with the UK Biobank. The analysis focused on chronotypes, which describe a person’s natural preference for sleep and wake times, and how these preferences relate to cardiovascular health.

Participants were divided into groups based on their self-reported circadian rhythms. About 8% described themselves as “clear evening people,” meaning they typically went to bed very late (e.g., at 2 a.m.) and reached their peak activity later in the day. About 24% identified as “clear morning people,” who tended to wake up earlier, go to bed earlier (e.g., at 9 p.m.), and be most active earlier in the day. The remaining 67% were classified as “intermediate” chronotypes if they were unsure or reported being neither clearly morning nor evening people.

Cardiovascular health was assessed using the American Heart Association’s Life’s Essential 8™ metrics. This framework considers behaviors and health factors known to support heart health, including healthy eating, physical activity, not smoking, and good sleep. This also includes maintaining a healthy body weight, cholesterol level, blood sugar level, and blood pressure.

Significant Differences Between Night Owls and Early Risers

When comparing the chronotype groups, the researchers found several striking patterns: Compared to people in the middle category, those classified as “evening people” and often referred to as night owls were 79% more likely to have poor overall cardiovascular health.

Night owls also had a 16% higher risk of suffering a heart attack or stroke during a median follow-up period of approximately 14 years. The association between the evening chronotype and poorer heart health scores was more pronounced in women than in men.

Much of the increased risk of heart disease among evening types was related to lifestyle habits, particularly nicotine use and insufficient sleep. In contrast, “morning people,” also known as early risers, had a 5% lower prevalence of poor cardiovascular health than people without a pronounced preference for morning or evening.

Why Evening Types May be at Increased Risk for Heart Disease

“Evening people often suffer from circadian misalignment, which means that their internal clock may not be in sync with the natural day-night light cycle or their typical daily routine,” said lead study author Sina Kianersi, Ph.D., D.V.M., a research scientist in the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital and Harvard Medical School, both in Boston. “Evening people may be more prone to behaviors that can affect cardiovascular health, such as poorer diet, smoking, and insufficient or irregular sleep.” This misalignment may make it difficult for night owls to maintain habits that support long-term heart health.

Lifestyle Changes Could Lower Risk

The findings are not entirely discouraging for people who like to stay up late, according to Kristen Knutson, Ph.D., FAHA, honorary chair of the American Heart Association’s 2025 statement titled “Role of Circadian Health in Cardiometabolic Health and Disease Risk” (The Role of Circadian Health in Cardiometabolic Health and Disease Risk), are not entirely discouraging for people who like to stay up late. Knutson was not involved in the study.

“These findings show that the higher risk of heart disease among evening types is partly due to modifiable behaviors such as smoking and sleep. Therefore, night owls have opportunities to improve their cardiovascular health,“ she said. ”Night owls are not inherently less healthy, but they face challenges that make it especially important for them to maintain a healthy lifestyle.”

Tailoring Treatment to the Internal Clock

The American Heart Association’s scientific statement, led by Knutson, also recommends taking chronotype into account when planning treatments or lifestyle interventions. “Some medications or therapies work best when timed to a specific period of relevant circadian rhythms, and that time varies depending on whether you are a morning, intermediate, or evening chronotype,” she said. “Targeted programs for people who naturally stay up late could help them improve their lifestyle behaviors and reduce their risk of cardiovascular disease.”

For drug therapies, this means that efficacy and side effects may depend on whether a drug is synchronized with the individual’s circadian phase. For example, the optimal time to take blood pressure medication or statins may vary depending on when relevant physiological processes peak for each chronotype. An inappropriate time of administration may reduce efficacy or inadequately lower cardiovascular risk, even though the drug itself is correctly selected.

Lifestyle interventions such as sleep hygiene, exercise, and nutrition also benefit from being tailored to the chronotype. Many general recommendations are implicitly geared toward morning chronotypes, which often leads to chronic sleep deprivation, social jet lag, and increased stress in evening chronotypes. These factors, in turn, are associated with an increased risk of high blood pressure, metabolic disorders, and inflammatory processes. Tailored programs for people with a late chronotype therefore focus less on forcibly shifting the daily rhythm earlier and more on regularity, targeted light control, physical activity at biologically favorable times, and sensibly distributed food intake.

The American Heart Association’s key message is therefore that personalized, chronobiologically informed interventions have the potential to improve adherence and reduce the risk of cardiovascular disease. Instead of making people work against their internal clock on a permanent basis, adapting therapies and preventive measures to individual chronotypes can lead to sustainably better health outcomes. The researchers pointed out that most UK Biobank participants were white and generally healthier than the general population, which could limit the generalizability of the results to other groups. In addition, chronotype was assessed only once and was based on self-reported information rather than repeated measurements.