A comprehensive investigation drawing upon a substantial cohort of over 300,000 individuals has illuminated a compelling correlation between an individual’s inherent preference for late-night activity and a heightened susceptibility to cardiovascular ailments, particularly as they advance in age. This observed association appears to exert a more pronounced influence on women, underscoring a potential gender-specific vulnerability. The research, meticulously detailed in the latest issue of the Journal of the American Heart Association, a distinguished open-access, peer-reviewed publication, posits that the timing of an individual’s peak daily activity may constitute a critical determinant of their long-term cardiac well-being.
Delving into the intricate tapestry of human biological timing, the study meticulously analyzed extensive health data sourced from the UK Biobank, encompassing participants with an average age approximating 57 years. The core of this inquiry centered on the concept of chronotypes – the innate proclivities of individuals concerning their sleep and wake cycles – and their potential interplay with cardiovascular health metrics. Participants were meticulously categorized based on their self-declared diurnal patterns. A distinct segment, comprising approximately 8% of the study population, identified themselves as "definitely evening people." These individuals characteristically engaged in their most vigorous activities later in the day and retired for the night at considerably later hours, often around 2 a.m. Conversely, a more substantial proportion, around 24%, identified as "definitely morning people." This group exhibited a propensity for earlier awakenings, earlier bedtimes (frequently around 9 p.m.), and a peak in their daily energy levels during the morning hours. The remaining 67% of participants, who did not report a strong inclination towards either extreme, were classified as possessing an "intermediate" chronotype, indicating a less defined or more balanced pattern of sleep and activity.
The evaluation of cardiovascular health within this extensive dataset was rigorously conducted utilizing the American Heart Association’s established Life’s Essential 8™ framework. This comprehensive scoring system systematically assesses a spectrum of behavioral and physiological factors recognized as pivotal for maintaining robust heart health. These factors encompass adherence to a nutritious dietary regimen, consistent engagement in physical activity, the absence of tobacco use, and the attainment of restorative, high-quality sleep. Furthermore, the framework critically examines key physiological indicators such as maintaining healthy body weight, optimal cholesterol levels, balanced blood sugar concentrations, and appropriate blood pressure readings.
A comparative analysis of these chronotype groups revealed several striking divergences in their cardiovascular health profiles. When contrasted with individuals classified as having an intermediate chronotype, those designated as "evening people," colloquially referred to as night owls, demonstrated a significantly elevated likelihood of exhibiting an overall suboptimal cardiovascular health score, registering a 79% greater probability. This predisposition extended to a tangible increase in the risk of experiencing serious cardiac events; night owls exhibited a 16% higher incidence of heart attack or stroke over a median follow-up period that spanned approximately 14 years. Notably, the observed link between an evening chronotype and diminished cardiovascular health scores was demonstrably more pronounced among female participants compared to their male counterparts.
Further dissection of the data indicated that a substantial portion of the amplified risk of cardiovascular disease observed in individuals with evening chronotypes could be attributed to lifestyle choices. Specifically, the patterns of nicotine consumption and insufficient or disrupted sleep emerged as significant contributing factors. In a stark contrast, "morning people," often characterized as early birds, displayed a more favorable cardiovascular profile. They exhibited a 5% lower prevalence of poor cardiovascular health scores when juxtaposed with individuals who did not exhibit a strong preference for either morning or evening activity.
The underlying mechanisms contributing to the increased cardiovascular vulnerability among evening chronotypes are believed to be multifaceted, with circadian misalignment playing a central role. Dr. Sina Kianersi, a lead author of the study and a research fellow at Brigham and Women’s Hospital and Harvard Medical School, explained that "Evening people often experience circadian misalignment, meaning their internal body clock may not match the natural day-to-night light cycle or their typical daily schedules." This internal discordance can create a cascade of challenges, potentially leading to a greater propensity for behaviors detrimental to cardiovascular health. As Dr. Kianersi elaborated, "Evening people may be more likely to have behaviors that can affect cardiovascular health, such as poorer diet quality, smoking and inadequate or irregular sleep." Consequently, this misalignment can impede their ability to consistently adopt and maintain lifestyle habits that are crucial for long-term cardiac well-being.
Despite these concerning findings, the research offers a glimmer of hope and actionable insights for individuals who naturally gravitate towards later schedules. Kristen Knutson, Ph.D., FAHA, who chairs the American Heart Association’s 2025 scientific statement on the role of circadian health in cardiometabolic health and disease risk, and who was not involved in the current study, emphasized that "These findings show that the higher heart disease risks among evening types are partly due to modifiable behaviors such as smoking and sleep. Therefore, evening types have options to improve their cardiovascular health." Dr. Knutson further clarified that "Evening types aren’t inherently less healthy, but they face challenges that make it particularly important for them to maintain a healthy lifestyle." This perspective underscores the importance of recognizing that while chronotype may present inherent challenges, proactive lifestyle management can significantly mitigate associated risks.
The implications of this research extend to the realm of clinical practice, suggesting a paradigm shift towards personalized healthcare interventions that acknowledge and incorporate an individual’s chronotype. The aforementioned American Heart Association scientific statement, spearheaded by Dr. Knutson, advocates for the integration of chronotype considerations into the planning of therapeutic strategies and lifestyle modification programs. "Some medications or therapies work best when they align with a specific time of relevant circadian rhythms, and this time will vary depending on whether you are a morning, intermediate, or evening chronotype," Dr. Knutson explained. She further proposed that "Targeted programs for people who naturally stay up late could help them improve their lifestyle behaviors and reduce their risk of cardiovascular disease." This tailored approach holds the promise of optimizing treatment efficacy and empowering individuals to proactively manage their cardiovascular health in a manner that aligns with their biological predispositions.
It is imperative to acknowledge certain limitations inherent in the study’s design. The overwhelming majority of participants in the UK Biobank cohort were of white ethnicity, and as a group, they tended to be healthier than the general population. This demographic composition may constrain the generalizability of the findings to more diverse populations and those with different health statuses. Additionally, the assessment of chronotype was conducted only once, relying on self-reported data rather than objective, repeated measurements, which could introduce a degree of variability or bias. The research initiative received partial financial support from the American Heart Association, underscoring its commitment to advancing the understanding of cardiovascular health.
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