In this large and extended follow-up after a period of > 15 years, robust associations were assessed even after comprehensive multivariable adjustment. The main findings of the current study were as follows. (1) Prolonged sleep duration (> 8 h) was independently associated with an increased risk of all-cause mortality compared with the reference group with 7–8 h of sleep. (2) Both prolonged sleep duration (> 8 h) with regular sleep and irregular sleep patterns combined with short sleep duration (< 7 h) were independently associated with an increased risk of all-cause mortality compared to the reference group (7–8 h with regular sleep). (3) In sex-stratified analyses, women with long and irregular sleep patterns and men with either long and regular or short and irregular sleep showed a significantly increased risk of all-cause mortality. (4) In age-stratified analyses, short sleep duration was generally associated with increased risk in participants aged 40–49 years, whereas prolonged sleep duration was associated with worse outcomes in those aged ≥ 60 years.
Cardiovascular diseases remain the leading cause of death worldwide, with modifiable risk factors playing crucial roles in disease progression and prevention23. While traditional risk factors such as hypertension, obesity, smoking, and sedentary lifestyles are well-documented24 the influence of sleep health is often underappreciated. Emerging epidemiological and mechanistic studies suggest that both insufficient and excessive sleep duration, poor sleep quality, and sleep disorders such as obstructive sleep apnea contribute to adverse cardiovascular outcomes 1,3,8,9,10,11,25,26,27,28,29,30,31,32,33,−34. The bidirectional relationship between sleep disturbances and cardiovascular pathology highlights the need for a comprehensive approach to address sleep health in preventive and clinical care8,9,10,11,35. Furthermore, all-cause mortality, a broad indicator of population health, is also strongly linked to sleep patterns8,9,11,25,26,27,28,30,31,32,33,−34. Our findings are consistent with previous studies. The present study also found that deviations from the 7–8-h sleep range were associated with increased mortality risk.
However, earlier studies focused primarily on sleep duration without incorporating the regularity or quality of sleep into their analytical framework6,9,10,11,25,27,28,32,33,35. We simultaneously evaluated sleep duration, sleep regularity, self-reported sleep sufficiency, and their combined effects on mortality and cardiovascular outcomes in a large, well-characterized, population-based cohort with long-term follow-up. Previous studies have reported increased mortality associated with short sleep duration6,9,10,11,25,27,28,32,33,35; however, the present study demonstrated that mortality was particularly elevated among individuals with short sleep durations accompanied by irregular sleep patterns. In contrast, long sleep duration showed an adverse association regardless of sleep regularity. Our findings established that irregular sleep patterns, particularly when combined with either short or long sleep durations, were associated with elevated mortality risk, highlighting the importance of sleep regularity as an independent risk factor. Although the underlying mechanisms remain unclear, these observations warrant further investigation to elucidate the causal pathways linking combined sleep patterns to adverse health outcomes.
Furthermore, we conducted sex-stratified analyses and revealed distinct patterns in men and women, where short irregular sleep duration was more detrimental to men, whereas long irregular sleep duration had a stronger association with mortality and MACE in women. The precise mechanisms underlying the observed sex-specific patterns remain incompletely understood, yet several plausible hypotheses warrant consideration. Hormonal regulation of sleep, including sex hormone effects, may contribute to differences in sleep-related outcomes between men and women. In women, hormonal transitions and greater exposure to psychosocial stress and caregiving responsibilities may impact sleep patterns36. In men, higher prevalence of sleep-disordered breathing, work-related stress such as long working hours may also play a role37. Additionally, short sleep duration was generally associated with increased risk in the younger age group, while long sleep duration was linked to worse outcomes in older adults38. This aligns with previous studies indicating stronger associations between long sleep and poor outcomes in older adults, although age- and sex-specific patterns remain underexplored. These findings underscore the potential value of incorporating sex- and age-specific considerations into sleep-related risk assessments and highlight the need for personalized approaches to sleep health in both clinical practice and public health strategies. Future research should further explore these mechanisms to better inform tailored interventions.
Taken together, these findings suggest that the optimal sleep duration may differ by demographic characteristics. While 7–8 h of sleep remains a broadly recommended range, our age-stratified results suggest that middle-aged individuals (particularly those aged 40–49 years) may be more vulnerable to short sleep duration, whereas older adults (≥ 60 years) appear to be more susceptible to the adverse effects of prolonged sleep. Similarly, sex-specific analyses indicate that men may be more affected by short and irregular sleep, whereas women are more vulnerable to long and irregular sleep patterns. These results support the development of individualized sleep health strategies that incorporate both sleep duration and regularity, tailored to age and sex.
In addition to clinical outcomes, the baseline characteristics across sleep duration groups revealed distinct sociodemographic patterns. Participants with prolonged sleep duration (> 8 h) were generally older, had a higher prevalence of comorbidities such as hypertension and diabetes, and were more likely to have lower education and income levels. Participants with short sleep duration (< 7 h) were younger, more likely to reside in urban areas, and had higher education and income levels. These findings suggest that sleep patterns may reflect not only the underlying health status but also broader lifestyle and social factors, which may help explain their differential associations with mortality risk. Although these comorbidities and socioeconomic factors were carefully adjusted, the possibility of residual confounding remained. Despite this, the existence of a direct causal relationship between sleep patterns and cardiovascular disease has not been conclusively established and requires further investigation.
Short sleep duration has well-known mechanisms linked to increased mortality. Sleep deprivation can lead to impaired glucose tolerance, elevated evening cortisol levels, heightened sympathetic nervous system activity, and reduced leptin secretion, potentially contributing to diabetes, hypertension, and obesity38,39,40,41. Thus, chronic sleep restriction can negatively influence overall health outcomes and increase the risk of chronic diseases and mortality.
However, the exact mechanisms linking increased self-reported sleep duration with higher mortality rates remain unclear. One proposed explanation is that prolonged self-reported sleep may reflect an individual’s increased need for sleep, which is indicative of reduced physiological reserves and a diminished ability to survive critical illnesses. Supporting this view, previous research has shown that individuals sleeping for approximately 7 h had a 10% increased risk of myocardial infarction compared to those sleeping for 8 h; however, the subsequent risk of mortality from myocardial infarction was 17% lower42. Additionally, prolonged sleep duration may indicate underlying undiagnosed health conditions or unmanaged comorbidities, such as obstructive sleep apnea, potentially elevating the risk of cardiovascular events and mortality42,43. Individuals initially experiencing insufficient sleep may extend their sleep duration as a compensatory response, eventually developing long sleep patterns associated with lower sleep efficiency, which is another factor linked to increased mortality risk.
Our study had several strengths. First, we used large-scale data with long-term follow-up to enhance the robustness of our findings. Second, our analysis comprehensively addressed overall sleep health by including not only sleep duration, but also sleep regularity and self-reported sufficiency. Third, we actively adjusted for numerous important factors, including key clinical variables (e.g., sex, BMI, hypertension, diabetes), detailed socioeconomic factors (e.g., income, education, and area of residence), and physical activity levels. These factors allowed us to thoroughly explore and control for differences in socioeconomic status across sleep patterns. Finally, our study highlighted notable sex-based differences in associations with poor sleep patterns, providing further insight into sleep-related health disparities.
This study has several limitations. First, given the observational nature of the study, we cannot infer the causality between sleep patterns and the risk of all-cause mortality or cardiovascular outcomes. Although we adjusted for a wide range of potential confounders, the possibility of residual confounders from unmeasured or imprecisely measured variables cannot be excluded. In particular, sleep disorders, such as obstructive sleep apnea, which may influence both sleep patterns and cardiovascular outcomes, were not objectively assessed in this study. This limitation could have led to the misclassification of sleep quality or underestimation of associated risks. Second, sleep duration and regularity were assessed using self-reported questionnaires, which are subject to recall bias and misclassification. Moreover, the assessment of sleep regularity did not distinguish between weekday and weekend patterns; thus, potential circadian misalignment could not be captured. Such non-differential misclassification is likely to bias the results toward null, potentially underestimating the true associations. Additionally, objective sleep measurements such as actigraphy or polysomnography were not available, limiting the precision of sleep pattern assessment. Third, we assessed baseline sleep characteristics only once without accounting for changes in sleep behavior over a long follow-up period. Repeated measurements may better capture the dynamic nature of sleep and its effects on health. Finally, although we adjusted for extensive socioeconomic factors, we did not fully assess other potential determinants of sleep duration such as intrinsic sleep needs, work schedules, psychological stress, and environmental influences, all of which could differentially impact health outcomes.
In conclusion, this large prospective cohort study found a complex association between sleep duration, regularity, and mortality. Long sleep durations were associated with an increased risk of mortality among individuals with regular sleep, whereas short sleep durations were associated with higher risk among those with irregular sleep. Although the interaction between sex and sleep patterns was not statistically significant, stratified analyses suggested potential sex-specific trends. These patterns may help inform tailored sleep health strategies that consider both sleep characteristics and sex.