Introduction: Sleep quality could be an important risk factor for cardiovascular disease, beyond the influence of sleep duration. In particular, difficulty falling asleep, a symptom of poor sleep quality, may be associated with cardiovascular disease; however, evidence in Asian populations is limited. Objective: To examine the association between difficulty falling asleep and incident major cardiovascular events (MACE) beyond the effect of sleep duration in the general population. Methods: We followed 2,507 participants (1,038 men and 1,469 women) enrolled in the NIPPON DATA 2010 study in 2010, excluding those with prior cardiovascular events, until December 31, 2019. Sleep information was obtained from self-administered questionnaires and assessed by difficulty falling asleep (frequent, occasional/rare, none) and sleep duration (short: <6, moderate: 6–<8, long: ≥8 hours). The outcome was incident MACE (stroke, myocardial infarction, PCI, or heart failure). Hazard ratios (HRs) for difficulty falling asleep and sleep duration were estimated using Cox proportional hazards models adjusted for sex, age, BMI, diabetes, hypertension, dyslipidemia, smoking, alcohol use, K6 score, and physical activity index. Both sleep variables were included in the same model for mutual adjustment. Results: During the 8.3-year observation period, 118 MACE occurred (72 in men, 46 in women). The mean age was 58.1±15.8 years. In the overall analysis, compared with those who frequently had difficulty falling asleep, the HRs (95% CIs) were 0.54 (0.33–0.88) for participants who occasionally or rarely had difficulty and 0.51 (0.26–0.99) for those who never had difficulty. For sleep duration, compared with those with moderate sleep duration, the HR (95% CI) was 0.79 (0.49–1.29) for participants with short sleep duration and 1.48 (0.91–2.41) for those with long sleep duration. In analyses stratified by sex, women with long sleep duration showed a higher HR HR (95% CI) = 2.70 (1.25-5.83), while this pattern was not observed in men. Conclusions: This study found that participants with frequent difficulty falling asleep had a higher risk of MACE in both sexes, independent of sleep duration, whereas long sleep duration increased the risk among women. Our findings suggest that evaluating difficulty falling asleep as an indicator of sleep quality is important for cardiovascular risk assessment, as well as sleep duration.
Hirata et al. (Tue,) studied this question.