Abstract
BACKGROUND: Sleep represents a key modifiable risk factor for cardiovascular diseases (CVDs). Although previous studies have examined separate associations of nighttime sleep duration and napping duration with CVDs, few have investigated their combined effects or elucidated how this association differs across age or gender. This study aimed to assess how different sleep combinations influence the CVD risk. METHODS: This study used longitudinal data from the China Health and Retirement Longitudinal Study (CHARLS) collected between 2011 and 2020. Baseline information on sleep and other relevant variables was obtained through self-reported questionnaires, and incident CVDs were identified during follow-up. Cox proportional hazards regression models were applied to evaluate independent and combined effects of nighttime sleep duration and napping duration on CVD incidence. Stratified analyses by age and gender explored potential heterogeneity, and sensitivity analyses were conducted to test result robustness. RESULTS: A total of 7,975 participants were included, of which 2,117 participants (26.55%) developed CVDs after follow up. After adjusting for confounders, insufficient nighttime sleep (< 6 h) was independently associated with a higher risk of CVDs (hazard ratio [HR]: 1.189, 95% confidence interval [CI]: 1.071-1.319). Compared with participants having moderate nighttime sleep without napping, those with < 6 h/night without napping (HR: 1.177, 95% CI: 1.021-1.357), < 6 h/night with napping duration ≤ 0.5 h (HR: 1.558, 95% CI: 1.236-1.962), and < 6 h/night with napping duration > 1 h (HR: 1.300, 95% CI: 1.020-1.655) had significantly higher CVD risk. Among these, the combination of < 6 h/night with napping duration ≤ 0.5 h was associated with the highest observed CVD incidence. Stratified analysis revealed significant heterogeneity by gender, with less pronounced associations between sleep combinations and CVD risk in men compared with those in women. Sensitivity analyses supported the robustness of findings. CONCLUSIONS: Adequate nighttime sleep is associated with lower CVD risk. Most combinations of insufficient nighttime sleep and daytime nap increased CVD risk among middle-aged and older adults. However, the combination of insufficient nighttime sleep with moderate napping was not associated with increased CVD risk in this population. These results provide a scientific foundation for targeted sleep interventions and clinical guidance.