Joint effect of less than 1 h of daytime napping and seven to 8 h of night sleep on the risk of stroke

Background: The joint effect of daytime naps and night sleep on the risk of stroke has not been clarified. Our research aimed to verify this relationship based on data from a large sample-sized cross-sectional study and a cohort study. Methods: The cross-sectional study included 7887 subjects, aged 20-74 years. Using stratified random sampling, 1928 individuals were selected for the cohort study. We then followed up with these individuals for an average of 4.94 years and collected detailed sleep information with the Pittsburgh Sleep Quality Index (PSQI). Serum fasting blood glucose, triglyceride, cholesterol and high density lipoprotein were analyzed, and anthropometric measurements were taken. Interaction and joint analyses were performed. Results: Consistent with the results in the cross-sectional study, hazard ratios (HRs) (95% CI) of stroke were 1.94 (1.21-3.13) and 2.24 (1.05-4.79) for daytime napping >= 1 h and nighttime sleeping >= 9 h in the cohort study. For no naps combined with <7 h of nighttime sleeping, the HR (95%CI) was 2.61 (1.17-5.82). For >= 1 h of naps combined with <7 h, 7-8 h, 8-9 h, and >= 9 h of nighttime sleeping, HRs (95% CI) were 2.16 (1.03-4.51), 2.36 (1.07-5.20), 2.41 (1.11-5.20) and 3.37 (1.05-10.81), respectively. Conclusions: Individuals with 7-8 h of night sleep combined with no daytime naps or less than 1 h of daytime napping were at low risk of stroke; nighttime sleeping >= 9 h combined with daytime napping >= 1 h and night sleep <7 h combined with 0 or >1 h daytime napping was associated with high risk of stroke. Clinical trial registry: http://www.chictr.org. Trail number: ChiCTR-ECH-1200272, ChiCTR-ECH-12002938. (c) 2018 Published by Elsevier B.V.