Sleep duration is associated with the risk of stroke[13,14], but the incidence of stroke varies considerably among countries and often within a given country[2-5]. Therefore, the relationship between sleep duration and stroke could also vary. The relationship between sleep time and stroke has not been concluded yet in China. This study aimed to study the relationship between sleep duration and stroke in middle-aged and elderly in Guiyang, China. The results strongly suggest that a long sleep duration (>9 h) is independently associated with stroke in middle-aged and elderly people in Guiyang.
In this study, the prevalence of stroke was 2.5% among middle-aged and elderly people aged ≥40 years old in Guiyang, which is similar to that of other regions of China [5,17-19]. The prevalence of stroke in Guiyang was 2.4% for men and 2.6% for women, without significant difference. The prevalence of stroke gradually increased with age, as previously observed, and since age is one of the main risk factors for stroke [5,7,8,17-19]. In addition, the prevalence of stroke in individuals with hypertension, diabetes, and coronary heart disease was 8.1%, 7.5%, and 10.1%, respectively, which was significantly higher than in individuals without these diseases, also supported by previous studies [5,7,8,17-19].
Of the 5065 middle-aged and elderly participants in Guiyang, most (69.4%) had normal sleep duration (7-9 h), 11% had insufficient sleep duration (<7 h), while 19.6% had long sleep duration (>9 h). Age, education, occupation, marital status, health status, sleep quality, smoking status, and drinking status were associated with sleep duration. Moreover, the worse the sleep quality, the greater the proportion of people who have insufficient sleep duration, as observed by previous studies. Sleep duration is a protective factor for sleep quality.
This study showed that the prevalence of stroke in middle-aged and elderly people with different sleep duration was different. The prevalence of stroke in people with normal sleep duration (7-9 h) was the lowest, at 1.8%, while that in people with long sleep duration (>9 h) was 4.7%, which is still higher than that in people with insufficient sleep duration (<7 h) (2.7%). There is a "U" distribution between sleep duration and stroke. This relationship was still observed after adjusting for the other risk factors of stroke. These results are supported by previous studies[11,13,14,20,22,23].
Various reasons might explain the relationship between long sleep and stroke. Long sleep is associated with elevated inflammatory markers[24,25], and inflammation is involved in the pathogenesis of stroke[7,8,26]. Long sleep is also associated with high blood lipid levels[27,28], which directly contribute to atherogenesis. Indeed, the elevated prevalence of metabolic syndrome, carotid artery stenosis, and white matter hyperintensities[31,32] is observed in people with long sleep duration. Furthermore, indirect associations could be that long sleep is associated with a more sedentary life[33,34], which is a risk factor for stroke[7,8]. Long sleep is also associated with depression, sleep apnea, and lower socioeconomic status[12,35,36], which are all risk factors for stroke [7,8]. Future studies should focus on sleep duration, stroke pathogenesis, and molecular epidemiology.
This study has limitations. This study was a cross-sectional survey, preventing any determination of a cause-to-effect relationship. Sleep duration, stroke, and other indicators were reported by the participants, resulting in inevitable subjectivity and biases. No blood parameters were observed in this study. Due to the lack of prospective observation, the causal relationship between sleep duration and stroke disease cannot be obtained, and further epidemiological verification is needed.
In conclusion, a long sleep duration (>9 h) is independently associated with stroke in middle-aged and elderly people in Guiyang. Insufficient sleep was not associated with stroke in this population.