We find sparsity in studies that explore the interrelation between overall and subtypes of strokes and sleeping periods. Furthermore, those studies cannot be decisive, and the relationship between sleeping time and stroke risks cannot be proved to be causal. Thus, a new study was carried out to inquire into the causality, not only through observation methods by a cohort study but also using MR, Mendelian randomization. Some other reviews were done, but none adopted the MR design, making this study the most accurate. MR is an epidemiological method that uses genetic traits to evidence any causal relation. And therefore, variables, like other side effects of sleep, can’t affect the results because those factors don’t influence genetics.
The study involved 79k+ persons aged between 45 and 79 years, who were followed up for about 14 years. Results showed that long sleep hours (>=9 hr/day) is collateral with a higher risk of stroke; the total stroke (hazard ratios, 1.12) and ischemic stroke (hazard ratios, 1.14). In comparison, a short sleep period (<7 hr/day) is collateral with higher risks of intracerebral hemorrhage, aka ICH (hazard ratio, 1.21). On the other hand, the 2-sample MR did not support those results, but it showed a correlation between short sleep periods and a high risk of LAS, a large-artery atherosclerotic stroke. And the latter still needs to be explored further in the future.
In conclusion, the risk of ischemic and total stroke was higher in people who slept 9 hours and above per day, while ICH was detected more in people who slept less than 7 hr/day. As to the MR design, those results weren’t confirmed, but a correlation was seen in short and long sleeping periods with strokes.