People who sleep 9 or more hours a day, take midday naps lasting more than 90 minutes, or have poor sleep quality may be at an increased risk of stroke, according to December study findings published in the journal Neurology.
Study author Xiaomin Zhang, MD, PhD, researcher at Huazhong University of Science and Technology, highlighted that the association of longer sleep duration and naps with an increased risk of stroke has yet to find a root cause, “but previous studies have shown that long nappers and sleepers have unfavorable changes in their cholesterol levels and increased waist circumferences, both of which are risk factors for stroke,” said Zhang.
As midday napping is common in China, researchers sought to investigate research from the Dongfeng-Tongji cohort (DFTJ), a study of retired workers that explores the effects of related environment, occupational, lifestyle, and genetic factors, as well as their interactions on the etiology of major chronic diseases in a Chinese occupational population. The study analyzed data from 31,750 DFTJ participants (mean age = 61.7 years) on associations of sleep duration, midday napping, sleep quality, and change in sleep duration with risk of incident stroke and stroke subtypes:
- Participants did not have a history of stroke or other major health problems at baseline, and were followed for an average of 6 years.
- Cox regression models were utilized to estimate hazard ratios (HRs) and 95% CIs for incident stroke.
- After follow-up, 1557 stroke cases were reported.
In the study, participants were asked questions about their sleep and napping habits, with 8% reporting naps lasting more than 90 minutes and 24% reporting sleep durations of 9 or more hours per night. Compared with participants sleeping 7 to less than 8 hours a night, participants who slept 9 or more hours a night had a 23% greater risk of total stroke (HR, 1.23; 95% CI, 1.07-1.41), while shorter sleep (<6 hours a night) revealed no significant association with stroke risk.
Total stroke risk was shown to be 25% higher in participants reporting midday naps lasting longer than 90 minutes compared to naps lasting up to 30 minutes (HR, 1.25; 95% CI, 1.03-1.53). Significant joint effects of sleeping 9 or more hours a night and midday napping longer than 90 minutes were additionally found to increase total stroke risk by 85% (HR, 1.85; 95% CI, 1.28-2.66).
Sleep quality was shown to be a significant factor of stroke risk. Compared with good sleep quality, those reporting poor sleep quality were at a higher risk of total (29%), ischemic (28%), and hemorrhagic (56%) stroke. Joint effects were also significantly found between sleeping 9 or more hours a night and poor sleep quality on risk of total stroke (HR, 1.82; 95% CI, 1.33-2.48).
Study data showed that compared with persistently sleeping 7 to 9 hours a night, those who persistently slept 9 or more hours a night or switched from 7 to 9 hours to 9 or more hours a night had a higher risk of total stroke.
“These results highlight the importance of moderate napping and sleeping duration and maintaining good sleep quality, especially in middle-age and older adults,” Zhang said. Limitations of the study include its use of questionnaire data, as opposed to actual records of participant sleep, as well as a lack of information on sleep disorders such as snoring and sleep apnea.
As Zhang noted that the study only proved an association of longer naps/sleep duration with stroke risk, further studies into the cause and effect of this link is warranted.
Zhou L, Yu K, Yang L, et al. Sleep duration, midday napping, and sleep quality and incident stroke [published online December 11, 2019]. Neurology. doi: 10.1212/WNL.0000000000008739.