Sleeping more than 9 hours a night or taking long midday naps were each associated with increased risk of incident stroke in a large, prospective cohort study.
Compared with 7 to 8 hours of sleep, 9 or more hours increased the risk of stroke by 23% (HR 1.23; 95% CI 1.07–1.41), while 6 hours of sleep had no significant effect on stroke risk, reported Xiaomin Zhang, MD, PhD, of Huazhong University of Science and Technology in Wuhan, China, and colleagues.
A regular midday nap lasting more than 90 minutes also boosted stroke risk by 25% (HR 1.25; 95% 1.03–1.53) compared with napping for a half-hour or less, they reported in Neurology.
What drives this connection is unclear, 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,” Zhang said in a statement. Long napping and sleeping also may suggest an overall inactive lifestyle, Zhang added.
The study adds to a growing picture of the role sleep plays in cardiovascular health, said Jessica Lunsford-Avery, PhD, of Duke University Medical Center, who wasn’t involved with the study.
“When people think about sleep problems, they often think about difficulties with getting enough sleep,” Lunsford-Avery told MedPage Today. “But this study and others indicate that the relationship between sleep and cardiovascular health is complex, and indeed, short sleep is not consistently linked with cardiovascular risk.”
In prior research, Lunsford-Avery and coauthors showed that irregular sleep patterns were tied to stroke and cardiovascular risk over a 10-year period. This study may indicate something similar, she noted: “Naps are a component of irregular sleep patterns, so it’s possible that, in addition to long sleep duration, irregular sleep patterns are playing a role here as well.”
In their study, Zhang and colleagues looked at a cohort of 31,750 retired employees of the Dongfeng Motor Corporation in China who had an average baseline age of about 62, following them for an average of 6.2 years.
Participants had no history of coronary heart disease, cancer, or stroke, and were asked to complete a questionnaire outlining their usual sleeping and napping patterns and rating their sleep quality.
In total, 23.9% reported long sleeping (more than 9 hours) and 7.6% reported long midday napping (more than 90 minutes). Midday napping is common in China, Zhang noted.
Over the followup period, 1,557 incident stroke cases emerged, mainly ischemic. Compared with people who reported good sleep quality, those with poor sleep quality showed a 29% higher risk of total stroke (HR 1.29; 95% CI 1.09-1.52).
The researchers also saw joint effects: people who were both long nappers and long sleepers were 85% more likely to have a stroke than people who were moderate sleepers and nappers (HR 1.85; 95% CI 1.28–2.66), for example. Similarly, people who were long sleepers and had poor sleep quality had an 82% increased stroke risk (HR 1.82; 95% CI 1.33–2.48) over moderate sleepers with good sleep quality.
Switching from being a moderate sleeper to a long sleeper during the study period also boosted the risk of stroke by 44% (HR 1.44; 95% 1.12-1.86).
The results “highlight the importance of moderate napping and sleeping duration and maintaining good sleep quality, especially in middle-age and older adults,” Zhang said.
The analysis does not prove cause and effect between long napping or sleeping and stroke; it shows only an association, Zhang added. While the researchers adjusted for age, sex, body mass index, education, and lifestyle and cardiovascular risk factors, they relied on self-reports of napping and sleeping, and did not allow for snoring, sleep apnea, or other sleep disorders. The study involved older, healthy Chinese adults and results may not apply to other groups.
This study was funded by the National Natural Scientific Foundation of China and the National Key Research and Development Program of China.
The authors reported no disclosures relevant to the manuscript.