A new study out of China appears to show that lots of sleep has been associated with an increased risk of having a stroke. The study, conducted by Xiaomin Zhang, MD, PhD, of Huazhong University of Science and Technology in Wuhan, China, and colleagues, was funded by the National Natural Scientific Foundation of China and the National Key Research and Development Program of China. The findings have been published in Neurology, the medical journal of the American Academy of Neurology.
Zhang and colleagues collected data from 31,750 retired employees of the Dongfeng Motor Corporation in China for their study. Participants had an average baseline age of about 62 and no history of coronary heart disease, cancer, or stroke. Each participant completed a questionnaire that outlined their usual sleeping and napping patterns and allowed them to rate their sleep quality. Eight percent reported taking naps lasting more than 90 minutes and 24 percent said they slept nine or more hours per night.
Study participants were followed for an average of six years, during which time there were 1,557 stroke cases. Those sleeping at least nine hours overnight were 23 percent more likely to have a stroke in that time period than those sleeping seven or eight hours. A 90-minute nap was linked to a 25 percent greater chance of having a stroke.
People who were both long nappers and long sleepers were 85 percent more likely to have a stroke than people who were moderate sleepers and nappers. People who were long sleepers and had poor sleep quality had an 82 percent increased stroke risk over moderate sleepers with good sleep quality. These numbers held even after the researchers adjusted for age, sex, body mass index, education, and lifestyle and cardiovascular risk factors.
The analysis does not prove cause and effect between long napping or sleeping and stroke; it shows only an association. There may be numerous other factors at play, like maybe those who tended to sleep more did so because of health problems. More research is needed before a definitive answer can be found.