Sleeping nine or more hours a night may increase someone’s risk of stroke, a new study suggests.

According to the research, people who sleep and nap too long may increase their risk for stroke by 85%. Regular 90-minute midday naps can raise the risk 25%, compared with not napping or napping for only 30 minutes.

“People, especially middle-aged and older adults, should pay more attention to their time spent in bed attempting to sleep and midday napping, and sleep quality, because appropriate duration of sleep and nap, and maintaining good sleep quality may complement other behavioral interventions for preventing stroke,” said researcher Dr. Xiaomin Zhang. She is a professor in the Department of Occupational and Environmental Health at Huazhong University of Science and Technology in Wuhan, China.

Zhang cautioned that these findings don’t prove long napping and sleeping cause stroke, only that there is an association.