People who sleep nine or more hours per night are 23 per cent more likely to later have a stroke than people who sleep seven to less than eight hours per night, warns a new study.

The results revealed that long naps are also not good for your health. People who took a regular midday nap lasting more than 90 minutes were 25 per cent more likely to later have a stroke than people who took a regular nap lasting from one to 30 minutes, said the study published online in Neurology, the medical journal of the American Academy of Neurology. People who took no naps or took naps lasting from 31 minutes to one hour were no more likely to have a stroke than people who took naps lasting from one to 30 minutes.

"More research is needed to understand how taking long naps and sleeping longer hours at night may be tied to an increased risk of stroke, but previous studies have shown that long nappers and sleepers have unfavourable changes in their cholesterol levels and increased waist circumferences, both of which are risk factors for stroke," said study author Xiaomin Zhang of Huazhong University of Science and Technology in Wuhan, China. "In addition, long napping and sleeping may suggest an overall inactive lifestyle, which is also related to increased risk of stroke," Zhang said.

The study involved 31,750 people in China with an average age of 62. The people did not have any history of stroke or other major health problems at the start of the study. They were followed for an average of six years. During that time, there were 1,557 stroke cases. The people were asked questions about their sleep and napping habits. People who were both long nappers and long sleepers were 85 per cent more likely to later have a stroke than people who were moderate sleepers and nappers, said the study.

"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.