Too much sleep may raise the risk of stroke, research suggests.
Scientists from Huazhong University of Science and Technology in Wuhan, China, asked more than 31,000 people how much shut eye they got a day.
Perhaps surprisingly, those who slept for more than nine hours were nearly a quarter (23%) more likely to suffer a stroke over the next six years.
When napping was added to the mix, the risk went up to 85%, the results show.
“Previous studies have shown long nappers and sleepers have unfavorable changes in their cholesterol levels and increased waist circumferences, both of which are risk factors for stroke”, study author Dr Xiaomin Zhang said.
“In addition, long napping and sleeping may suggest an overall inactive lifestyle, which is also related to increased risk of stroke.”
The Sleep Council recommends adults get between seven and nine hours of shut eye a night.
During this time, the body replenishes its energy stores and repairs any damage, while the mind organises and stores memories from the day before.
Too much sleep, however, has been linked to weight gain, diabetes and even a premature death.
To learn more about how slumbering affects our health, the scientists looked at thousands of healthy adults, with an average age of 62.
The participants were asked about their sleep and napping habits. A midday nap is reportedly common in China, with 8% of those in the study nodding off for more than an hour-and-a-half a day.
Nearly a quarter (24%) claimed to get at least nine hours kip a night. Compared to those who got less, these individuals were significantly more likely to suffer a stroke down the line.
The risk was higher still when a long night’s sleep was combined with a lengthy nap, results - published in the journal Neurology - show.
Napping for 90 minutes alone increased the odds of a stroke by 25% compared to a kip of half-an-hour or less.
When it came to sleep quality, those who rated it as poor were up to 56% more likely to suffer a stroke than those who slumbered well.
Kipping for more than nine hours a night, but poorly, raised the risk by 82%.
“These results highlight the importance of moderate napping and sleeping duration and maintaining good sleep quality, especially in middle-age and older adults,” Dr Zhang said.
Exactly why this occurs is unclear. Some believe too much sleep triggers inflammation, or could indicate depression or “low socioeconomic status”.
Needing a lot of shut eye also suggests “an epiphenomenon of comorbidities”, the scientists wrote.
The scientists stress the information was taken from a questionnaire, rather than being monitored in a trial.
Different results may also occur among less healthy or non-Chinese adults, they add.