Too much sleep raises stroke risk - study

Previous studies have suggested a possible link between sleep and the risk of stroke. Photo / 123RF

Getting too much sleep may increase the risk of having a stroke, scientists say.

According to the study by the University of Cambridge, this risk doubles for older people who persistently sleep longer than the average of eight hours a night.

For those whose sleep patterns increased from short to long over time, the risk was close to four times that of people who maintained an average sleep pattern.

Yue Leng, from the university, said: "It's apparent both from our own participants and the wealth of international data that there's a link between sleeping longer than average and a greater risk of stroke.

"What is far less clear, however, is the direction of this link, whether longer sleep is a symptom, an early marker or a cause of cardiovascular problems."

Previous studies have suggested a possible link between sleep and the risk of stroke.

But the new research is the first to provide detailed information about the British public and to examine the relationship between a change in sleep duration and stroke risk.

Researchers from the university's Department of Public Health followed almost 10,000 people aged 42 to 81 over almost 10 years.

Most reported sleeping between six and eight hours a day while one in 10 reported sleeping for more than eight hours a day.

Over the course of the study, 346 participants suffered a stroke and, after taking into account other factors, the team concluded that people who slept longer than eight hours a day were at 46 per cent greater risk of stroke than average.

The risk doubled for those whose reported persistently long sleep over the entire course of the study.

The researchers say it is so far unclear why the link between sleep and stroke risk exists

Lack of sleep has been linked with factors such as disrupted metabolism and raised levels of the "stress hormone" cortisol, all of which may lead to higher blood pressure and increased stroke risk.

But the findings suggest that the link was independent of normal risk factors for cardiovascular disease.

Senior author Kay-Tee Khaw said: "We need to understand the reasons behind the link between sleep and stroke risk.

"What is happening in the body that causes this link? With further research, we may find that excessive sleep proves to be an early indicator of increased stroke risk, particularly among older people."

The study was supported by the Medical Research Council and Cancer Research UK.

- AAP