Sleeping for more than the recommended eight hours increases the risk of stroke and this risk doubles for older people who do it persistently. According to a study by the University of Cambridge, the risk is four times higher also for people who sleep less than six hours.
Researchers from Cambridge followed just under 10,000 people aged 42 to 81 years old during 1998-2000 and then again four years later. Almost seven out of ten participants reported sleeping between six and eight hours a day, whilst one in ten reported sleeping for over eight hours a day. Participants who slept for less than six hours or more than eight hours were more likely to be older, women and less active, show the findings.
Over the almost ten year period of the study, 346 participants suffered a stroke, either non-fatal or fatal stroke and researchers say that that people who slept longer than eight hours a day were at a 46% greater risk of stroke than average. Also, those who slept less than six hours a day were at an 18% increased risk, but the small number of people falling in this category meant the association was not statistically significant.
The risk was even greater for those whose reported sleep increased from short to long over the four years – their risk was close to four times that of people who maintained an average sleep duration.
“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,” says Yue Leng, PhD candidate at the University of Cambridge.
Researchers note that it is still unclear why there’s a link between sleep and stroke risk. Previous studies have already linked the lack of sleep 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 new study suggests that the association between longer sleep duration and higher risk of stroke was independent of normal risk factors for cardiovascular disease.