People who regularly sleep more than 8 hours a day may be at higher risk for having a stroke. The finding is from a 10-year-long prospective study of older people.
The study enrolled more than 9,600 people aged 43 to 81 in 1998 who had never had a stroke. They were asked how much sleep they got then and were asked again 4 years later. Over the course of nearly 10 years, 346 of these people suffered a stroke.
When the researchers accounted for other health issues and behavioral factors, they found that the people who slept more than 8 hours a day were 46% more like to have had a stroke. People who slept less than 6 hours a day were found to have an 18% increase in risk of having a stroke, but this was not statistically significant. The study also found that people who said the amount of sleep they needed had increased were also at higher risk of stroke.
However, the study relies on people reporting how much they slept. Such self reports can be unreliable. The finding is that there is an association between sleeping longer and an increased risk of stroke, not that there is a cause-and-effect relationship between the need for sleep and stroke. One possibility is that some factor that increases the risk of stroke also increases a person's need for sleep.
In addition to the prospective study, the authors also conducted what is called a meta-analysis of several prospective studies of stroke risks, which means that they took the data from those studies and pooled the data together for a statistical analysis. The meta-analysis found a 45% in increase in the risk of stroke for people who got more than 8 hours of sleep per day and a 15% increase in those who got less than 6 hours per day.
The study was conducted by the University of Cambridge and the University of Warwick in the United Kingdom.
The study was published online by the journal Neurology and can be read at: http://www.neurology.org/content/early/2015/02/25/WNL.0000000000001371.full.pdf+html.
