People who sleep for more than eight hours a day have an increased risk of stroke, according to a study by the University of Cambridge, and this risk doubles for older people who persistently sleep longer than average. However, the researchers say it is unclear why this association exists and call for further research to explore the link.
Previous studies have already suggested a possible association between sleep and risk of stroke, but today’s study, published in the journal Neurology, is the first to provide detailed information about the British population and to examine the relationship between a change in sleep duration over time and subsequent stroke risk.
Researchers from the Department of Public Health and Primary Care at the University of Cambridge followed just under 10,000 people aged 42-81 years of age from the European Prospective Investigation into Cancer (EPIC)–Norfolk cohort over 9.5 years. During 1998-2000 and then again four years later, they asked the cohort how many hours on average they slept in a day and whether they generally slept well.
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.
Over the almost ten year period of the study, 346 participants suffered a stroke, either non-fatal or fatal stroke. After adjusting for various factors including age and sex, the researchers found that people who slept longer than eight hours a day were at a 46% greater risk of stroke than average.
People 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.