Lack of sleep has moved to the forefront of public health issues due to its association with major complications, including obesity, diabetes, and heart disease. With health experts urging every person of every age to get more sleep, we tend to ignore the question: How much sleep is too much sleep? A recent study conducted at the Department of Public Health and Primary Care at the University of Cambridge has found that sleeping for more than eight hours a day can significantly increase our risk for a stroke.

"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," Yue Leng, PhD candidate at the University of Cambridge, said in a statement. "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."

Leng and his colleagues used the European Prospective Investigation into Cancer (EPIC)-Norfolk cohort to follow close to 10,000 people between the ages of 42 and 81 over a time span of 9.5 years. Researchers asked each participant, on average, how many hours they slept in a day and if they slept well at the beginning of the study and again four years later. By the end of close to 10 years of follow-up, 346 participants has suffered either a fatal or nonfatal stroke.

Only 10 percent of participants reported sleeping more than eight hours a day compared to 70 percent of participants who reported sleeping between six and eight hours a day. People who slept longer than eight hours a day were at a 46 percent higher risk for stroke compared to normal, while people who slept less than six hours a day were at an 18 percent higher stroke risk. Sleeping for more than eight hours a day on a consistent basis doubled the risk of stroke compared to sleeping between six and eight hours.

"We need to understand the reasons behind the link between sleep and stroke risk," senior author on the study, Professor Kay-Tee Khaw, said in a statement. "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 research team recognized that lack of sleep is regularly associated with disrupted metabolism and higher levels of cortisol, also known as the “stress hormone,” which can lead to higher blood pressure and increase stroke risk. As to how longer sleep duration can lead to a higher stroke risk, independent of other normal risk factors for heart disease, Khaw said more research is needed to substantiate any potential link between sleep and stroke risk.

A conflicting study presented at the SLEEP 2012 conference in Boston found that people who sleep less than six hours a night are four times more likely to suffer a stroke. This increased risk for a stroke applies to healthy adults who have no detectable risk factors or family history of a stroke. Researchers from the University of Alabama in Birmingham said that insufficient sleep may be a precursor that can lead to more severe risk factors associated with a stroke.

Source: Neurology. 2015.