There’s no way to diagnose a stroke before it happens, but researchers say they’ve identified a clue to help doctors predict who’s at risk – the amount of sleep they get at night.
Older adults who said they slept more than eight hours were 46% more likely to suffer strokes in the next decade than adults who slept for six to eight hours, according to an analysis published Wednesday in the journal Neurology. Even worse, the stroke risk for people who went from sleeping less than six hours to sleeping more than eight hours was nearly four times greater than for people who consistently got six to eight hours of ZZZZs.
The findings may help clarify the fuzzy relationship between sleep and stroke. A variety of studies have considered the issue, but the results have been inconsistent.
So researchers from the University of Cambridge and the University of Warwick in England looked for answers in a cancer study. They used data on 9,692 people from Norfolk, England, who participated in the European Prospective Investigation of Cancer. All of them were between the ages of 40 and 79 when they enrolled in the study in the 1990s, and they were tracked for an average of 9.5 years.
Between 1998 and 2000, and again between 2002 and 2004, the study volunteers were asked how many hours they slept at night and whether they tended to sleep well. Researchers also collected a host of demographic and medical information, including their age, education, smoking and drinking habits, body mass index, blood pressure and family history of stroke.
Among the 9,692 volunteers, 346 suffered at least one stroke during the years they were tracked (including 67 strokes that were fatal). But these strokes weren’t evenly distributed among all of the volunteers. After controlling for other factors that might affect stroke risk, they found that “long” sleepers (those who slept more than eight hours a night) were at significantly higher risk than “average” sleepers (those who slept for six to eight hours a night).
People deemed “short” sleepers (those who slept for less than six hours at night) also seemed to be more susceptible to a stroke. Their risk was 18% greater than for average sleepers, but the difference was small enough that it could have been due to chance.
Upon closer inspection, the researchers noticed some intriguing patterns. The relationship between sleep duration and stroke risk was somewhat stronger for women than for men. It was also stronger for strokes that were fatal, according to the study.
When the study participants were examined according to age, the researchers found that sleeping for more than eight hours a night increased stroke risk only for people who were at least 63 years old. On the flip side, they found that sleeping for less than six hours a night heightened stroke risk for younger people more than for older people.
Finally, they discovered that “short” sleepers were more at risk for an ischemic stroke (the kind caused by a clot that blocks blood flow to the brain) while “long” sleepers were more at risk for a hemorrhagic stroke (the kind caused by a ruptured blood vessel bleeds into the brain).
The research team also conducted a meta-analysis that combined their results with those of 11 previously published studies. Altogether, the analysis included nearly 560,000 people from seven countries who suffered a total of more than 8,000 strokes.
In the meta-analysis, “short” sleep was associated with a 15% increased risk of stroke and “long” sleep was linked with a 45% greater risk. Those results validated their findings, the researchers wrote.
Still unclear is whether sleeping too much or too little can actually cause a stroke, or whether the biological processes that lead to a stroke also happen to influence sleep. Other studies have linked long sleep times to cardiac problems like atrial fibrillation, atherosclerosis and other conditions that may make a stroke more likely. But scientists will have to conduct experiments to get a better idea of how sleep and strokes are related, the study authors wrote.
In the meantime, it would behoove doctors to inquire about their patients’ sleep habits – and if their older patients report long sleeping times, they should consider it a warning sign for a stroke, the researchers wrote.
That conclusion was echoed by a neurologist and a sleep researcher in an editorial that accompanied the study.
“Long sleep duration could therefore be a harbinger of stoke through its association with potent cardiovascular risk factors,” wrote Dr. Alberto Ramos of the University of Miami’s Miller School of Medicine and James Gangwisch of Columbia University. “Lengthening sleep duration could portend strokes and serve as an early warning sign, suggesting the need for further diagnostic testing or for taking precautionary measures.”