By tracking changes in sleep habits, older adults or their caretakers may be tipped off to an impending stroke. Researchers have found that older adults who sleep for longer than eight hours each night are at a 46 percent greater risk of stroke, according to a new study published in Neurology on Wednesday.    

“I think physicians and patients should be alerted and cognizant of their sleep patterns, particularly the elderly, which seem to be the most vulnerable population,” Alberto Ramos, a neurologist at University of Miami who wrote an editorial about the study, said. “I think that by a single question, ‘How many hours do you sleep per night?', the physician may potentially obtain a wealth of information about the patient's health and act upon it.”

Older adults who suddenly start sleeping longer hours are at an even greater risk than those who have always slept a lot, according to the study. “People who shifted over time from sleeping less than six hours a night to sleeping more than eight hours a night were nearly four times more likely to have a stroke than people who consistently slept an average amount,” said Yue Leng, a co-author and postdoctoral researcher from University of Cambridge.

While it’s possible that sleeping for a long time is somehow causing people to have more strokes, Leng says it’s more likely that people who sleep for long periods also harbor some sort of complication which boosts their risk of stroke, such as sleep apnea. Nevertheless, Leng thinks her results may have the potential to warn patients and their physicians of a possible stroke. "It is worth noting excessive sleep as an early sign of increased stroke risk, particularly among older people,” she writes with her colleagues in the study’s conclusion.

For her analysis, Leng mined a dataset of 9,262 European adults between the ages of 42 to 81 years old. The participants recorded their sleep patterns during two-year periods from 1998-2000 and 2002-2004, and then reported back about whether or not they’d suffered a stroke up until 2009.

She divided participants into groups by the number of hours they tended to sleep at night based on their surveys and dubbed those who tended to get more than eight hours of sleep a night “long sleepers.” These people made up about 10 percent of the population she studied. At the same time, she also reviewed studies which were previously published on the relationship between the risk of stroke and hours of sleep, and found that those results reinforced her findings.   

“The National Sleep Foundation, Centers for Disease Control and National Institutes of Health are all noting that sleep is an important issue related to public health,” said Jing Fang, an epidemiologist in CDC’s Division of Heart Disease and Stroke Prevention who published a study last year which detected a similar relationship between stroke and sleep. “They've related it to chronic disease and they have a recommendation for the amount of appropriate sleep – which is eight hours.”

Though scientists have suggested a sleep-stroke link in the past, Leng’s work shows that the boost in stroke risk occurs regardless of whether people are already predisposed to cardiovascular disease due to high blood pressure or high cholesterol. Leng’s study also links different types of stroke with duration of sleep – for example, she found that the risk of ischemic stroke seems to be associated with shorter sleep cycles while the heightened risk of hemorrhagic stroke comes with longer sleep, which may provide clues to researchers who further examine this connection in the future.

Patrick Lyden, director of the stroke program at Cedars-Sinai Medical Center in Los Angeles, emphasizes that more work needs to be done to figure out whether the risk of stroke is dependent on sleep or due to some other cause, and does not think Leng’s results are robust enough for physicians to consider long hours of sleep to be an indicator for stroke. Even so, he said, “All things in moderation, including sleep.”