Do you sleep a lot, putting in a lot of hours under the covers? Then you might be increasing your risk of stroke, a study suggests.

Older adults who reported sleeping more than 8 hours each night were 46 percent more likely to suffer a stroke in the next decade than those who got only 6 to 8 hours of sleep each night, British researchers say.

They caution that although their study, published in the journal Neurology, found an association between longer sleep hours and stroke, they can't yet be sure whether it's a cause, a consequence or an early warning signal of declining brain health.

"Previous studies have already suggested a possible association between sleep and risk of stroke," says lead researcher Yue Leng from the University of Cambridge.

However, results of those previous studies have been inconsistent, so researchers at Cambridge and the University of Warwick looked for new data in a study originally investigating cancer.

As part of that study, the European Prospective Investigation of Cancer, 9,692 people in England between the ages of 40 and 79 were tracked for almost 10 years.

Among that data gathered in that tracking was information on their sleep habits, including the number of hours of sleep they got each night on average.

Of the 9,692 participants, 346 suffered a stroke during the study period, but those strokes weren't evenly distributed among the group, the Cambridge and Warwick researchers found.

"Long" sleepers, those getting more than 8 hours of sleep nightly, were at significantly higher risk than "average" sleepers who averages 6 to 8 hours, they discovered.

An even more significant finding, researchers said, was that people who had a change in their sleep habits -- going from sleeping less than 6 hours to an excess of 8 hours nightly -- had a risk of stroke four times that of people whose average sleep hours were always consistent.

Dr. Alberto Ramos, a neurology professor at the University of Miami Miller School of Medicine who authored an editorial to accompany the published study, says he suspects that long sleeping times are a warning signal but "the change in sleeping patterns is more the concern."

Adults over the age of 60 who find they've begun sleeping more should take steps to ensure their cardiovascular risk factors such as cholesterol and blood pressure are under control, he added.

For his part, Leng says much more research is needed and the study findings should not be taken as reason to cut sleep hours to reduce stroke risk, because adequate sleep is vital to continued good health.