By Robert Preidt
In what they say is the largest analysis of its kind, British researchers examined 48 studies that included 3.2 million people worldwide.
"We found that a history of stroke increases dementia risk by around 70 percent, and recent strokes more than doubled the risk," said researcher Ilianna Lourida, from the University of Exeter Medical School.
"Given how common both stroke and dementia are, this strong link is an important finding," Lourida added in a university news release. "Improvements in stroke prevention and post-stroke care may therefore play a key role in dementia prevention."
The association between stroke and increased dementia risk remained even after other dementia risk factors such as blood pressure, diabetes and heart disease were taken into account, the researchers said.
Though the study did not prove that strokes cause dementia, this is the strongest evidence to date of a link between the two, according to the researchers.
Researcher David Llewellyn, also from the University of Exeter, said, "Around a third of dementia cases are thought to be potentially preventable, though this estimate does not take into account the risk associated with stroke.
"Our findings indicate that this figure could be even higher, and reinforce the importance of protecting the blood supply to the brain when attempting to reduce the global burden of dementia," he said.
More study is needed to find out if factors such as ethnicity and education influence dementia risk following stroke, the study authors added. In the latest review, there was some suggestion that the risk might be higher for men.
The investigators also noted that most stroke survivors do not develop dementia, so further research is needed to determine whether differences in post-stroke care and lifestyle can reduce the risk of dementia.
About 15 million people worldwide have a stroke each year, according to the World Health Organization. About 50 million people worldwide have dementia, and that's expected to almost double every 20 years, reaching 131 million by 2050.
The findings were published Aug. 31 in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.