People who have had a stroke are around twice as likely to develop dementia, according to a large-scale study.
Researchers at the University of Exeter in the UK analysed data on stroke and dementia risk from 3.2 million people across the world.
The link between stroke and dementia persisted even after taking into account other dementia risk factors such as blood pressure, diabetes and cardiovascular disease.
The findings, published in the journal Alzheimer's & Dementia, give the strongest evidence to date that having a stroke significantly increases the risk of dementia.
"We found that a history of stroke increases dementia risk by around 70 per cent, and recent strokes more than doubled the risk," said Ilianna Lourida of the University of Exeter.
"Given how common both stroke and dementia are, this strong link is an important finding," said Lourida.
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"Improvements in stroke prevention and post-stroke care may therefore play a key role in dementia prevention," she said.
According to the World Health Organisation (WHO), 15 million people have a stroke each year.
Around 50 million people globally have dementia - a number expected to almost double over 20 years, reaching 131 million by 2050, researchers said.
Stroke characteristics such as the location and extent of brain damage may help to explain variation in dementia risk observed between studies, and there was some suggestion that dementia risk may be higher for men following stroke, they said.
Further research is required to clarify whether factors such as ethnicity and education modify dementia risk following stroke.
Most people who have a stroke do not go on to develop dementia, so further research is also needed to establish whether differences in post-stroke care and lifestyle can reduce the risk of dementia further, according to researchers.
"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," said David Llewellyn, from the University of Exeter Medical School.
"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," Llewellyn said.