Stroke doubles dementia risk, concludes large-scale study

Having a stroke significantly increases the risk of dementia, according to the largest study covering 3.2 million people across the world published in the Alzheimer's & Dementia: The Journal of the Alzheimer's Association. People who have had a stroke are around twice as likely to develop dementia. The link between the two persisted even after taking into account other dementia risk factors such as blood pressure, diabetes and cardiovascular disease.

The researchers conducted a meta-analysis and analyzed 36 studies in which participants had a history of stroke, totalling data from 1.9 million people. In addition, they analyzed a further 12 studies that looked at whether participants had a recent stroke over the study period, adding a further 1.3 million people.

Dr. Ilianna Lourida, of the University of Exeter Medical School, said: "We found that a history of stroke increases dementia risk by around 70%, and recent strokes more than doubled the risk. Given how common both stroke and dementia are, this strong link is an important finding. Improvements in stroke prevention and post-stroke care may, therefore, play a key role in dementia prevention."

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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 the episode.

Dr. David Llewellyn, from the University of Exeter Medical School, concluded: "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."

Further research is required to clarify whether factors such as ethnicity and education modify dementia risk following a 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 care and lifestyle can reduce the risk of dementia further.

According to the World Health Organisation,15 million people have a stroke each year. Meanwhile, around 50 million people globally have dementia - a number expected to almost double ever 20 years, reaching 131 million by 2050.