People who have had a stroke are twice as likely to develop dementia, according to a new study.

Researchers from the University of Exeter Medical School led the study, which analyzed 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, according to the researchers.

The study builds on previous research that established a link between stroke and dementia, although that research had not quantified the degree to which stroke actually increased dementia risk.

To better understand the link between the two, researchers analyzed 36 studies where participants had a history of stroke, totaling 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.

The new research, published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, is the first meta-analysis in the area, the researchers note.

“We found that a history of stroke increases dementia risk by around 70 percent, and recent strokes more than doubled the risk,” said Dr. Ilianna Lourida of the University of Exeter Medical School.

“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.”

According to the World Health Organization, 15 million people have a stroke each year. Meanwhile, around 50 million people globally have dementia, a number expected to almost double over the next 20 years, reaching 131 million by 2050, the researchers report.

Stroke characteristics, such as the location and extent of brain damage, may help explain the variation in dementia risk observed between studies, the researchers noted. They added there was some suggestion that dementia risk may be higher for men following a stroke.

Further research is required to clarify whether factors such as ethnicity and education modify dementia risk following a stroke, the researchers said.

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, the researchers 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,” concluded Dr. 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.”

Source: University of Exeter