People who have suffered a stroke are 70 per cent more likely to develop dementia, a new study has revealed.

Around a third of dementia cases are thought to be potentially preventable. However, this estimate does not take into account the risk associated with stroke.

Stroke characteristics such as the location and extent of brain damage might help to explain the variation in dementia risk.

The study reinforces the importance of protecting the blood supply to the brain when attempting to reduce the global burden of dementia, the researchers explained.

"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 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," she added.

For the study, published in the journal Alzheimer's & Dementia: The Journal of the Alzheimer's Association, the team analysed 36 studies where participants had a history of stroke, totalling data from 1.9 million people. 

In addition, they analysed 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 research found that the link between stroke and dementia persisted even after taking into account other dementia factors such as blood pressure, diabetes and cardiovascular diseases.

Some studies also suggested that dementia risk might be higher for men following a stroke.

According to the World Health Organisation (WHO), 15 million people have a stroke each year. 

Meanwhile, around 50 million people globally have dementia -- a number expected to more than double over 20 years, reaching 131 million by 2050, it said.