Having a stroke may triple a person's risk for developing dementia within the following year, new research finds.

And while that risk begins to drop after the first 12 months, it remains elevated for up to 20 years, according to findings to be presented next week at the American Stroke Association's International Stroke Conference in Phoenix. The research is considered preliminary until full results are published in a peer-reviewed journal.

"Our findings show that stroke survivors are uniquely susceptible to dementia," lead researcher Dr. RaedvJoundi said in a news release. Joundi is an assistant professor at McMaster University in Hamilton, Ontario, Canada, and an investigator at the Population Health Research Institute, a joint institute of McMaster University and Hamilton Health Sciences.

Roughly 610,000 people experience a first stroke each year, while 185,000 more have recurrent strokes, according to the American Heart Association. The Centers for Disease Control and Prevention estimates roughly 7 million people 65 and older in the U.S. had dementia in 2014, which could increase to nearly 14 million by 2060.

To determine post-stroke dementia risk, researchers analyzed data from hospital admissions, emergency department visits and pharmacies prescribing medications for dementia across Ontario. They identified 180,940 people who recently had either an ischemic stroke, caused by a blood clot, or one caused by bleeding in the brain, called an intracerebral hemorrhage. They matched the survivors to two control groups – people in the general population who had neither a heart attack nor a stroke, and those who had had a heart attack but not a stroke. They tracked new cases of dementia in all groups for up to 20 years.

Over an average follow-up of almost six years, nearly 19% of people who had strokes developed dementia. Compared to the general population, dementia risk was 80% higher among those who had a stroke, with the risk jumping to nearly 150% higher in those who had a bleeding stroke. Risk was nearly 80% higher in stroke survivors compared to heart attack survivors.

The risk of developing dementia was highest in the year immediately following a stroke. During the first 12 months, stroke survivors faced a nearly threefold increased risk for dementia, compared to their peers who did not have strokes. By five years after the stroke, that risk dropped to 1.5 times. The risk continued to decline over 20 years of follow-up but remained higher for people who had strokes than for those who had not.

The study showed people who had strokes faced a higher risk for dementia than they did for a subsequent stroke, Joudi said.

"Stroke injures the brain, including areas critical for cognitive function, which can impact day-to-day functioning," he said. "Some people go on to have a recurrent stroke, which increases the risk of dementia even further, and others may experience a progressive cognitive decline similar to a neurodegenerative condition."

A 2023 report from the AHA encourages screening stroke survivors for signs of cognitive decline and collaborative care from an interdisciplinary team to provide support to those who show the signs.
Joundi said the study shows there is a large burden of post-stroke dementia in Canada and called for more research to clarify why some stroke survivors develop dementia and others do not.

The findings, he said, "reinforce the importance of monitoring people with stroke for cognitive decline, instituting appropriate treatments to address vascular risk factors and prevent recurrent stroke, and encouraging lifestyle changes, such as smoking cessation and increased physical activity, which have many benefits and may reduce the risk of dementia."