New evidence from the Centre for Healthy Brain Ageing (CHeBA) indicates that older adults who experience a stroke for the first time will have substantial immediate and accelerated long-term-cognitive decline.

Stroke is a leading cause of disability and dementia globally, with projections indicating a continued rise in both prevalence and burden. The new research, published today in JAMA Network Open, looked at finding out exactly how a stroke impacts a person's cognitive abilities.

Stroke occurs when blood flow to part of the brain is blocked or reduced, causing damage to brain cells. Previous research from the Centre has shown that more than a third of stroke survivors' ability to think, remember and make decisions is significantly disadvantaged after stroke, with clear deficits in cognition or vascular dementia present.

Vascular dementia, the second most common type of dementia, is caused by reduced blood flow to the brain. The research, led by biostatistician and Research Associate Jess Lo, addressed many unanswered questions about this dementia type, which is yet to be studied as extensively as Alzheimer's disease.

"Although we do experience changes to our brain functioning over time and as we age, certain medical conditions can potentially speed up these changes, which may lead to cognitive impairment or dementia," said Lo.

"We wanted to understand exactly how stroke affects cognitive abilities such as thinking, memory and decision-making, and what the impacts are both short and long term."

The research analyzed data from 14 studies that followed community-dwelling older adults without a history of stroke or dementia, with an average age of 73 over many years, tracking their health and cognitive abilities. The studies, part of the CHeBA-led international Cohort Studies of Memory in an International Consortium (COSMIC), span 11 countries including Australia, Brazil, France and the US.

With data from 20,860 participants, the researchers identified people who experienced their first stroke during the study period.

"By analyzing their cognitive abilities over several assessment time points before and after stroke, we mapped out the course of changes in their thinking and memory over the periods before and after stroke, and therefore, were able to determine the changes in cognitive ability due to a stroke," said Lo.

The research observed a moderate rate of cognitive decline in all individuals before any stroke, which may be related to aging and health conditions typical of someone around 73 years old. However, the research also revealed that for older adults experiencing a stroke there was an associated significant immediate drop in cognitive ability in all areas of cognitive performance, followed by a gradual long-term decline.

"After a stroke, the rate of decline accelerated slightly compared to the rate before the stroke. Areas of cognitive performance affected included language, processing speed, and executive function," said Lo.

The research also found that individuals who had a history of diabetes, hypertension, high cholesterol, cardiovascular disease, depression, smoked or were APOE4 carriers exhibited significantly faster cognitive decline before any stroke.

"This supports the hypothesis that vascular risk factors exert their greatest impact on cognitive function years before stroke onset," said Lo. "Targeting modifiable risk factors at an early stage may reduce the risk of stroke but also the subsequent risk of stroke-related cognitive decline and cognitive impairment."

Senior author on the paper and Co-Director of the CHeBA, Professor Perminder Sachdev, said that this global collaborative study highlights the significant and lasting negative impact of stroke on brain cognition.

"Our findings can help clinicians better plan for the ongoing needs of stroke survivors who are at risk of disability and a lower quality of life," said Sachdev.