By Lisa Rapaport

(Reuters Health) – People who have recently experienced a stroke may be more than twice as likely to develop dementia than individuals who haven’t had a stroke, a new study suggests.

While stroke has long been linked to a heightened risk of dementia, particularly in older adults, the exact magnitude of the increased risk hasn’t been consistent across previous studies investigating this connection. For the current study, researchers pooled data from 48 previous studies with a total of 3.2 million participants worldwide.

People who had a recent stroke were 2.2 times more likely to develop dementia than people who never had a stroke, the analysis found. And a history of stroke was associated with a 69 percent higher chance of developing dementia.

“These findings stress the importance of protecting the blood supply to the brain in order to protect against dementia,” said senior study author Dr. David Llewellyn of the University of Exeter Medical School in the UK.

“By focusing upon lifestyle factors that are within our control we can reduce our risk of developing dementia as a result of stroke,” Llewellyn said by email.

“Quit smoking, eat a Mediterranean diet, get physically and mentally active, and drink less alcohol,” Llewellyn advised. “Most people who have a stroke do not develop dementia as a result, so improvements in lifestyle after stroke are also likely to be beneficial.”

Alzheimer’s disease is the most common cause of dementia among older adults. The progressive brain disorder slowly erodes memory and thinking skills and eventually leaves people unable to handle basic tasks in daily life.

Previous research has linked so-called vascular risk factors, including obesity, diabetes, smoking, high cholesterol and elevated blood pressure, to higher odds of dementia, cognitive decline and Alzheimer’s disease.

But it’s been unclear whether these factors contribute indirectly by restricting blood flow in the brain, or if they directly cause a buildup of amyloid protein fragments that are linked to Alzheimer’s.

Certain characteristics of stroke, such as the location and the extent of brain damage, may also influence the risk of dementia, the study authors conclude. Men may also have a greater risk of dementia after a stroke than women.

One limitation of the analysis is that the smaller studies varied in design, duration, and how they assessed stroke and dementia, researchers note in Alzheimer’s & Dementia.

Still, the results add to a large body of evidence linking stroke to dementia, said Dr. Andrew Budson, a researcher at the Veterans Affairs Boston Healthcare System and Boston University School of Medicine who wasn’t involved in the study.

“Although not surprising, this important review emphasizes one way that people can reduce their chances of developing dementia,” said Budson, author of “Seven Steps to Managing Your Memory: What’s Normal, What’s Not, and What to Do About It.”

“The take home message,” he advised in an email, “is that you will be less likely to develop dementia if you reduce your risk of stroke by quitting if you smoke, keeping your sugars under control if you have diabetes, taking medications for high blood pressure and cholesterol as prescribed, losing weight if you are obese or overweight, eating a Mediterranean style diet, and engaging in aerobic exercise.”

SOURCE: Alzheimer’s & Dementia, online August 31, 2018.