When a person has a stroke, blood flow to the brain is interrupted, and as a result cells die or are damaged — which in many cases can go on to cause dementia. In a scientific statement last year from the American Heart Association and American Stroke Association, scientists estimated that more than half of survivors experience memory and thinking problems in the year that follows, and as many as 1 in 3 will be diagnosed with dementia within five years.
Preliminary research to be presented next week at the International Stroke Conference in Phoenix further supports evidence showing that stroke significantly raises dementia risk.
The study, involving about 180,000 people who suffered a stroke, found that the likelihood of developing dementia was 80 percent greater for people with stroke compared with a matched group from the general population. The risk remained that high even after accounting for other health factors such as high blood pressure, diabetes, and high cholesterol.
“Our results confirm the uniquely high risk of dementia after stroke,” says lead study author Raed Joundi, MD, 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. “The study raises the importance of dementia as a common complication after stroke and that we need to find ways to lower the risk of dementia in this population.”
Dementia Risk Is Greatest Early on But Persists for Years
Dr. Joundi and his team discovered that the chances of developing dementia were highest in the first year after stroke — a nearly threefold increased risk.
“Dementia early after stroke may be due to direct brain injury from the stroke in ‘strategic’ locations that impact cognitive function,” says Joundi.
The analysis noted, however, that the chance of developing dementia post-stroke gradually declines, dropping to a 1.5-times increased risk at five years following a stroke.
“While the risk decreases over time, it remains elevated over the long term,” says Joundi. The findings suggest that survivors should be monitored for cognitive decline soon after having a stroke, and continue to be checked for cognitive decline for years following the event.
How Heart Attack and Type of Stroke Affect Outcomes
Drawing on health databases representing more than 15 million people in the Canadian province of Ontario, Joundi and his collaborators identified 180,940 people with either an ischemic stroke (clot-caused) or intracerebral hemorrhage (bleeding within the brain), per the American Stroke Association. The average participant age was 69, and 55 percent were men.
The team then compared outcomes with two control groups — people in the general population who had not had a heart attack or stroke, and those who’d had a heart attack and not a stroke.
Over an average follow-up of five and a half years, dementia occurred in nearly 1 in 5 stroke survivors.
People who’d had only a stroke, though, had about the same risk of developing dementia as the general population.
For Victor W. Henderson, MD, director of the Alzheimer’s Disease Research Center at Stanford University in California, that result corresponds with research he’s done indicating that the risk of Alzheimer disease and other dementias was not higher in patients with heart attack.
“People who have a heart attack have vascular risk factors, but they are not necessarily going to affect the brain in a way that is going to lead to dementia,” says Dr. Henderson, who was not involved in this study.
The latest study also highlighted that intracerebral hemorrhage, or bleeding in the brain, increased the risk of dementia even further. Those with this type of stroke had about a 150 percent higher likelihood of dementia compared with the general population.
Earlier research has found that the buildup of amyloid plaques in blood vessels, which is associated with Alzheimer’s disease, is likely to raise the risk of this type of stroke.“Intracerebral hemorrhages aren’t as common ischemic strokes, but they’re often much more serious and damaging,” says Henderson.
In addition, the new analysis underscored that recurrent strokes further heighten dementia risk — but dementia diagnosis was more common than having another stroke.
“This was surprising and means we need to pay attention to dementia as a complication of stroke in the short and long-term,” says Joundi.
Taking Action to Lower Stroke Risk
The latest numbers from American Heart Association’s Heart Disease and Stroke Statistics 2024 Update show that about 795,000 people experience a new or recurrent stroke every year. Approximately 610,000 of these are first attacks, and 185,000 are recurrent attacks.
Stroke can produce a range of disabilities that impact day-to-day functioning, including impaired speech, limited physical abilities, and weakness or paralysis of limbs. Adding dementia risk to that list provides even more reason to take steps to reduce the possibility of having a stroke.
“Taking heed of your cardiovascular health is something you can act on,” says Henderson.
To reduce stroke risk, the Centers for Disease Control and Prevention (CDC) encourages lifestyle changes, such as increasing physical activity, eating a healthy diet, smoking cessation, keeping a healthy weight, and limiting alcohol consumption.
The CDC also recommends working with a doctor to control diabetes, blood pressure, and cholesterol.
“Almost one-fifth of people develop dementia after stroke, primarily in the first few years,” says Joundi. “This is a significant issue given the number of people having stroke is increasing with time due to the aging populations worldwide. There is a major need to develop novel strategies to prevent dementia after stroke.”