Some of the non-dementia memory loss experienced by older individuals may be due to “silent strokes,” new research suggests.
Such strokes typically produce no noticeable symptoms when they’re occurring. But they leave behind tiny pockets of dead cells in the brain, which can be picked up by high-resolution brain scans.
The study, which was led by researchers at New York’s Columbia University and published Tuesday in the journal Neurology, found only an association between silent strokes and memory problems, not a direct causal link. Still, the findings are interesting, particularly since they also suggest that silent strokes can contribute to memory difficulties even if there is no accompanying shrinkage of the hippocampus, an area of the brain believed to play a key role in memory.
The findings also offer yet another reason for why we need to become more aggressive about stroke prevention.
The study‘s details
For the study, researchers recruited 658 people aged 65 and older. None had dementia, and most had no previous clinical history of stroke. All were given magnetic resonance imaging (MRI) brain scans, and one in four were found to have experienced previous silent strokes. (That’s less than the one-in-three with silent strokes that other researchers have found among that age group, according to background information in this study.)
All the study’s participants also underwent tests that measured their memory as well as their skill at cognitive tasks involving language, visual perception and information processing. An analysis of the results found that those in the silent-stroke group scored somewhat worse on these tests than the people who were stroke-free.
Interestingly, the size of the participants’ hippocampus didn’t matter. Previous studies have attributed a smaller hippocampus to age-related memory decline, but this study found that a smaller hippocampus and evidence of past silent strokes were independently associated with poorer memory skills.
These findings, therefore, support the idea that silent strokes have a negative effect on memory even in the absence of other biological markers (like a smaller hippocampus). The findings also point to “a critical need for stroke prevention,” say the study’s authors.
Strokes — including the silent types — “are a largely preventable brain injury, with clearly identified risk factors, and prevention programs,” the study’s authors conclude. “A public health push toward emphasizing stroke prevention may significantly decrease incidence of dementia.”
Minnesota is doing better than most states when it comes to strokes. We have one of the lowest stroke death rates in the nation — a rate that has been declining at a faster pace than the country as a whole.
But in 2010, the latest year that statistics are available, that death rate took a slight tick upward, from 34.1 to 35.8 per 100,000 Minnesotans, according to James Peacock, an epidemiologist at the Minnesota Department of Health (MDH).
“One year doesn’t make a trend, and we have seen very strong declines in both heart disease and stroke mortality for several decades,” Peacock noted in an e-mail. “Despite this, it is important to note that risk factors for stroke are not improving substantially, especially blood pressure. As baby boomers get older and start turning 65 in greater numbers, an even larger population will be at risk for stroke in the coming years.”
To find out how Minnesota is doing on stroke prevention, I called Stanton Shanedling, supervisor of the MDH’s heart disease and stroke prevention unit.
The state released a new stroke (and heart disease) prevention plan last year, he told me. The plan’s strategies and tactics focus, of course, on reducing stroke’s risk factors, which include the usual suspects: obesity, smoking, high blood pressure, a poor cholesterol profile and physical inactivity.
“Unless we start addressing those risk factors, we’re going to start seeing a higher incidence, and in younger populations, which is kind of disturbing,” said Shanedling.
“We’re seeing more kids who are diabetic,” he pointed out, “and having diabetes is in itself a risk factor for stroke.”
A hard nut to crack
Another major part of Minnesota’s stroke prevention plan is to make all of us more aware of the most common signs and symptoms of stroke (slurred speech; blurred vision; numbness or muscle weakness of the face, arm or leg; trouble standing or walking; a sudden, severe and unexplainable headache), so that we’ll seek medical care quickly. Research has shown that individuals who receive treatment within three hours of experiencing a stroke are less likely to experience long-term disability. (In 2009, a survey found that only half of Minnesotans could identify all five major signs of stroke and correctly indicate that those signs meant a 9-1-1 call was needed.)
But this latest study was about silent strokes, which, by their very definition, don’t have any outward signs. “They are, frankly, a hard nut to crack,” acknowledged Shanedling.
All the more reason that we need to work on reducing our risk. You’ll find detailed information about stroke prevention at the websites of the Minnesota Department of Health, the National Stroke Association and the National Institute of Neurological Disorders and Stroke.