Symptomless, unnoticed strokes more than double the risk of developing Alzheimer's disease, according to a large Dutch study that suggests many people could prevent the mind-robbing disorder by keeping their heart and blood vessels healthy.
Elderly people who suffered tiny "silent strokes" -- detected by an MRI -- had their mental function decline more sharply and were about 2.3 times more likely to develop Alzheimer's or other types of dementia, researchers at Erasmus Medical Center found.
The study, the first major one on silent strokes, was published in today's New England Journal of Medicine. Experts say it indicates middle-aged people should exercise, eat a balanced diet and quit smoking to lower their weight, blood pressure, cholesterol and blood sugar level.
The work provides "very powerful confirmation" of evidence linking narrowed blood vessels in the brain, stroke and Alzheimer's, said Bill Thies, vice president for medical and scientific affairs at the Alzheimer's Assn.
"This is an extraordinarily well-done study in a big group of people," Thies said. "They have identified an outcome from these small (strokes) that we wouldn't have suspected."
Silent strokes are fairly common in the elderly, based on MRI scans of the 1,015 people aged 60 to 90 in the study, said lead investigator Dr. Monique Breteler, head of the Erasmus center's neuroepidemiology research group.
The scans, performed in 1995 and 1996, found brain cell damage in 217 people that indicated a silent stroke. Over an average of 3.6 years of follow-up, 3 percent, or 30 people, developed dementia; 26 had Alzheimer's and four had other forms.
A stroke is a "brain attack" in which the flow of blood and oxygen to part of the brain is interrupted. Most often, it is caused by a blood clot or a hardening of arteries in the brain that cuts off blood flow; this type of stroke, called an infarct, was examined in the study.
Damage from a stroke, such as impaired mobility of speech, varies with a stroke's location and severity. But mental function often declines.
In dementia, mental ability usually declines gradually, impairing memory, learning skills, judgment and attention span. Alzheimer's disease, which also is linked to excessive buildup of proteins in the brain, accounts for about two-thirds of dementia cases.