March 27, 2003
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 Association.
"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."
In an editorial, Drs. John Blass and Rajiv Ratan of Cornell University's Weill Medical College said the study and other evidence indicate inadequate blood flow in the brain is an underlying cause of both Alzheimer's and stroke -- and that silent stroke may be the first sign of Alzheimer's, not just a risk factor.
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 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 followup, 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 difficulty speaking or weakness in a limb, varies with the 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.
Along with following the 1,015 patients to see who developed dementia, the researchers did a second MRI on 619, some of whom had had additional silent strokes. Mental decline was even more severe in those people, as well as those who had lesions deep inside the brain from narrowed blood vessels, Breteler said.
Because many people who did not undergo a second MRI were in poorer shape mentally, Breteler said, the researchers probably underestimated how much silent strokes increase risk of dementia.
Many people with Alzheimer's have standard risk factors for stroke and heart disease. Those include elevated blood pressure, cholesterol and blood sugar levels; eating a diet high in fat and low in vegetables; smoking; and getting little or no exercise.
Getting the elderly to follow health guidelines to reduce or eliminate those risk factors could prevent dementia or strokes, Breteler said.
Blass and Ratan suggested the same steps for patients in whom a brain scan found a silent stroke, along with careful monitoring by a doctor and taking a daily baby aspirin.
"It's another reason for keeping your cardiovascular system healthy," said Dr. Patrick Pullicino, chairman of neurology and neurosciences at University of Medicine and Dentistry of New Jersey in Newark. "This is simple, common sense."