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Silent Strokes and Alzheimer's: Break the Connection

The discovery of a link makes prevention more crucial than ever

By Elizabeth Hanes | May 16, 2012

Silent strokes are a silent epidemic among older Americans. It's estimated that Americans experience more than 11 million each year. A stroke, or infarct, occurs when blood flow to any part of the brain is blocked or interrupted, preventing oxygen from reaching brain tissue. Without oxygen, brain cells can die. Classic symptoms of strokes can include slurred speech, dizziness, numbness, memory loss, and paralysis of varying duration and severity. Americans suffer about 750,000 strokes with these symptoms each year. When strokes affect a small area, they are "silent," with none of these visible symptoms.

“Biologically, silent stroke is the same as regular stroke, except there are no obvious [external] signs," says Dr. Adam Brickman of the Taub Institute for Research on Alzheimer’s Disease and the Aging Brain at Columbia University Medical Center in New York. But that's not to say silent strokes are not significant, or dangerous.

Discovering a Link

Brickman recently piloted a study of 658 people without dementia age 65 or over. His team conducted MRI scans of the subjects' brains and gave them memory, language, and other neurological tests. The study's results confirmed that people who had a shrunken hippocampus, the area of the brain responsible for memory, performed less well on the tests. But there was more: Subjects whose MRI results showed evidence of silent strokes, about a quarter of the group, also scored less well on the memory tests, even if they did not have a shrunken hippocampus.

Brickman believes the results point to silent stroke as an independent risk factor for developing conditions in which memory is impaired, like Alzheimer's disease. "Our research finding led us to consider that Alzheimer’s may also have a vascular component," he says. "In some ways, that would be good news."

The incidence of silent strokes and shrinking of the hippocampus were separately associated with memory loss in Brickman's study. If people do more to prevent silent strokes, then, they may be more successful in warding off dementia and Alzheimer's as well. "Our results support stroke prevention as a means for staving off memory problems," he says. "If we can control all those risk factors, then we think we might be able to reduce the burden of Alzheimer’s or minimize the risk.”
 
5 Steps to Ward Off Strokes, and Alzheimer's

Brickman's research makes the case that treating your heart well and reducing your risk factors for stroke can help you stave off Alzheimer's disease as well. “Tried and tested treatments can reduce the risk of stroke greatly,” says Dr. Aneesh Singhal of Harvard Medical School. Here are five things you can do to limit your risk:
 
Maintain a healthy weight. Obesity increases your likelihood of developing hypertension, high cholesterol, and Type II diabetes – all risk factors for stroke or silent stroke because of their impact on blood circulation. "Central" obesity, in which extra weight is carried around the waist (not the hips), heightens the risk, as abdominal fat can increase the production of "bad" (LDL) cholesterol, the type that clogs blood vessels. Seek out reputable resources on eating healthier, such ChooseMyPlate.gov.

Control your blood pressure. "Treating hypertension can reduce your risk of stroke by 30%," Singhal says. High pressure in your blood vessels can cause them to burst in the brain, causing a hemorrhagic stroke. Get your blood pressure checked regularly; reduce salt consumption if it’s high or borderline -
“even borderline hypertension is critical to control,” Brickman says; take any prescribed medications regularly; and exercise - it keeps your entire cardiovascular system running smoothly. “The higher proportion of their life people spend exercising, the better," Brickman says.

Lower your cholesterol levels. Cholesterol can block arteries and prevent them from delivering oxygen to the brain, so a high cholesterol level represents a primary risk factor for stroke. “Getting more fiber into your diet is crucial,” Singhal says, “particularly in the form of fresh fruits and vegetables. This has a positive impact on reducing cholesterol." If your cholesterol runs high, consult your doctor about appropriate medications and take them as prescribed. And, again: Exercise.

Treat your Type II diabetes. Diabetics are at greater risk for stroke in part because they often have other related health problems such as high cholesterol, hypertension, obesity, or a type of irregular heartbeat known as atrial fibrillation. If you have Type II diabetes, avoiding sugar, eating healthier, and losing weight can help alleviate risks, as can routinely checking your blood sugar levels and taking prescribed medications regularly. Effective treatment of Type II diabetes, Singhal says, can reduce the risk factor for stroke by 25%.

Quit smoking. Smoking has been linked to atherosclerosis, or hardening of the arteries, so quitting reduces your chance of stroke due to the inability of inflexible blood vessels to deliver oxygen to the brain. 
 
Learn more about strokes and Alzheimer's disease from our partners at MedlinePlus.