If you are an older American with no major health problems, chances are about one in 10 that you have had a stroke and did not know it, according to a report in the medical journal Stroke.
It was probably not severe enough to cause recognizable symptoms, such as vision problems, facial weakness, or trouble walking, but it was still a blockage of a brain artery, and it reduced your thinking powers just a bit.
That estimate comes from a new study of 2,040 people, average age 62, in the long-running Framingham Offspring Study.
Magnetic resonance imaging (MRI) scans showed that 10.7 percent of them had experienced what study author Dr. Sudha Seshadri, at Boston University, calls "a silent brain infarct."
It is the cerebral equivalent of what physicians call a myocardial infarct - blockage of a blood vessel that causes damage to heart tissue. In the case of a silent stroke, the blockage and the damage occurs in the brain, without symptoms.
A silent stroke is different from a transient ischemic attack (TIA), a momentary loss of brain function, says Dr. Seshadri. A TIA causes some symptoms, while a silent stroke, by definition, does not.
But both are warning signs to pay attention to the well-known risk factors for stroke, such as cholesterol levels, blood pressure, obesity, and smoking.
The incidence found in the Framingham Offspring study "was within the ballpark of what prior studies have suggested," notes Dr. Seshadri.
"But this was a group of people who were younger than in most of the prior studies," she says. "The fact that one in 10 persons had silent attacks that had subtle side effects on the brain is something we should be concerned about and should address."
The effects of a silent brain infarct show up on an MRI scan as "small lesions in various parts of the brain," says Dr. Seshadri. "We can't tell from that whether they had a symptomatic attack."
And the MRI scans give no clues as to when the silent stroke occurred.
Testing showed that "on average, compared to age-matched controls, those with lesions do have subtle signs, such as loss of flexibility of talk," she says.
The incidence seen in the study did not startle Dr. Claudette Brooks, at West Virginia University Health Sciences Center.
"When I look for the cause of headaches and similar problems, it doesn't surprise me when I see these lesions, and other colleagues tell me they see them," says Dr. Brooks.
An even higher rate of silent strokes might be expected in a study of African Americans, she notes.
"They have a higher incidence of hypertension [high blood pressure], atherosclerosis, and hyperlipidemia [excess blood fat]," says Dr. Brooks.
Nothing special needs to be done to reduce the risk of silent stroke, both physicians say.
"I wouldn't recommend that people rush out to have an MRI," says Dr. Seshadri. "It's up to the medical and public health community to emphasize the importance of controlling risk factors."
"The whole thing boils down to modifying risk factors," explains Dr. Brooks. "If you don't have risk factors such as high cholesterol, obesity, and diabetes, try to keep yourself out of the group that does. If you do, modify them by keeping blood pressure and cholesterol down, things like that."
Always consult your physician for more information.
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Stroke is the third largest cause of death, ranking behind diseases of the heart and all forms of cancer.
Almost every 45 seconds in the United States, a person experiences a stroke.
Over 4 million US adults live today with the effects of a stroke.
The American Stroke Association (ASA) estimates strokes cost the US 62.7 billion in 2007.
Women account for about 6 in 10 stroke deaths.
Each year about 700,000 people suffer a new or recurrent stroke in the US.
Stroke accounts for about 1 out of every 16 deaths in the US.
Stroke, also called brain attack, occurs when blood flow to the brain is disrupted.
Disruption in blood flow is caused when either a blood clot or piece of plaque blocks one of the vital blood vessels in the brain (ischemic stroke), or when a blood vessel in the brain bursts, spilling blood into surrounding tissues (hemorrhagic stroke).
The brain needs a constant supply of oxygen and nutrients in order to function.
Even a brief interruption in blood supply can cause problems. Brain cells begin to die after just a few minutes without blood or oxygen. The area of dead cells in tissues is called an infarct.
Due to both the physical and chemical changes that occur in the brain with stroke, damage can continue to occur for several days. This is called a stroke-in-evolution.
A loss of brain function occurs with brain cell death.
This may include impaired ability with movement, speech, thinking and memory, bowel and bladder, eating, emotional control, and other vital body functions.
Recovery from stroke and the specific ability affected depends on the size and location of the stroke. A small stroke may result in only minor problems such as weakness in an arm or leg. Larger strokes may cause paralysis (inability to move part of the body), loss of speech, or even death.
According to the National Stroke Association (NSA), it is important to learn the three Rs of stroke:
Reduce the risk.
Stroke is an emergency and should be treated as such. The greatest chance for recovery from stroke occurs when emergency treatment is started immediately.
Always consult your physician for more information.