By the time people reach their 70s, one in three has a silent stroke every year. The researchers also found that some people have more than one silent stroke in a year. When these repeat ones are added together, Americans have almost 22 million silent strokes annually. This means that only 3 percent of the total number of strokes in 1998, when the data were compiled, were actually diagnosed. Leary based her estimate on two surveys involving brain scans on about 5,500 Americans.
Doctors can see the scars left by silent strokes when they perform routine brain scans.
But ordinarily they do not search for them. However, the new data raise the possibility that perhaps they should, since people who have one silent stroke are likely to have many more. Strokes can be prevented by keeping blood pressure under control, lowering cholesterol, treating diabetes and stopping smoking. Leary said if people actually know they have had a silent stroke, they might be more willing to stick to blood pressure medicines and cholesterol-lowering drugs that cut their risk. In a separate study, Dutch doctors did brain scans on a cross-section of 1,077 elderly people.