WEDNESDAY, June 8, 2011 (Health.com) — Small strokes that cause no outward symptoms yet have potentially serious long-term consequences may be kept at bay by vigorous exercise such as jogging and cycling, a new study in the journal Neurology suggests.

Walking and other light exercise, by contrast, appears to offer no protection against these so-called silent strokes, which cause small brain lesions and have been linked to an increased risk of falling, memory problems, dementia, and full-blown strokes.

"The more reasons we can tell our geriatric patients to exercise, the better," says the lead author of the study, Joshua Z. Willey, MD, an assistant professor of neurology at Columbia University Medical Center, in New York City. "Not only does [exercise] prevent stroke and heart disease, it also prevents these markers that are linked to other diseases, including dementia, and overall mortality."

The study included 1,238 men and women in northern Manhattan who are part of a larger, ongoing study of stroke risk factors funded by the federal government. The participants ranged in age from about 60 to 80 and had no known history of stroke. Just under two-thirds were Hispanic, and the remainder were roughly evenly split between blacks and whites.

Each of the participants answered survey questions about their exercise habits, including which activities they took part in, how often, and for how long. Forty-three percent of the participants did not exercise at all; 36% engaged in light workouts such as walking, playing golf, or bowling; and 21% reported getting regular, moderate-to-vigorous exercise from bicycling, swimming, racquetball, and similarly intense activities.

Roughly six years later, the participants each underwent an MRI to look for signs of silent strokes, also known as subclinical brain infarcts. Roughly 1 in 6 had lesions consistent with silent stroke.

The odds of having a silent stroke were 40% lower in the heavy exercise group than in the sedentary group. However, the light exercisers were just as likely to have lesions as those who did not exercise at all, even when the researchers took other risk factors (such as cholesterol levels, blood pressure, and diabetes) into account.

This doesn't mean that low-intensity exercise has no value. As Dr. Willey and his coauthors are quick to point out, light physical activity has other health benefits. It's also possible that, with a larger study population, they might have found a subtle yet measurable relationship between low-intensity exercise and a lower risk of silent stroke.

"Maybe it was simply that they could not measure a difference," says Helmi Lutsep, MD, a stroke expert and vice chair of neurology at Oregon Health and Science University, in Portland.

But the findings do echo similar research on exercise and (non-silent) strokes. Previous studies, including one from Dr. Willey's team, which includes researchers at Columbia and the University of Miami, have consistently linked vigorous exercise—but not mild exercise—to a lower risk of stroke.

Dr. Lutsep, who was not involved in the study, says that some of her elderly patients have difficulty sticking to a regular regimen of intense exercise. She often advises these people to include short bursts of intense activity in their exercise routine.

"Even if they can't maintain an intense level of activity, they can often make their exercise a little more vigorous for a short time, for, say, 10 minutes," she says.

One of the study findings surprised Dr. Willey: Uninsured participants, as well as those with Medicaid, saw no reduction in silent-stroke risk no matter how vigorously they exercised. While he's unable to explain why, he suspects that it's because those participants have underlying medical problems that are not being adequately treated.

Dr. Lutsep agrees. "If we have a patient who is uninsured, it's likely he's not taking blood-pressure medications that help prevent strokes," she says. "The risks are magnified."