October 08, 1998
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Exercise Can Reduce Stroke Risk, Study Says

By William J. Cromie

Gazette Staff

Here's a research finding that should bring you to your feet. A brisk, hour-long walk, five days a week, can cut your risk of having a stroke almost in half.

Too much? Try 30 minutes a day, five days a week. That could decrease your risk by a quarter, or 24 percent.

Said another way, physical activities that burn 1,000 to 2,000 calories a week lower the risk of stroke 24 percent, while energy expenditures of 2,000 to 3,000 calories cut the risk by 46 percent. No increase in protection was associated with higher levels of exercise. The researchers do not know why that is.

"Our findings support the [U.S.] Surgeon General's recommendation that calls for at least 30 minutes of moderate-intensity physical activity on most days of the week." says I-Min Lee, an epidemiologist at the School of Public Health. "We found that doubling that recommendation produces an even greater reduction in stroke risk."

The finding comes from a study of 11,130 males who graduated from Harvard University between 1916 and 1950. There were no women graduates during that time, but Lee points out that other studies show that females gain similar stroke protection from exercise.

Not all types of exercise are equally effective. Activities of moderate intensity such as brisk walking, stair-climbing, bicycling, and gardening work best. "Light activity such as bowling and general housekeeping did not have the same effect," Lee said.

Lee and her colleagues define moderate intensity as expending at least 4.5 calories per kilogram (2.2 pounds) of body weight per hour. Besides brisk walking, about three hours of tennis a week burns nearly 2,000 calories, as does four hours of golf, if you carry your own clubs.

Exercise Once Thought Harmful

The result is well worth working up a good sweat. In the United States, strokes kill more than 150,000 people a year, mostly those who are 65 or older. "Brain attacks" are also the leading cause of serious, long-term disability in the United States.

Results from the Harvard alumni study were released today by the American Heart Association. Lee conducted the research with Ralph Paffenbarger, a pioneering epidemiologist who began tracking the health of Harvard graduates in 1962.

At that time, the kind of exercise recommended today was thought to be harmful to the heart. Paffenbarger was one of the first to find it protects men from heart disease. He showed, for example, that the risk of heart disease during middle age is decreased by participation in sports, at least to age 50. After that, the protective effect disappears unless men keep up a moderate level of physical activity.

The alumni study also demonstrates that it is never too late to begin exercising. "Sedentary college students who later took up an active and fit way of life were at a lower heart risk than former varsity players who gave up or reduced physical activity in middle age," Lee said.

In addition to protecting against stroke and heart disease, the Harvard research and several other studies show that moderate levels of exercise cut the risk of diabetes and colon cancer in both men and women.

It's logical to think that physical exercise protects against heart disease and strokes by reducing weight, lowering blood pressure, and maintaining normal levels of blood sugar. However, when Lee and Paffenbarger adjusted the alumni study results for weight, high blood pressure, and diabetes, these factors did not account for the bulk of the benefit. The authors noted that other protective factors may include a better cholesterol pattern (less low-density and more high-density cholesterol) and decreased levels of platelets and other clotting agents in the blood.


Copyright 1998 President and Fellows of Harvard College