Wednesday August 25,1999 5:56 PM ET

NEW YORK, Aug 25 (Reuters Health) -- Brisk walking can reduce a woman's risk of heart attack as much as vigorous exercise such as jogging, biking and swimming, researchers report in the August 26th issue of The New England Journal of Medicine.

``The study suggests that one third of heart attacks in women can be prevented by walking vigorously,'' the study's lead author, Dr. JoAnn E. Manson, of Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts, told Reuters Health in an interview.

It may not be surprising that women in the study who exercised vigorously for at least 1.5 hours per week reduced their risk of heart attack by 30% to 40%, but women who walked 3 hours each week at a pace of 20 minutes per mile achieved the same reduction, according to Manson and her colleagues. And women who walked briskly for 5 or more hours a week cut their heart attack risk nearly in half, they found.

Manson's team also found that sedentary women who began exercising during the study period were able to reduce their risk of heart attack.

``There is an epidemic of sedentary lifestyle in the US,'' Manson said, noting that about 60% of Americans do not exercise regularly.

`It's never too late to start exercising,'' she said. ``The key is to get up off the couch and start moving.''

The findings should add support to federal guidelines that recommend that everyone should participate in 30 minutes of moderate exercise on most days of the week, according to Manson.

The researchers based the findings on 72,488 women in the Nurses' Health Study who were ages 40 to 65 in 1986. At several times between 1980 and 1992, the women filled out questionnaires about their physical activity.

While there has been growing evidence that exercise can reduce the risk of heart disease, according to Manson, few studies have included women and few have focused on the benefits of walking, which is the most popular type of exercise among women. But even though the study included only women, ``there is no reason to believe that (these findings) wouldn't apply to men,'' Manson said.

Although the researchers note that vigorous exercise is appropriate for some people, they conclude that these findings ''indicate that enormous public health benefits would accrue from the adoption of regular moderate-intensity exercise by those who are currently sedentary.''

Dr. Gerald Fletcher, a national spokesperson for the American Heart Association and professor of medicine at the Mayo Medical School in Jacksonville, Florida, said in a statement: ''Brisk walking is an excellent form of exercise for both women and men, especially as they age and their risk for knee and other injuries increases.''

``These findings are right in line with the exercise recommendations of the American Heart Association, which are at least 30 to 60 minutes of moderate-intensity exercise 3 to 6 days a week,'' he added.

Health experts recommend seeking a physician's advice before beginning any exercise program.

SOURCE: The New England Journal of Medicine 1999;341:650-658.