A new study seems to settle an old debate on the value of brisk walking versus vigorous exercise for women in cutting heart disease risk. The winner: brisk walking (if it’s really brisk).

In the study, women who walked at 3 mph (or one mile every 20 minutes) at least three hours per week had a 30 percent to 40 percent lower risk of heart attack than sedentary women.

In effect, they achieved the same reduction in heart risk as women who engaged in vigorous exercise such as aerobics, jogging and bicycling. Still, the more women walked, the study found, the lower their risk. Those who walked briskly five hours per week cut their risk of heart disease in half compared with those who were less active.

The study, published in the August 26 New England Journal of Medicine, tracked 72,488 female nurses age 40 to 65. They are part of a larger Nurses’ Health Study at Brigham and Women’s Hospital in Boston, which is tracking thousands of healthy women to find out the risks of certain diseases.

"The important caveat is that the heart protection does not apply to casual strolling and window-shopping at the mall," said JoAnn E. Manson, professor of medicine at Harvard Medical School and lead author of the study.

The study is the first to show the effectiveness of brisk walking in curbing heart disease in women. Earlier studies (which produced similar results) were conducted on men.