Although shorter bursts of intense exercise burn calories as well as long periods of moderate exercise, the average woman cannot keep up such activity, Lee said in an interview with Reuters Health.
"The good news for women," she said, "is that even if you're sedentary and you begin walking, you can reduce your heart disease risk."
In the study, Lee's team followed the women for 5 years. The researchers found that women who burned more than 600 calories a week through exercise of any kind were about half as likely as women who burned less than 200 calories to have heart disease. It did not matter, however, whether they burned the calories through intense or moderate activity.
Among women who walked regularly--by far the most common exercise--the amount of time spent walking determined the heart benefit. Those who typically walked an hour or more had about half the heart disease risk of those who walked less than an hour. These exercise benefits held even after Lee's team factored in risk factors for heart disease, such as smoking, high blood pressure, and high cholesterol.
Moreover, Lee added, calorie burning cut heart disease risk even in women who smoked or were overweight, although the effect was not as dramatic as it was among nonsmokers and women of normal weight. "That was one of the most interesting things to me," Lee said. "(Moderate) exercise is beneficial even in some high-risk women."
Women's hearts, according to Lee, may respond to exercise differently than men's. In previous research in middle-aged and older men, she found that exercise intensity was important in cutting heart disease risk. Lee believes that may be because men tend to be more aerobically fit than women, so that exercise needs to be more vigorous to meaningfully reduce heart disease risk.
For the average American woman, though, walking could be the ideal exercise, according to Lee. "It's easy to do," she said. "You don't need special clothes or equipment, and you don't need a lot of coordination."
