Young women in the U.S. who are physically active have a lower risk of coronary heart disease, according to a prospective study that followed participants for 20 years.

The researchers noted that the total volume of physical activity was more important than the frequency of physical activity. They also mentioned that even moderate-intensity physical activity could reduce the risk of coronary heart disease and that physical activity was associated with a lower risk of coronary heart disease regardless of a woman’s body mass index (BMI).

Lead researcher Andrea K. Chomistek, ScD, of Indiana University, and colleagues published their results online in Circulation on July 25.

“Our results suggest that previously inactive women who become physically active can still decrease their risk of [coronary heart disease],” the researchers wrote. “It is important for normal weight, overweight and obese women to be physically active.”

The researchers analyzed 97,230 women who enrolled in the Nurses’ Health Study II, an ongoing cohort study that began in 1989 and mostly included white registered nurses who were between 25 and 42 years old at baseline.

The participants completed a self-administered questionnaire at baseline and follow-up biennial questionnaires on their physical activity, food frequency and other measures. The researchers assessed leisure-time physical activity in 1991, 1997, 2001, 2005 and 2009.

At baseline, the mean age of the women was 36.6 years old. During the 20 years of follow-up, 544 women developed coronary heart disease, including 254 women who were less than 50 years old.

The women who were more physically active tended to be younger and have a lower BMI, were less likely to smoke and watched less television.

A multivariable-adjusted analysis found that women who had the highest amount of leisure-time physical activity had a significantly lower risk of coronary heart disease compared with the least active women. The researchers defined a high amount of activity as 30 or more metabolic equivalent of task (MET)-hours per week and a low amount of activity as less than one MET-hour per week.

Women who reported at least 15 MET-hours per week of moderate-intensity activity had a 33 percent lower risk of coronary heart disease compared with women who reported no moderate-intensity activity. Meanwhile, women who reported at least 15 MET-hours per week of vigorous-intensity activity had a 23 percent lower risk of coronary heart disease compared with women who reported no vigorous-intensity activity.

Examples of moderate activities included brisk walking, outdoor work, yoga and weight training, while vigorous activities included jogging more than 10 minutes per mile, running less than 10 minutes per mile, bicycling, lap swimming, tennis, squash, racquetball and other aerobic exercise.

The researchers cited a few limitations of the study, including that it mostly included white nurses, so the results may not be generalizable to other groups. In addition, the observational design meant that the study could be subject to residual confounding by other lifestyle characteristics. Still, they adjusted for several known coronary heart disease risk factors.

“Most women can improve their heart health significantly by incorporating some moderate or vigorous physical activity into their regular routine,” Chomistek said in a news release. “Physical activity appears to be beneficial across the lifespan, regardless of body weight. It’s important to remember that any amount of activity is better than none.”