Oct. 23 (HealthDay News) -- About 60 percent of the protection provided to women by exercise against heart disease and stroke comes from its effect on a few specific risk factors, says a U.S. study in the journal Circulation.

Researchers assessed cardiovascular risk factors and exercise levels in more than 27,000 women, ages 45-90 (average age 55) enrolled in the Women's Health Study who were followed for more than 11 years for new diagnosis of heart attack and stroke.

Women who exercised the most were 40 percent less likely to have a heart attack or stroke than those who did the least amount of exercise.

"Regular physical activity is enormously beneficial in preventing heart attack and stroke," lead author Dr. Samia Mora, instructor of medicine at Harvard Medical School in the divisions of preventive and cardiovascular medicine at Brigham and Women's Hospital in Boston, said in a prepared statement.

"We found that even modest changes in risk factors for heart disease and stroke, especially those related to inflammation/hemostasis and blood pressure, can have a profound impact on preventing clinical events. This study is the first to examine the importance of a variety of known risk factors in explaining how physical activity prevents heart disease and stroke," Mora said.

The Harvard team found that exercise-related changes in inflammatory and hemostatic biomarkers -- fibrinogen, C-reactive protein and intracellular adhesion molecule-1 -- had the largest impact, lowering heart attack and stroke risk by 33 percent.

"Inflammatory and hemostatic factors as a group have overlapping functions and roles and, in our study, had the biggest effect in mediating exercise-related cardioprotection, more so than blood pressure or body weight," Mora said.

Exercise-related improvement in blood pressure was the second most important (a 27 percent reduced risk), followed by lipids (blood fats), body mass index, glucose abnormalities, kidney function, and homocysteine.

Due to a lack of clinical evidence, the inclusion of inflammatory and hemostatic biomarkers as risk factors in assessing cardiovascular disease isn't yet recognized by the American Heart Association.

SOURCE: American Heart Association, news release, Oct. 22, 2007