A study in the Oct. 1 issue of BMC Cancer suggests that menopausal women who adhere to regular, moderate vigorous physical activity can reduce breast cancer incidence, even among women who did not exercise in the past. Among a number of modifiable breast cancer-related risk factors, high versus low physical activity consistency reduced the incidence of menopausal breast cancer by 20-40%,” Dr. Tricia M. Peters of the National Cancer Institute in Maryland writes in the article. To better define the relationship between physical activity and breast cancer incidence, further research on physical activity-specific parameters, such as intensity and duration, may be more effective in preventing breast cancer incidence among menopausal women. The study began in 1995 and included 118,899 women aged 50 to 71 years who submitted their exercise habits by questionnaire for four stages of life: 15 to 18 years, 19 to 29 years, 35 to 39 years, and the past decade. Participants also answered the number of hours of exercise per week, ranging from less than 1 hour to more than 7 hours, and whether the activity was light (e.g., bowling and fishing), moderate to vigorous (e.g., jogging and swimming). At 6.6 years of follow-up, 4,287 of the study participants developed breast cancer, most of which were estrogen receptor positive. The researchers found that women who maintained vigorous physical activity for more than seven hours per week in the decade prior to the study had a 16 percent lower incidence of breast cancer compared to women of the same age and multivariate with the same sedentary lifestyle. Adjusting for light physical activity in the most recent decade did not affect the results. Further adjustment for body mass index had a mild effect on the relationship between exercise and breast cancer incidence. The authors noted that recent physical activity was more effective than historical physical activity in reducing the incidence of breast cancer in menopausal women. Reasons why physical activity may reduce the incidence of breast cancer may include the following factors: physical activity reduces endogenous sex hormone levels, regulates insulin and insulin-like growth factors, enhances immunity, and reduces impending inflammation.