Lifestyle practices key in lowering breast ca risk.(Gynecology)

SAN ANTONIO -- The three most practical public health-type lifestyle interventions at present for reducing breast cancer risk are to encourage breast-feeding, get young girls started exercising regularly to lay the groundwork for a lifelong habit of physical activity, and tackle the postmenopausal obesity epidemic, Leslie Bernstein, Ph.D., said at a breast cancer symposium sponsored by the Cancer Therapy and Research Center.

Dr. Bernstein has spent most of her career studying the breast cancer-preventive effects of physical exercise. Indeed, she conducted the first epidemiologic study demonstrating the link. Since then, there have been more than 30 studies from around the world, most showing that lifetime physical activity is independently associated in dose-dependent fashion with a reduction in breast cancer risk of up to 20%-30%, compared with that of women who don't exercise.

The association has held true in studies of European, Asian, Asian American, and Hispanic American women. Most recently, Dr. Bernstein and coworkers reported the findings of the Women's Contraceptive and Reproductive Experiences (Women's CARE) study, the first-ever epidemiologic study focusing on the effects of lifetime recreational exercise on breast cancer risk in African Americans.

Women's CARE involved 1,605 black and 2,933 white women aged 35-64 years with breast cancer, and 1,646 black and 3,003 white controls. There were no racial differences in the impact of lifetime physical activity on breast cancer risk. Black or white, a woman's average number of hours of weekly exercise from age 10 onward was inversely associated in graded fashion with her risk of developing breast cancer. The highest level of recreational physical activity--defined in this study as an average of 3 hours or more per week over a woman's lifetime--was independently associated with roughly a 25% reduction in risk, compared with that of sedentary women (J. Natl. Cancer Inst. 2005;97:1671-9).

The risk reduction is greater in women without a first-degree family history of breast cancer. "I wish it were the other way around ... But at this point in time, none of my studies have shown a very strong benefit for women with a family history of breast cancer," said Dr. Bernstein, professor of preventive medicine at the University of Southern California, Los Angeles.

She said the field of breast cancer risk reduction through physical activity "still has a long way to go."

Remaining research questions include what the best type of activities would be, how much is needed, at what key ages, and the mechanism of benefit. Although the mechanism is widely assumed to be hormonal, it could, for example, involve anti-inflammatory effects or changes in insulin-like growth factors.