Physical activity apparently increases a woman’s chances of surviving breast cancer - regardless of her level of physical activity before the diagnosis - according to a new study in this week’s Journal of the American Medical Association.

Previous reports have suggested that physical activity may stave off breast cancer, but the beneficial effects after the disease has developed were unclear, Dr. Michelle D. Holmes, from Harvard Medical School in Boston, and colleagues note.

To investigate whether physical activity lowers the risk of dying from breast cancer, the researchers analyzed data from 2987 women who were enrolled in the Nurses’ Health Study and diagnosed with breast cancer between 1984 and 1998. The subjects were followed until June 2002 or until they died, whichever came first.

The risk of death from breast cancer fell as physical activity increased.

For example, women who engaged in more than 3 MET-hours of activity per week cut their risk of breast cancer mortality by 20 percent to 50 percent. Three MET (metabolic equivalent task)-hours is equal to walking at an average pace (2 to 3 m.p.h.) for 1 hour, the authors point out.

Nine or more MET-hours per week of physical activity was associated with a 6-percent reduced risk of death from breast cancer over a 10-year period, compared with less than 3 MET-hours per week.

“These results are consistent with a hormonal mechanism,” the investigators state.

“Women with breast cancer who follow the Centers for Disease Control and Prevention recommendations for all individuals in the United States to exercise at moderate intensity for 30 or more minutes per day for 5 or more days per week may survive longer.”

SOURCE: Journal of the American Medical Association, May 25, 2005.