by Wayne Lewis and Alicia Di Rado

A long-term habit of consistent exercise appears to improve women’s chances of surviving breast cancer, according to researchers at City of Hope and their colleagues.

The findings, published Oct. 20 online in Cancer Epidemiology, Biomarkers & Prevention, provide further evidence of the importance of public health strategies to encourage an active lifestyle, researchers said.

Leslie Bernstein (Photo by Walter Urie)

According to the study, women who exercised moderately or strenuously an average of more than a half hour each week since their teen years had less risk of dying from their breast cancer than similar women who did little or no exercise. The protective effects were strongest among overweight women.

The findings draw from the California Teachers Study, which is led by City of Hope’s Leslie Bernstein, Ph.D., professor and director of the Division of Cancer Etiology. Bernstein was senior author on the paper, which was co-authored by scientists at the Keck School of Medicine of the University of Southern California (USC) and the Northern California Cancer Center. USC’s Carmen Nicole West-Wright, M.S., who did her graduate work with Bernstein at City of Hope, was lead author.

“A substantial body of work has clearly shown a link between regular physical activity and reduced breast cancer risk for healthy women,” said Bernstein. “But research is sparse on whether physical activity may influence survival for women who develop breast cancer, so we wanted to take a closer look.”

The California Teachers Study, begun in 1995, follows more than 130,000 women, teachers and administrators in the California public school retirement system. For the latest investigation into physical activity, scientists focused on more than 3,500 women in the study who were diagnosed with breast cancer before 2005.

They compared women’s cancer outcomes and body mass indexes, as well as their exercise habits from their late adolescence through the end of reproductive age.

The scientists made these findings:

• Those who exercised at an intermediate level through their adult life had a 35 percent lower risk of breast cancer death than less active breast cancer patients.
• Intermediate-level exercisers who were overweight had a 48 percent lower risk of death from breast cancer.
• Women who exercised at a high level during their adult life had 47 percent less risk of breast cancer death than less active breast cancer patients.
• Overweight high-level exercisers had a 59 percent lower risk of death from breast cancer.

“We know that being overweight or obese is related to a poorer prognosis in women with breast cancer, so the positive effect of activity in this population is particularly encouraging,” Bernstein said. “In addition, we saw that activity reduced breast cancer death both for women with estrogen-receptor-negative and those with estrogen-receptor-positive cancer, and for all stages of breast cancer.”

Exercise suppresses levels of important hormones such as estrogen, insulin and insulin-like growth factor, especially among overweight women, who have higher levels of such hormones than lighter women. Elevated levels of these hormones are believed to be linked to breast cancer, so hormone suppression may explain the lower risk of breast cancer-related deaths among overweight breast cancer patients.

The researchers did not study whether physical activity after diagnosis influenced their chances of survival. However, Bernstein noted, other studies have shown that women who are active after diagnosis are less likely to die of breast cancer or other diseases.

“We think their results are so similar to those in our study because women who exercise after diagnosis are those who have had a lifestyle throughout life that included regular exercise,” she said. “Women who make a habit of exercising tend to keep exercising.”

The National Institutes of Health and the California Breast Cancer Research Fund provided grant funding for the study. Data collection was supported by the California Department of Health Services, the National Cancer Institute and the Centers for Disease Control and Prevention.