TUESDAY, May 24, 2005 (HealthDay News) -- If you have breast cancer and have undergone treatment for it, there's one more thing you can do to increase the odds you'll survive the disease: exercise.
The good news is that you don't have to run marathons to reap the benefits: Women who spent three to five hours of walking or two hours of jogging a week cut their risk of death from breast cancer by 50 percent, according to a study in the May 25 issue of the Journal of the American Medical Association.
"Women with breast cancer have little to lose and much to gain from exercise," said study author Dr. Michelle Holmes, an assistant professor of medicine at Harvard Medical School. "Exercise contributes to better moods, higher self-esteem and it fights other diseases like heart disease and diabetes. And exercise may help women with breast cancer to avoid dying from that disease."
Holmes was quick to point out, however, that exercise doesn't replace any form of treatment.
In the study, Holmes and her colleagues suggest that exercise reduces levels of the hormone estrogen, which acts as a fuel for many breast cancers.
"Estrogen in the body is the primary factor involved in breast cancer and breast cancer risk," said Debbie Saslow, director of breast and gynecologic cancer for the American Cancer Society. "Anything we do for prevention -- losing weight, not drinking alcohol -- is directed at lowering estrogen. And, in all populations, physical activity decreases the amount of estrogen circulating in the body."
In a prospective observational study, Holmes and her colleagues followed breast cancer survivors from two years after their treatment until their death or June 2002, whichever came first.
Almost 3,000 women were included in the analysis. All were enrolled in the ongoing Nurse's Health Study and had been diagnosed with stage I, II or III breast cancer between 1984 and 1998.
The researchers asked the women about their physical activity seven different times throughout the study period. Their physical activities were assigned a metabolic equivalent score (MET) based on the energy used for that activity. Sitting quietly for an hour is one MET hour, while walking at an average pace of 2 to 2.9 mph for an hour is the equivalent of three MET hours. Jogging for an hour is seven MET hours and running for an hour is 12 MET hours.
Survival benefits were seen starting at three to 8.9 MET hours a week. Women who exercised 3 to 8.9 MET hours a week had a 20 percent decrease in the risk of death from breast cancer, compared to women who exercised less than three MET hours a week. Women who exercised nine to 14.9 MET hours a week cut their risk of dying by 50 percent.
However, greater amounts of exercise than that didn't seem to confer greater breast cancer survival benefits.
Women who exercised for 15 to 23.9 MET hours had a 44 percent risk reduction, while women who did more than 24 MET hours of exercise weekly had a 40 percent decrease in their risk of dying from breast cancer.
Holmes said she was surprised the risk reduction from exercise leveled off, and that there wasn't additional benefit from additional exercise.
After 10 years, the absolute unadjusted risk of dying from breast cancer was reduced by 6 percent for women who exercised at least nine MET hours a week.
"Exercise confers a small benefit, but it's there. Every little bit helps, and it's something women can easily do," said Saslow. Plus, she added, women should be physically active for the overall health benefits exercise confers, not just to reduce their risk of dying from breast cancer.
"Most women survive breast cancer and die from heart disease later," Saslow said.
She said the American Cancer Society recommends that anyone who isn't currently exercising should try to work up to 30 minutes a day at least five times a week, after checking with their doctor to make sure they can safely exercise.
And, she added, anyone who's already active should aim for 45 minutes to 60 minutes of daily activity that is slightly more than moderately paced most days of the week.
To learn more about exercise after a cancer diagnosis, visit the American Cancer Society.