A few hours of walking or other exercise each week may help breast cancer survivors live longer, new research suggests. In the study of nearly 3,000 women, those who exercised this amount were less likely to die of their breast cancer than women who got less than 1 hour of physical activity each week.

The finding could give women another way to boost their odds of beating breast cancer, experts said.

"Women with breast cancer have little to lose and much to gain from exercise," said the study's lead author Michelle Holmes, MD, DrPH, of Harvard Medical School and Brigham and Women's Hospital in Boston. "We already know that [breast cancer patients who exercise] have better mood, better body image, and better self-esteem. We know it fights other diseases that women with breast cancer can also get, like heart disease and diabetes. And it may also help these women avoid dying from breast cancer."

Holmes and her colleagues published their findings in the Journal of the American Medical Association (Vol. 293, No. 20: 2479-2486).

The women involved had all been treated for stage 1, 2, or 3 invasive breast cancer with standard therapies like surgery, radiation, chemotherapy, and tamoxifen. The researchers asked the women how often they exercised during their free time after they had finished treatment. Activities included walking, hiking, jogging, or running, as well as cycling, swimming laps, tennis, aerobics, squash, racquetball, or using a rowing machine.

They compared the intensity level of each form of exercise with breast cancer survival, taking into account factors like body mass index, hormone use, and menopausal status (among others) that might have an effect on survival.

Women who exercised the equivalent of walking about 1 hour a week, at a 2-3 mile-per-hour pace, had a lower risk of dying from breast cancer than women who got less than an hour's worth of physical activity each week. Women who did a little more than that -- the equivalent of walking about 3-5 hours per week at that pace -- had the lowest risk of dying. Women who got more exercise than that also had a lower risk of dying, but not as low as women in the middle group.

"The benefit seemed to level off," Holmes said, "so the good news is women don't have to run marathons to get the maximum benefit."

The benefit was about the same for women who were past menopause and those who had not yet reached menopause.

However, the benefit was statistically significant only in women whose tumors were sensitive to estrogen (ER+ tumors). That makes sense, Holmes said, because exercise reduces levels of estrogen in the body. She noted, though, that there were relatively few women with ER- tumors in the study, so it's not possible to draw firm conclusions about whether exercise can help them survive longer, too.

After 10 years of follow-up, 92% of the women who exercised 3-5 hours per week (or about half an hour per day) were still alive, compared to 86% of those who got less than an hour a week of physical activity. Holmes said it didn't matter if the exercise was done all at once or spaced throughout the day.

The amount of exercise that was helpful is right in line with what the American Cancer Society recommends for cancer survivors, said Debbie Saslow, director of breast and gynecologic cancers for ACS. Until there are more studies on lifestyle issues and cancer recurrence, ACS advises survivors to follow its Nutrition and Physical Activity Guidelines for Cancer Prevention. Those recommend that adults get at least 30 minutes of moderate activity on 5 or more days of the week, and that for breast cancer risk reduction, 45 minutes or more may be even better.

"It's great that we can tell women there's something they can do that's not going to have horrible side effects," Saslow said. "Even though the effect is not huge, a lot of new treatments don't make a bigger difference than this, and some make a whole lot less."

Holmes said women should not think of exercise as a replacement for standard breast cancer treatment. And Saslow said it's not the only factor that could influence a woman's survival.

"We need to make sure women understand that survival rates for breast cancer are high regardless of whether women exercise or not. Women who are unable to be physically active should not feel that they are harming themselves, and women who do follow the physical activity guidelines have no guarantee against a recurrence " she said. "But that's true of every drug or intervention.

"However, this study shows that in addition to the quality of life benefits, following ACS activity guidelines can make a significant difference for breast cancer survival," Saslow added.