"Anything is better than nothing," Dr. Melinda L. Irwin of the Yale School of Medicine in New Haven, Connecticut, one of the researchers on the study, told Reuters Health. "We actually observed benefits with just doing a little bit of exercise."
Dozens of studies over the past two decades have shown that exercising can reduce breast cancer risk by up to 40 percent, while more recent research has found that activity has equal or even greater benefits for survival among women with the disease.
To better understand the timing and amount of physical activity necessary to improve survival, Irwin and her team looked at 933 women who had been diagnosed with breast cancer between 1995 and 1998 and were followed until 2004.
They found that women who got the equivalent of at least two to three hours of brisk walking each week in the year before they were diagnosed with breast cancer were 31 percent less likely to die of the disease than women who were sedentary before their diagnosis.
Two years after diagnosis, the women who did any recreational activity at all had a 64 percent lower risk of dying than women who were inactive at that point, while women who got at least two to three hours of brisk walking in weekly reduced their risk of death by 67 percent.
Women who decreased their physical activity after diagnosis were actually four times more likely to die of breast cancer than those who were sedentary and remained so, Irwin and her colleagues found. But those who had been inactive and started exercising after being diagnosed cut their death risk by 45 percent.
Women undergoing breast cancer treatment should think of exercise as a part of their therapy, Irwin said, and be sure to make the time for it, even just by beginning with a 15-minute walk every other day.
Being active isn't only beneficial for survival, Irwin said; it may also help with the increased cardiovascular disease risk that may accompany treatment, and will certainly improve women's quality of life in many ways. "Hopefully this study shows what a major benefit exercise can be," she said.