Older women who walk just four hours per week can dramatically reduce their risk of breast cancer, a new study suggests.
In the study, researchers examined the activity levels of postmenopausal women within the past four years. They found that those who had engaged in regular physical activity, equivalent to at least four hours of walking per week, had a 10 percent decrease in their risk of developing invasive breast cancer compared with women who exercised less, including those who didn't exercise at all.
"The results of our study are consistent with the World Cancer Research Fund recommendation of walking 30 minutes per day," said study author Agnès Fournier, a researcher at the Centre for Research in Epidemiology and Population Health at the Institut Gustave Roussy in Villejuif, France. "The study also indicates that engaging in vigorous or very frequent activity is not necessary to receive the protective benefits of exercise."
The researchers analyzed data from more than 59,000 postmenopausal women over 12 years, from 1993 to 2005. The women completed biennial questionnaires, and their levels of physical activity were self-reported in 1993, 1997 and 2002. At a follow-up 8.5 years later, the researchers determined that 2,155 of the women had been diagnosed with invasive breast cancer.
"The literature reporting the association between regular physical activity and reduced breast cancer risk after menopause has been pretty consistent," Fournier told Live Science. "In our study, we wanted to examine how rapidly this association is observed after regular physical activity is begun and for how long it lasts once women stop exercising." [ 6 Foods That May Affect Breast Cancer Risk ]
The findings illustrated that the benefit of exercise dropped once women stopped being active. "Women who engaged in this level of physical activity between five and nine years earlier, but who were less active in the four years prior to the study, did not have a decreased risk for invasive breast cancer," she said.
The results of the study are published in the August 2014 issue of Cancer Epidemiology, Biomarkers & Prevention.
"Women currently participating in physical activity should be encouraged to continue in order to receive the protective benefit of exercise," Fournier said. "And, for those who do not exercise, it is recommended they start, as their risk of breast cancer may decrease rapidly."