Postmenopausal women who do moderate or vigorous activities for an hour a day can lower their breast cancer risk by 14 or 25 percent, respectively, according to a recent study. American Cancer Society (ACS) researchers sought to examine the effects that physical activity, such as walking and exercising, had on the breast cancer status of 73,615 postmenopausal women. The participants of the study were identified from a large cohort of 97,785 women aged 50 to 74 years, recruited between 1992 and 1993 for the Cancer Prevention Study-II Nutrition Cohort, a prospective study of cancer incidence established by the ACS, according to Medical Xpress.  

The women were asked questions about their health, medications, and exercise habits starting in 1992. They reported the average number of hours they spent on various physical activities including walking, jogging, swimming, playing tennis, bicycling, and performing aerobic exercises every week in 1999, 2001, and 2005. In addition, the participants had to include the number of hours they spent leisurely sitting, watching television, and reading. Between 1992 and 2007, approximately 6.5 percent, or 4,760 women in the study, were diagnosed with breast cancer, Reuters Health reports.

The researchers found that, among all women in the group, 47 percent said walking was their only recreational activity. The participants were also more likely to take part in walking, dancing, or aerobics than in very active sports like running, swimming, and tennis. Women who reported walking as their only activity and walked at least seven hours a week had a 14 percent lower risk of breast cancer than those who walked three hours or less in a week.

Women who did vigorous activities for an hour a day had a 25 percent lower risk of breast cancer than their less active counterparts. Overall, the researchers concluded that the more physical activity a postmenopausal woman does, the less risk she faces of developing breast cancer.

"Our results clearly support an association between physical activity and post-menopausal breast cancer, with more vigorous activity having a stronger effect,” said Dr. Alpa Patel, senior author of the study and senior epidemiologist at the American Cancer Society in Atlanta, reports The Guardian. “Without any other recreational physical activities, walking on average of at least one hour per day was associated with a modestly lower risk of breast cancer."

The study is the first to report a lowered risk of breast cancer in postmenopausal women, in relation to walking. While strenuous activities did decrease the risk of breast cancer even more, the researchers marveled at how a moderate activity, such as walking, was associated with a lower risk of breast cancer. In other words, women do not need to be marathon runners in order to reduce their risk of the disease, says Dr. Patel.

"You can pick up 10 minutes at the grocery store, another 10 minutes when you're out shopping or another 10 or 15 minutes at work… You can pick up your hour pretty quickly," Dr. Steven Chen, an associate professor at City of Hope in Duarte, Calif., told Reuters Health.

In light of this, women are warned against excessive sitting, which is tied to a higher risk of breast cancer. "The more you sit, the higher the likelihood of you developing cancer," Dr. Chen said. "So of course we encourage people to be as active as they can."