What's more, the activity need not be strenuous but it should be done consistently, such as taking a brisk, 30-minute walk five days a week, said lead investigator Anne McTiernan, M.D., Ph.D., a member of Fred Hutchinson's Public Health Sciences Division and director of the center's Prevention Center.
"We thought it was important to determine if moderate-intensity physical activities, such as walking, biking outdoors or easy swimming, when initiated later in life, can reduce the risk of breast cancer, since these types of activities are achievable for most women," said McTiernan, who is also the lead author of "Breast Fitness: An Optimal Exercise and Health Plan for Reducing Your Risk of Breast Cancer" (St. Martin's/Griffin Trade Paperback).
"Our results suggest that indeed, moderate activity, even when started in a woman's postmenopausal years, can cut her risk of breast cancer by about 20 percent, suggesting that physical inactivity may be a modifiable breast-cancer risk factor in older women."
In addition, the researchers found that regular exercise also causes a similar reduction in overall breast-cancer incidence among women considered to be at highest risk for the disease, such as those with a strong family history of breast cancer, those who've never had children and those who take combination estrogen/progestin hormone-replacement therapy.
"The good news is that even though HRT increases the risk of breast cancer, exercise is something women can do to lower this risk if they choose to continue taking HRT to manage the symptoms of menopause or to prevent osteoporosis," McTiernan said.