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    Exercise Lowers Breast Cancer Risk

    Moderate Activity Level Cuts Risk of Aggressive Cancer Type by a Third in Older Women

    The Importance of Tumor Type continued...

    All participants were between the ages of 55 and 69 in 1986, when they filled out a 16-page health questionnaire. The women were asked how often and with what intensity they engaged in physical activity.

    High physical activity (9,111 women) was defined as vigorous activity -- such as jogging, swimming, or racket sports -- two or more times each week, or moderate activity -- such as bowling, golf, or walking -- more than four times a week.

    Medium physical activity (10,030 women) was defined as engaging in a vigorous activity once a week or in moderate activity one to four times a week.

    About 17,222 women got less exercise than this and were recorded in the low physical activity group.

    Of the women in the study with breast cancer of a known type, roughly 14% had the progesterone negative, or ER+/PR-, tumors.

    This type of tumor is more aggressive than a progesterone-receptor positive type (ER+/PR+).

    High physical activity was associated with a 34% reduction in the risk of the progesterone-negative tumors, and this risk reduction did not appear to be influenced by body weight, Cerhan says.

    The Impact of Estrogen

    Obesity is a source of estrogen in postmenopausal women, and estrogen also drives the development of estrogen-receptor-sensitive tumors.

    Since the impact of exercise was strongly linked to body weight for ER+/PR+ tumors, but not for ER+/PR- tumors, the researchers suggest that some other mechanism may be involved in the development of tumors.

    "This finding argues against estrogen being the major player for this tumor subtype," Cerhan says.

    But from a public health standpoint, the message is the same.

    Postmenopausal women can lower their overall breast cancer risk by engaging in regular exercise, says breast cancer researcher Anne McTiernan, MD, PhD, of Seattle's Fred Hutchinson Cancer Research Center.

    McTiernan wrote the book Breast Fitness: An Optimal Exercise and Health Plan for Reducing Your Risk of Breast Cancer.

    "Lack of exercise and obesity are thought to account for about a quarter of breast cancer cases," she tells WebMD.

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