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Townsend Letter for Doctors and Patients,  Feb-March, 2004  by Tori Hudson

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Exercise and Risk of Breast Cancer in Postmenopausal Women

McTiernan A, Kooperberg C, White E, et al. Recreational physical activity and the risk of breast cancer in postmenopausal women; The Women's Health Initiative Cohort Study. JAMA 2003;290(10):1331-1336.

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Women who have regular exercise have been shown to have a lower risk of breast cancer. However, it is not clear if exercise in postmenopausal women reduces the risk of breast cancer or if life-long exercise is required to incur the breast protective effect. Some studies have suggested that strenuous exercise is required but the intensity and amount are not clearly known. The current study set out to examine the association between recreational physical activity in postmenopausal women and breast cancer incidence.

The study population was 74,171 women who were enrolled in the WHI Observational Study of women aged 50 to 79. The researchers documented 1780 newly diagnosed cases of breast cancer over a mean follow-up of 4.7 years. Compared with women who were less active, menopausal women who had engaged in regular strenuous exercise at age 35 and age 50 had the greatest protective effect against breast cancer. Women who engaged in the equivalent of 1.25 to 2.5 hours per week of brisk walking had an 18% decreased risk of breast cancer compared with women who were inactive. A greater risk reduction was observed in women if they had 10 hours or more per week of something equivalent to brisk walking. The greatest association of exercise and reduced risk was observed for the leanest women although moderately overweight women also had a benefit.

Comments: The results of this study along with other cohort and case-control studies suggest that all practitioners should emphasize regular exercise to both younger and older women as a breast cancer protection strategy. It is also encouraging that merely brisk walking, rather than very strenuous exercise, is adequate to obtain the protective effects of exercise.

There are several mechanisms that may explain the association between physical activity and reduced risk of breast cancer: Reducing body fat and therefore less estrogen from androgen in fat tissue, reduced levels of sex hormone binding globulin and therefore reducing the amount of free estradiol, and reduction of insulin and other growth factors.

by Tori Hudson, ND

Professor, National College of Naturopathic Medicine and Bastyr University Medical Director, A Woman's Time Author, Women's Encyclopedia of Natural Medicine

2067 N.W. Lovejoy * Portland, Oregon 97209 USA

503-222-2322 * womanstime@aol.com

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