DOCTOR'S VIEW ARCHIVE
Exercise Improves Breast Cancer Survival
Walking just one or more hours per week or undertaking a comparable amount of physical activity may improve survival in women who have breast cancer, according to a study of over 2,900 women with breast cancer.
Doctors at Harvard Medical School studied female registered nurses who were enrolled in the Nurses' Health Study and who were diagnosed with breast cancer in stages I-III between 1984 and 1998. The researchers looked at the women's responses to questions concerning their overall levels of physical activity, measured as metabolic equivalent task (MET) hours. Three MET-hours is equivalent to walking at average pace of 2 to 2.9 mph for 1 hour. The surviving women were followed in the study until June 2002.
When compared with women who took part in less than three MET-hours of activity per week, those who engaged in 3 to 8.9 MET-hours per week had a 20% lower death rate. For 9 to 14.9 MET-hours of physical activity, the risk of death was 50% lower. Higher levels of activity (15-23.9 and 24+ MET-hours) resulted in decreases in death rate of 44% and 40%, respectively, when compared with inactive women.
The effect of prolonged survival with exercise was most pronounced in women whose breast tumors were hormone-responsive (meaning that the tumors express estrogen and/or progesterone receptors and can be stimulated to grow by one or both of these hormones). While the reasons for the increase in survival with exercise remain unclear, doctors hypothesize that lower levels of potentially tumor growth-stimulating ovarian hormones, such as estrogen, in the bloodstream may be one reason. Physical activity has already been shown to result in lower levels of circulating ovarian hormones.
This study suggests that women with breast cancer who are able to exercise may improve their chances of survival if they participate in a moderate amount of physical activity.
Reference: JAMA. 2005;293:2479-2486.
Last Editorial Review: 5/25/2005
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