Already Linked to Prevention, Exercise Cuts Death from Breast Cancer
Women who are diagnosed with breast cancer often reduce their physical activity. A new study shows that maintaining a moderate level of exercise could save their lives.
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May 29, 2005
In another surprising finding for those interested in the impact of exercise on life-threatening disease, a study published this week in the Journal of the American Medical Association (JAMA) found that women diagnosed with breast cancer who exercised moderately significantly decrease their risk of recurrence and death compared to those who did little or no exercise.
Of particular interest, the protective benefit of working out was seen in women who were overweight. Previous studies have shown that high levels of physical activity can reduce the risk of getting breast cancer by 20% to 40%.
In this study, almost 3,000 women participating in the Nurses’ Health Study diagnosed with breast cancer between 1984 and 1998 replied to questionnaires asking how much physical activity they did per week. Researchers standardized the impact of different types of exercise into metabolic equivalent task (MET) hours per week. One MET hour is the impact on your metabolism of sitting quietly. Walking was the most popular form of exercise reported by women in the study.
Researchers found that the greatest reduction in breast cancer recurrence and death was achieved by women who walked between 3 and 5 hours a week at an average pace (2-3mph). This level of exercise is consistent with current government recommendations for physical activity.
For women who achieved this level of exercise, after ten years the absolute risk of death was reduced by 6% compared to the women who were in the lowest activity level. The resulted a 50% reduction in the relative risk of death compared to the group with the lowest level of physical activity (less than 3 MET hours).
Surprisingly, women who exercised more than 15 MET hours per week did not experience a greater reduction in the risk of death than those exercising between 9 and 15 MET hours per week.
This study is particularly important because previous lifestyle studies of women with breast cancer have found that they reduce physical activity by about two hours per week compared to before they were diagnosed. Because many women are too tired to exercise during active chemotherapy and radiation periods, this period was excluded from the analysis.
Researchers noted that the benefit from exercise was seen particularly in women with tumors overexpressing estrogen receptors and progesterone receptors, suggesting a relationship between exercise and hormone levels impacting breast cancer survival.
“Physical Activity and Survival After Breast Cancer Diagnosis,” Michelle D. Holmes, MD, DrPH, et. al. Journal of the American Medical Association. Vol. 293 No. 20, May 25, 2005
“Weight control and physical activity in cancer prevention,” Bianchini F, Kaaks R, Vainio H. International Agency for Research on Cancer.Obes Rev. 2002 Feb;3(1):5-8
Physical activity levels before and after a diagnosis of breast carcinoma: the Health, Eating, Activity, and Lifestyle (HEAL) study. ML Irwin, et. al. Cancer. 2003 Apr 1;97(7):1746-57.