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Study: Modest Exercise May Reduce Breast Cancer Risk (dateline December 20, 2003)

Recreational exercise may reduce the risk of breast cancer in older women, according to new findings by the U.S. government research project, the Women’s Health Initiative. Women over age 50 who engaged in the equivalent of 1.25 to 2.5 hours per week of brisk walking reduced their risk of developing breast cancer by 18%, compared with women who did not exercise. The effect was greatest in women who exercised the most frequency. Researchers say the study highlights the fact that post-menopausal women need not engage in strenuous activity to reduce their risk of breast cancer.

The Women’s Health Initiative was established by the National Institutes of Health in 1991 to address the most common causes of death, disability, and impaired quality of life in post-menopausal women. The project will run a total of 15 years and investigate cardiovascular disease, cancer, and osteoporosis. The main components of the Women’s Health Initiative are three studies: the Hormone Replacement Therapy Trial (HRT), the Dietary Modification Trial (DM), and the Calcium/Vitamin D Supplementation Trial (CaD).

The latest results of the Women’s Health Initiative were published by Anne McTiernan, M.D., Ph.D. of the Fred Hutchinson Cancer Research Center in Seattle, Washington and colleagues; the results appear in the September 10, 2003 issue of the Journal of the American Medical Association.

The current findings are based on an analysis of 74,171 women between the ages of 50 and 79 from 40 U.S. clinical centers who participated in the Women's Health Initiative study from 1993 to 1998. Dr. McTiernan and her team found that women who walked briskly for 1.25 to 2.5 hours per week reduced their risk of breast cancer by 18%. A slightly greater reduction in breast cancer risk was seen in women who engaged in 10 hours of exercise (equivalent to brisk walking) per week. The reduction in breast cancer risk was greatest for women with low body masses but was also seen in women with middle body masses.

Dr. McTiernan and her colleagues conclude that "increased physical activity is associated with reduced risk for breast cancer in postmenopausal women, longer duration provides most benefit, and that such activity need not be strenuous."

The effects of exercise on health have been well documented. In another study published in the same issue of the Journal of the American Medical Association, John M. Jakicic, Ph.D. of the University of Pittsburgh and colleagues found that a combination of diet and exercise over a 12 month period enables women to lose weight and improve cardiovascular fitness. Previous research has shown that exercise can also help older people remain active and disease free for long periods.

Additional Resources and References

  • The reports, "Recreational Physical Activity and the Risk of Breast Cancer in Postmenopausal Women: The Women's Health Initiative Cohort Study," and "Effect of Exercise Duration and Intensity on Weight Loss in Overweight, Sedentary Women," are published in the September 10, 2003 issue of the Journal of the American Medical Association,
  • For information on the Women’s Health Initiative, please visit