The two important questions to answer regarding breast cancer and exercise are:
Does regular exercise reduce the risk of developing breast cancer?
Does regular exercise improve the chances of survival during treatment for breast cancer.
The answer is yes on both accounts. It is important to note the difference in exercise intensity and exercise duration in understanding the risk reduction benefit of exercise. Duration and frequency may be more important than intensity in causing risk reduction.
Prevention.
Physical activity has been proposed as a modifiable risk factor for invasive breast carcinoma because of its potential effects on circulating sex hormones, such as estrogen, which is associated with higher levels with higher body fat and breast cancer. Researchers at the University of Southern California Keck School of Medicine, Los Angeles, California interviewed 567 women with a recent diagnosis of non-invasive breast cancer (breast carcinoma in situ), which is associated with an increase risk of invasive breast cancer. They also interviewed 616 women without a breast cancer diagnosis. Among other factors, the researchers compared the exercise habits of women with non-invasive breast cancer to those who did not have breast cancer. The study found that among women without a family history of breast cancer, who exercised, there was a 30% decreased risk of non-invasive breast cancer compared to women who did not exercise. The study entitled Lifetime recreational exercise activity and risk of breast carcinoma in situ was published in Cancer in 2003.
In another study, 93676 women were enrolled and 74171 were chosen for evaluation in the Women’s Health Initiative Observational Study (WHIOS) at 40 clinical centers between October 1993 and December 1998. The women were characterized by age 50 to 79 years, they were postmenopausal, and free of serious health conditions that might reduce survival during the following 3 years. Women were excluded if they reported a history of breast cancer or had missing physical activity data before the test study began. Exercise was characterized as follows: the women were asked if they usually exercised enough to work up a sweat greater than or equal to three times per week at ages 18, 35, and 50 years. Current (baseline) walking for greater than or equal to 10 minutes and participation in leisure-time activities were categorized by frequency, duration, and intensity. Exercise was reported according to physical activity categories of MET-hours per week. A rating of 1 MET is resting level. A rating of 3 MET-hours is equivalent to walking an average pace of 2 to 2.9 mph for one hour. The main outcome measure was the association of incidence of breast cancer with measures of physical activity.
Compared with no current physical activity, the breast cancer risk was reduced as follows:
Breast Cancer Risk Reduction MET Hrs per week
18% ………………………….. 5.1-10
11% ………………………….. 10.1-20
17% ………………………….. 20.1-40
22% ………………………….. >40
Hours of current moderate or strenuous physical activity was not significantly related to risk of breast cancer, although the highest duration category, greater than 7 MET-hours per week, compared with 0 MET hours per week showed a significant reduction in risk. The study entitled Past recreational physical activity and risk of breast cancer was published in Clinical Journal of Sports Medicine in 2003 and concluded that increased physical activity was associated with a lower risk of breast cancer in postmenopausal American women. One hour per day of moderate or strenuous activity provided the most benefit.
Treatment
There is evidence to suggest that treatment of breast cancer with chemotherapy can cause negative metabolic changes in skeletal muscle. Women undergoing treatment for breast cancer with certain chemotherapeutic agents can experience declines in lean body mass, declines in muscle strength, and increase in body weight, which can lead to the development or recurrence of breast cancer. Researchers at Harvard Medical School, Boston, Massachusetts studied 2987 female nurses in a study known as the Nurses’ Health Study who were diagnosed with stage I, II, or III breast cancer between 1984 and 1998 and who were followed up until death or June 2002, whichever came first. Breast cancer mortality risk was compared to physical activity categories of MET-hours per week. A rating of 1 MET is resting level. A rating of 3 MET-hours is equivalent to walking an average pace of 2 to 2.9 mph for one hour. Breast cancer patients who walk or do other kinds of moderate exercise for three to five hours a week were found to be about 50 percent less likely to die from the disease when compared to sedentary women.
The greatest benefit of exercise against breast cancer occurred in women who exercised the equivalent of walking 3 to 5 hours per week at an average pace. Greater energy expenditure did not appear to correlate with a greater benefit from exercise. The study entitled Physical activity and survival after breast cancer diagnosis was published in JAMA in 2005.
Sources:
Holmes MD, Chen WY, Feskanich D, Kroenke CH, Colditz GA. Physical activity and survival after breast cancer diagnosis. JAMA. 2005 May 25;293(20):2479-86.
Macera CA. Past recreational physical activity and risk of breast cancer. Clin J Sport Med. 2005 Mar;15(2):115-6.
Patel AV, Press MF, Meeske K, Calle EE, Bernstein L. Lifetime recreational exercise activity and risk of breast carcinoma in situ. Cancer. 2003 Nov 15;98(10):2161-9.
Meric F, Bernstam EV, Mirza NQ, Hunt KK, Ames FC, Ross MI, Kuerer HM, Pollock RE, Musen MA, Singletary SE. Breast cancer on the world wide web: cross sectional survey of quality of information and popularity of websites. BMJ. 2002 Mar 9;324(7337):577-81.
More Helpful Links:
American Cancer Society (www.cancer.org)
breastcancer.org
National Breast Cancer Foundation (
www.nationalbreastcancer.org)
National Cancer Institute Breast Cancer Page
Wikipedia Alcohol and Cancer
Wikipedia Breast Cancer
