Physical Activity Cuts Breast Cancer (Death) Risk - New Studies
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Some new studies suggest physical activity may help prevent breast cancer or even death from the disease.
Christine M. Friedenreich published an article in the June 2010 issue of Seminars in Oncology saying that women who were most physically active were at least 25 percent less likely to be diagnosed with breast cancer compared to those who were least active.
The finding was based on data from 73 studies which were published before March 2010.
Friedenreich said the majority of studies showed a dose-response effect. Among all types of activity, recreational and household activities were most effective in reducing the risk of breast cancer. Physical activity that was of at least moderate intensity and sustained over a lifetime was also most strongly associated with reduced risk of the disease.
The effect of physical activity varies from woman to woman. A stronger effect was found in women who had a normal body weight, who did not have a family history of breast cancer and who had given birth.
The protective effect of physical activity against breast cancer was observed in all groups of women even though a particularly strong effect was observed among non-Caucasian women.
Among other things, physical activity has been known to reduce the hormones that promote the growth of breast cancer cells.
A trial led by Christine M. Friedenreich and colleagues from Alberta Health Services and published in the March 20 2010 issue of Journal of Clinical Oncology confirmed that an aerobic exercise intervention changed hormone profiles in subjects, which are linked with a lower risk for postmenopausal breast cancer.
The trial enrolled 320 postmenopausal, sedentary women aged 50 to 74 years. Of the participants, 160 were randomly assigned to a 1-year aerobic exercise of 225 minutes per week and the other 160 participants were required to maintain their usual levels of activity.
During the 1-year trial, estrone, estradiol, androstenedione and testosterone were measured at baseline, 6 months, and 12 months.
At 12 months, estradiol was reduced by 7 percent, free estradiol dropped by 9 percent and SHBG was increased 4 percent in the physical exercise group compared to the control group.
In contrast, no difference was observed between the two groups in estrone, androstenedione and testosterone levels.
Another study published in the May 2010 issue of Nutrition and Cancer also confirmed that all ethnic groups of women including Caucasian-Americans, African-Americans, Hispanic-Americans, Tunisian-Arabs, and Polish-Caucasians were 35 percent less likely to develop breast cancer if they engaged in physical activity for more than 30 minutes per week.
The study led by Luke D. Ratnasinghe and colleagues from Cytonix and BioServe Biotechnologies in Beltsville, Maryland involved 1,463 cases of breast cancer and 4,862 controls.
The study also found women who reported physical activity once per week or more were 50 percent less likely to acquire breast cancer compared to those who reported physical activity less than once per week.
However, more sessions of physical activity like more than 3 times per week were not associated with any additional reduced risk while a longer time spent in each session of physical activity was significantly associated with reduced risk of breast cancer.
The researchers concluded that physical activity may reduce risk of breast cancer regardless of race, weight status or family history of this malignancy.
Studies have also associated physical activity with reduced mortality from breast cancer.
A recent study published in the April 22, 2010 issue of Medical Oncology shows post-diagnosis physical activity reduced breast mortality by 34 percent and physical activity in general reduced mortality by 41 percent.
The study led by Ibrahim E. M. and Al-Homaidh A. from International Medical Center in Kingdom of Saudi Arabia involved 12,108 patients with breast cancer.
Melinda L. Irwin explains in a report published recently in Exercise and Life Sciences that "The beneficial effects of PA may be mediated through a reduction in body fat and beneficial changes in metabolic (e.g., insulin) and sex hormones (e.g., androgens and estrogens), growth factors (IGF-I and associated binding proteins, e.g., IGFBP-3), adipokines (e.g., leptin, adiponectin), and/or inflammation (e.g., CRP)."
Another possibility is that physical activity protects against breast cancer by helping blood circulation, which can make sure sufficient amounts of oxygen is pumped to where it is needed. Cancer cells can't grow well when oxygen is present.
More reports on breast cancer prevention will be published here in the National Breast Cancer Awareness Month to help readers better understand the risk of disease and how to prevent it.
By David Liu
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