Monday November 3, 2008 (foodconsumer.org) -- Physical
activity or exercise may reduce risk of breast cancer in certain groups of women, according
to a review study published in the August, 2008 issue of British Journal of
The study led by Friedenreich CM and Cust AE of Alberta Cancer
Board found that 76 percent of 62 studies showed physical activity was associated
with a reduction of 25 to 30 percent in breast cancer risk/
The researchers found stronger risk reduction in breast
cancer risk among postmenopausal women, women with normal BMI, non-white racial
groups, those with hormone receptor negative tumours, women without a family
history of breast cancer and parous women who engaged in recreational activity,
lifetime or later life activity and vigorous physical activity.
The review was based on 34 case-control and 28 cohort studies
published before September 2007.
Another recent study led by Michael F Leitzmann and
colleagues at the National Cancer Institute found that postmenopausal women
with body mass index lower than 25 kg/m2 engaged in vigorous physical activity
were 23 percent less likely to develop breast cancer.
But no such association was found in
overweight and obese women.
For the study, the researchers followed 32,000 women
enrolled in the Breast Cancer Detection Demonstration Project Follow-up Study
to examine if there was an association between risk of breast cancer and
Physical activity was surveyed by self-administered
questionnaire and postmenopausal breast cancer cases were identified through
self-reports, death certificate and state cancer registries.
During the 11-year follow-up, 1506 new
incident cases of postmenopausal breast cancer were identified.
The researchers found that after adjusting a variety of
risk factors, there was a weak inverse association between total physical
activity and postmenopausal breast cancer.
The study was published in the Oct. 2008 issue of Breast
Most studies are observational, meaning that it not necessarily
that physical activity indeed causes the reduction in breast cancer risk.
However, the possibility is real because there
is evidence that physical activity boots the body's immune response and helps
fight inflammation, which are believed to be important in the fight against
Addition, exercise can also alter levels of
certain hormones including sex hormones and insulin-like growth factors, which
can promote the growth and spread of tumors.
Those who want to know the biological mechanisms whereby
physical activity may influence the risk of breast cancer may read the review
by Friedenreich and Cust.
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