It seems that postmenopausal women engaged in various dynamic physical activity are at much lower risk of breast cancer.
The advantageous effect was most definite for oestrogen receptor positive/progesterone receptor negative tumors, which are in general more aggressive.
"It looks like next confirmation to the fact that physical activity will help decrease the risk of breast carcinoma and may play other important roles in addition to effects on cardiovascular health," said Dr Jay Brooks, chairman of haematology/oncology at Ochsner Health System in Baton Rouge.
Whereas overweight and obesity constitute risk factors for breast cancer, the results of the studies also indicate that additional mechanisms may be involved in encouraging the growth of tumors.
Physical activity reduces risk
The correlation between physical activity and a lower risk of breast cancer is not a new one. Previous research has proven that vigorous exercises can decrease the risk for the disease among women of all ages.
But due to the fact that breast cancer is such a diverse disease, there may be various risk factors, depending on different tumor characteristics, such as oestrogen receptor and progesterone receptor status. Receptor status refers to whether these hormones bind to the surface of the tumor.
According to the scientists, there were only three tiny studies that have analyzed the connection between exercising and postmenopausal breast cancer defined by receptor status.
The latest research, known as the Iowa Women’s Health Study, is the largest research to cross-classify oestrogen receptor and progesterone receptor status, explained Dr James Cerhan, senior author of the study and professor of epidemiology at the Mayo Clinic College of Medicine in Rochester, Minnesota. The results of this study are published in the December 11/25 issue of Archives of Internal Medicine.
Cerhan and his team observed 41 836 postmenopausal women who were between 55 and 69 years of age in 1986. The participants had to fill in a 16-page questionnaire at the outset of the research about their recreational physical activity and then were monitored for eighteen years.
14 per cent decreased the risk of breast cancer
Women who engage in practicing a lot of sports were at a fourteen per cent lower risk of breast cancer than women who took part in low levels of activity. After the scientists adjusted for body mass index (BMI, a ratio of weight to height), they discovered that women with high levels of physical activity were at a nine percent lower risk of breast cancer.
"Physical activity protected from developing breast cancer, however when we adjusted for BMI, it weakened the correlation," Cerhan said.
This would suggest that something apart from physical activity contributed to the protective effect.
Hormone receptors involved
The findings were even more remarkable when hormone receptor status was taken under consideration. Women with high levels of physical activity were at a 33 per cent lower risk of experiencing oestrogen receptor-positive tumors.
High levels of physical activity included energetic exercises such as jogging, swimming or racket sports two or even more times weekly or moderate activity such as bowling, golf, gardening or walking at least five times weekly. Average physical activity was vigorous activity once a week or moderate activity one to four times a week.
Being overweight is a common risk factor for breast cancer, due to the fact that body fat produces oestrogen signalling some tumors to grow.
"This is one more reason to be physically active. But I believe that much of the information is for medical experts trying to think about the mechanisms of breast cancer," Cerhan added.
