A large new study found that when postmenopausal women stop physical activity, their odds of developing breast cancer rise. But the study also found that breast cancer risk drops surprisingly rapidly after exercise starts.

The team of lead author and epidemiologist Agnes Fournier at the Institut Gustave Roussy in France followed 59,308 postmenopausal women for an average of 8.5 years. More than 2,100 were ultimately found to have primary invasive breast cancer. But women who, in the prior four years, had exercised regularly— at least four hours of walking or cycling per week— were 10 percent less likely to be diagnosed with breast cancer than those exercising less.

“The literature regarding the protective effects of recreational physical activity for postmenopausal breast cancer is rather consistent with decreasing breast cancer risk associated with increasing levels of physical activity,” Fournier told Bioscience Technology by email.

“However, we wanted to disentangle the effect of recent physical activity (within the previous four years) from the effect of past physical activity (five to nine years earlier). Our most surprising finding was that recreational/transport physical activity (including walking, cycling and engaging in other sports), even of modest intensity, seemed to have a rapid impact on breast cancer risk. It was quite rapidly associated with a decrease in breast cancer risk, which was however attenuated when activity stops.”

Independent of other factors

The breast cancer reduction link with regular exercise was independent of weight, body fat, waist circumference, and exercise levels. Yet, most recreational physical activity, even of modest intensity, had a rapid impact on breast cancer risk.

The effect quickly vanished when exercise stopped.  But even walking a mere 30 minutes a day was beneficial. 

Cause and effect wasn’t proven. It is unknown exactly why there were decreased risks— healthier lifestyles could have played a role.

But either way, exercise was key.

The future

In the future, the group will continue research on the link between physical activity and breast cancer. “How does the level, type, or duration of physical activity influence cancer risk and prognosis?” is one of the “provocative questions” Fournier said was identified by the National Cancer Institute.

“Studies are indeed needed to determine what features or types of physical activity are most important in achieving the benefits of physical activity regarding the risk of cancer, and what is the mechanism underlying these effects,” she said. “The follow-up of [our] 100, 000 “E3N” women, born between 1925 and 1950, is continuing. We will thus be able to perform specific studies in elderly women in a couple of years.”

Fournier added that her team is building up a “complimentary cohort” composed of E3N participant’s children, grandchildren, and spouses (the children’s fathers). “We will be able to investigate the influence of environmental, genetic, and epigenetic factors during different periods of life on disease risk and progression. This will include the influence of physical activity on the risk of cancer,” she said.

Another recent study

In another recent study, a group at the University of New Mexico Health Sciences Center zeroed in on one potential reason exercise reduces breast cancer risk: irisin, a myokine linked to exercise and lean body mass, which is thought to favorably alter metabolism. Different doses of irisin were added to dishes of malignant and non-malignant breast epithelial cells. Irisin significantly decreased cell number, migration, and viability in malignant cells. It did not affect non-malignant cells.

Furthermore, irisin enhanced the cytotoxic effect of the cancer drug doxorubicin when added to the malignant cell type. This effect was not seen in the non-malignant cells. The team speculated irisin may aid breast cancer prevention and treatment via an anti-inflammatory response, an induction of cell suicide or enhanced tumor sensitivity to common antineoplastic agents, like doxorubicin.