Exercise has a protective effect against invasive breast cancer throughout a woman’s lifetime, new research found.

Six or more hours per week of strenuous recreational activity may reduce the risks of invasive breast cancer by 23 percent, according to researchers from the University of Wisconsin Paul P. Carbone Comprehensive Cancer Center (UWCCC).

The results provide further evidence that for most women physical activity may reduce the risk of invasive breast cancer, the researchers concluded.

 

According to the research of 7,630 women without breast cancer, women who exercised had a reduced risk of developing invasive breast cancer provided they didn’t have a family history of breast cancer. This reduction in risk was apparent whether the physical activity took place early in life, in the postmenopausal years, or in the recent past.

"A woman's hormone levels naturally fluctuate throughout her life, and we have found that exercise likely offers protection against breast cancer regardless of a woman's stage in life," said Brian Sprague, a UWCCC research assistant and lead author of the study. "The take-home message for women should be that it is never too late to begin exercising."

Previous research has linked high levels of estrogen to an increased risk for developing breast cancer. Women who exercise heavily are, in general, older at the time of the first period, and tend to have irregular periods and a shortened estrogen-producing phase, which translates in a lower body exposure to estrogen, the researchers say.

Similarly, postmenopausal women who are physically active have also been shown to have lower levels of estrogen. This reduction may explain why increased physical activity reduces the risk of breast cancer. 

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