Exercise and Cancer Risk

Regular exercise provides many health benefits and may decrease cancer risk. Research shows that exercise lowers estrogen levels, which may reduce breast cancer risk.

One study in women with BRCA mutations showed those who were most active during their teens developed breast cancer at a later age than mutation carriers who were sedentary at a young age.  

A 2009 study from the Netherlands examined exercise in 725 BRCA mutation carriers, of which 218 had a diagnosed breast cancer. This study found a  trend, in which women who exercised before age 30 reduced risk of breast cancer, but the result did not reach statistical significance.

A 2015 study looked at the effect of regular exercise on hormone levels and breast tissue in women who were at high risk for breast cancer.  When researchers followed the women’s hormone levels at different stages of their menstrual cycle, they found that: 

• every 100 minutes of exercise reduced estrogen levels by about 4% at the first day of menstrual bleeding (the follicular phase).
• exercise did not affect estrogen levels after ovulation (the luteal phase).
• exercise did not affect levels of progesterone, another hormone that can drive breast cancer growth in either phase.
• For every 100 minutes of exercise, women showed a decrease of approximately 10% in a type of dense breast tissue called “fibroglandular tissue.” Previous studies have shown that increases in the amount of fibroglandular tissue correlate to increased breast cancer risk.

While a reduction in estrogen might reduce the risk of breast cancer developing, it is not yet a certainty. Patients should talk with their health care providers about all the methods they should be using to reduce their risk of developing cancer. In this study, exercise did not lower estrogen levels as much as removing ovaries or taking medications such as tamoxifen or raloxifene

The general consensus from these studies is that a well-balanced diet combined with exercise to maintain appropriate weight seems to decrease cancer incidence among BRCA mutation carriers. Eating a variety of vegetables and maintaining weight stability later in life are both important, as significant weight gain, not actual size, seems to increase the likelihood of being affected with cancer.

Perhaps the best information on lifestyle choices and BRCA-associated cancers will come from a prospective study in Dublin. The study will follow unaffected individuals with BRCA mutations and will track body composition, signs of metabolic syndrome, physical activity, and diet, and will collect blood samples for future use. The benefits of a prospective study include: 1) having pre-diagnosis samples to identify biomarkers of earliest-stage disease, and 2) having an accurate real-time assessment of weight gain, activity, and diet instead of requiring participants to recall these numbers in a future survey.

Visit our Research Study Search Tool to find clinical trials studying exercise and cancer risk.

Updated 12/27/2016