Want to reduce your risk of breast cancer? Lace up those shoes and get moving—because exercise has a significant impact.

There is a growing body of evidence to indicate that exercise is crucial to reducing the risk of cancer. Now a new study has put a number on that reduced risk: 41.5 percent.1 That’s right: women who meet the aerobic exercise guidelines spelled out by the Centers for Disease Control and Prevention are 41.5 percent less likely to die of breast cancer than their more sedentary counterparts— even after adjusting for body mass index (BMI).

Here is the kicker: those guidelines are fairly attainable. They recommend two and a half hours of moderate activity (such as brisk walking) or 75 minutes of vigorous activity (such as running) per week.2 To be clear, that is nearly half the risk of breast cancer for less than three hours of effort each week.

The study included 79,124 women (32,872 walkers and 46,252 runners) from the National Walkers’ and Runners’ Health Studies. All the women were cancer-free at the beginning of the study. They were followed for 11 years, during which time 111 women (57 walkers, 54 runners) died from breast cancer. The women reported the distances they ran or walked each week, as well as their bra cup size, body weight, and height.

Running and walking offered the same level of protection. One activity is not better than the other—it is all about energy expenditure. At higher intensities— such as those achieved with running— it simply takes less time to expend the necessary amount of energy. At lower intensities—such as when walking— you will need to spend twice the amount of time for the same results. Choose your intensity level and put in the time, and you are on your way to a significantly reduced risk of breast cancer.

The researchers noted that other than age and menopause, baseline bra cup size was the strongest predictor of breast cancer mortality—the risk of dying from breast cancer increases with bra cup size. Meeting the exercise recommendations decreased the risk of breast cancer, however, regardless of cup size.

What is the relationship between exercise and breast cancer? It might come down to estrogen, which is known to make breast cancer grow. Researchers have theorized that exercise reduces the effects of estrogen on cancer by changing how the body breaks it down. What’s more, exercise can reduce the level of fatty tissue, which secretes estrogen.

The bottom line: exercise can significantly reduce your risk of dying from breast cancer. So, choose your intensity level and get moving! All it takes is a few hours per week to put a major dent in your risk level.


1. Williams PT. Breast cancer mortality vs. exercise and breast size in runners and walkers. PLoS ONE. 2013;8(12): e80616. doi:10.1371/journal.pone.0080616.

2. How much physical activity do adults need? Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/physicalactivity/everyone/guidelines/

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