Breast size and exercise – how do they affect breast cancer mortality?

This paper studied how exercise and breast size were associated with breast cancer mortality. 

Studies have shown that exercise reduces breast cancer mortality (death). However, it does not examine in detail the intensity and type of exercise. Additionally, it is not known if this is the case for all women. Breast size also affects breast cancer mortality. Since exercise affects breast size, this study analyzes both exercise and breast size to identify predictors of breast cancer mortality.

79,124 female walkers and runners were recruited for the study. The intensity of their exercise was measured as metabolic equivalent hours per week (uses the level of energy typically used per hour for walking or running to evaluate energy used). The minimum exercise recommendation for health is more than 12.5 metabolic equivalent hours per week (undertaking exercise that is equal to at least 12.5 hours walking or running per week). Height, weight, diet, bra cup size and family history were reported. After approximately 10 years, breast cancer mortality (number of deaths due to breast cancer) was found.

The results found that the decline in breast cancer mortality in women who met or exceeded the exercise recommendation was not different for walking and running. The risk was similar for those with 7.5-12.5 metabolic equivalent hours per week and those with more than 12.5 metabolic equivalent hours per week.

The risk for breast cancer mortality was 41.5% lower for those with 7.5 or more metabolic equivalent hours per week compared to those with less than 7.5 metabolic equivalent hours per week.  After considering breast cup size and body mass index (BMI), participants with 7.5 or more metabolic equivalent hours per week had a 38.5% decreased risk of breast cancer mortality.

There was a 57.9% greater risk of breast cancer mortality with every increase in cup size. When BMI was taken into consideration, this risk increased to 70.4%. In addition, the metabolic equivalent hours per week ran or walked did not significantly affect this risk. 

The authors concluded that breast cancer mortality decreased with smaller breast volume and meeting exercise recommendations. 

Patient information was self-reported.