An ambitious study designed to demonstrate causation has revealed that increasing physical activity levels and decreasing time spent sitting could reduce breast cancer risks.
Mendelian randomization study results were consistent across all stages and types of breast cancer, suggesting exercise as an effective means to ward off breast cancer.
Mendelian randomization is a method that utilizes genetic variants as surrogates of specific risk factors to provide genetic evidence supporting causal relationships, in this instance between lifelong sedentary behavior and levels of physical activity.
Studies involving observational research have found an association between physical inactivity and sedentary behavior and breast cancer risk and higher risks, but don’t establish causality.
Mendelian randomization was utilized to assess whether long-term sitting and physical activity may be causally associated with risk of breast cancer among different types of tumors.
Data was included from 130,957 women; of these women 69 838 had locally spread invasive tumors; 6667 had in situ tumors that hadn’t spread; and 54 452 served as comparison groups.
Data from previously published studies was used to genetically predict how physically inactive or active each of the participants in this study were.
Estimating the overall risk of breast cancer involved taking into account whether women were menopausal; type of cancer (positive for progesterone, estrogen or HER-2 hormones, negative/positive all three hormones or any combination), stage of spread (extent and size of tumor spread) and grade (degree of tumor cell abnormality).
These groups included 23,999 peri/premenopausal women with breast cancer that was invasive and 17,686 who did not; as well as 45,839 postmenopausal women who had the disease and 36,766 who did not.
46,528 tumors were estrogen receptor-positive with 11,246 controls; 34,891 tumors were progesterone receptor positive with 16,432 controls; 6945 were HER2 positive and 33214 controls had them as well; 1974 cases were triple positive; 4964 cases were triple negative.
There were 42,223 cases of invasive lobular/ductal cancer with 8795 controls and 3510 cases of ductal carcinoma in situ; 17,583 cancers that were stage 1, 15,992 that were stage 2 and 4553 that were stages 3-4; 34 647 tumors that displayed moderately abnormal cell activity while 16, 432 cases represented highly abnormal cell behavior.
Data analysis demonstrated that increasing genetically predicted physical activity levels was linked with a 41% lower risk of invasive breast cancer risk – regardless of tumor type, grade, stage or menopausal status.
Genetically predicted physical activity of vigorous-intensity for three or more days per week has been associated with a 38% lower breast cancer risk compared to no vigorous activity at all, and was consistently found among most case groups.
Genetically predicted sitting time levels have also been linked with an increased triple-negative breast cancer risk of 104%; similar results were found across other hormone-negative tumors.
Although increasing physical activity and reducing sedentary time are already recommended as ways to lower cancer risks, this study’s results provide clear evidence that spending less time sitting and engaging in more physical activities will indeed lower breast cancer risks.
