The results of the new study suggest that greater overall physical activity levels, greater vigorous activity, and lower sedentary time are likely to reduce breast cancer risk, said the authors.
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“Increasing physical activity and reducing sedentary time are already recommended for cancer prevention. Our study adds further evidence that such behavioral changes are likely to lower the incidence of future breast cancer rates,” Suzanne C. Dixon-Suen, PhD, of Cancer Council Victoria, Melbourne, and colleagues reported on behalf of the Breast Cancer Association Consortium (BCAC).
The findings were published online in the British Journal of Sports Medicine.
The investigators used individual-level BCAC case-control data and performed two-sample Mendelian randomization – a study method that assesses causality by using genetic variants as proxies for particular risk factors. In this case, genetic variants were used as proxies for lifelong physical activity levels and sedentary behaviors.
“[Genetic] instruments were single-nucleotide polymorphisms (SNPs) associated in UK Biobank [genomewide association studies] with overall physical activity (all movement), vigorous physical activity, or sedentary time” as assessed by a wrist-worn accelerometer.
Patients with greater genetic predisposition to higher overall activity levels had a 41% lower overall breast cancer risk (odds ratio, 0.59), the team reported. Genetically predicted vigorous activity was associated with a 38% lower risk of premenopausal and perimenopausal breast cancer (OR, 0.62 for 3 or more days vs. 0 days of self-reported days per week).
Conversely, greater genetically predicted sedentary time was associated with a 77% higher risk of hormone receptor–negative breast cancer risk (OR, 1.77), including triple-negative breast cancer, for which the risk was 104% higher (OR, 2.04).
The findings were generally consistent across disease types and stages, and were unchanged after factoring in “the production by a single gene of two or more apparently unrelated effects (pleiotropy), such as smoking and overweight, for example,” according to a press release from the journal.
The investigators included data from 130,957 women of European ancestry. Of those, 69,838 had invasive disease, 6,667 had in situ tumors, and 54,452 were controls without breast cancer. The case-control groups included 23,999 pre-/perimenopausal women with invasive breast cancer and 17,686 women without, and 45,839 postmenopausal women with breast cancer and 36,766 without.
A number of plausible biological explanations for the findings exist, the authors noted, adding that convincing evidence suggests there are causal pathways between physical activity and breast cancer risk, including overweight and obesity, disordered metabolism, sex hormones, and inflammation.
Furthermore, the researchers reported, “mechanisms linking sedentary time and cancer are likely to at least partially overlap with those underpinning the physical activity relationship.”
For the future, they suggested that “[a] stronger cancer-control focus on physical activity and sedentary time as modifiable cancer risk factors is warranted, given the heavy burden of disease attributed to the most common cancer in women.”
This study was funded by multiple international sources. Dr. Dixon-Suen reported no relevant financial relationships. Several coauthors disclosed relationships with industry.
A version of this article first appeared on Medscape.com.