British Medical Journal — MedicalXPress, 6 September 2022
Boosting physical activity levels and curbing sitting time are highly likely to lower breast cancer risk, finds research published online in the British Journal of Sports Medicine. The Mendelian randomisation study used genetic variants as proxies for lifelong physical activity levels and sedentary behaviour to obtain genetic evidence in support of a causal relationship. The researchers included data from 130,957 women of European ancestry participating in 76 studies under the Breast Cancer Association Consortium (BCAC). Analysis of the data showed that a higher overall level of genetically predicted physical activity was associated with a 41% lower risk of invasive breast cancer, largely irrespective of menopausal status, tumour type, stage or grade. Similarly, genetically predicted vigorous physical activity on three or more days of the week was associated with a 38% lower risk of breast cancer compared with no vigorous activity.
Crucially, a greater level of genetically predicted sitting time was associated with a 104% higher risk of triple-negative breast cancer — consistent across hormone-negative tumour types. There are plausible biological explanations, with evidence indicating numerous causal pathways between physical activity and breast cancer risk, such as overweight/obesity, disordered metabolism, sex hormones and inflammation. “Increasing physical activity and reducing sedentary time are already recommended for cancer prevention. Our study adds further evidence that such behavioural changes are likely to lower the incidence of future breast cancer rates. 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,” the researchers concluded.