Previous research has associated inactivity with type 2 diabetes and obesity, but excessive sitting can also increase a woman’s risk of developing breast cancer, claims a new study led by the Cancer Council Victoria in Australia.
Researchers conducted a Mendelian randomisation study, which uses genetic variants as proxies for a specific risk factor, such as lifelong sedentary behaviour.
Within the study of 130,957 women of European ancestry, 69,838 had tumours that had spread locally and 6,667 had tumours which had not spread yet.
They also observed a comparison group of 54,452 women who didn’t have breast cancer.
The researchers drew on studies using data from UK Biobank to explore genetic predisposition to sitting time, physical activity and vigorous physical activity.
This was measured by wrist-worn activity trackers to predict how physically active or inactive participants were.
They also estimated breast cancer risk in relation to menopause, cancer type, stage, and grade.
The findings revealed that a higher overall level of genetically predicted physical activity was linked to a 41 percent lower risk of invasive breast cancer - largely irrespective of menopause status, cancer type, stage, or grade.
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Researchers also found that vigorous physical activity on three or more days of the week led to a 38 percent lower risk of breast cancer, in comparison with no self-reported vigorous activity.
Another notable finding was that a greater level of genetically predicted sitting time was associated with a 104 percent increased risk of triple negative breast cancer.
The results stayed the same when other factors were considered, including smoking and being overweight.
According to the researchers, the findings of the study, which were published in the British Journal of Sports Medicine, applies to all types and stages of breast cancer.
Corresponding author of the study, Professor Brigid Lynch, deputy head of Cancer Epidemiology Division at the Cancer Council Victoria, said: “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.”
She added: “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 claim their study provides strong evidence that physical activity and reduced sitting time can help to lower the risk of breast cancer.
They said: “Mechanisms linking sedentary time and cancer are likely to at least partially overlap with those underpinning the physical activity relationship.”
