More physical exercise is ‘highly likely’ to lower breast cancer risk, study shows

Boosting physical activity levels and curbing sitting time are “highly likely” to lower the risk of breast cancer, according to new research.

The findings, published online on Tuesday in the British Journal of Sports Medicine, were generally consistent across all types and stages of the disease, prompting the researchers to recommend a stronger focus on exercise as a way of warding off breast cancer.

“These findings are very important for cancer control efforts around the world,” according to one of the authors of the research paper, associate professor Brigid Lynch of the Cancer Epidemiology Division of the Cancer Council Victoria in Australia.

“Cancer control has not to date placed a huge focus on increased physical activity and this research shows we need, literally and metaphorically, to step it up, ” she said.

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The research paper notes observational studies have reported that active lifestyles are associated with lower breast cancer risk but it could not be conclusively determined from these whether activity is the protective factor.

This study provides “strong evidence” that greater levels of physical activity and less sedentary time are likely to reduce breast cancer risk, with results generally consistent across breast cancer subtypes, according to the paper.

The study used Mendelian randomisation, a technique that uses genetic variants as proxies for a particular risk factor, to assess whether lifelong physical activity and sitting time might be causally related to breast cancer risk in general, and specifically to different types of tumour.

They included data from 130,957 women of European ancestry. Of those, 69,838 had tumours that had spread locally and 6,667 had tumours that had not yet done so. The remainder were a comparison group of 54,452 women who did not have breast cancer.

The women were participants in 76 studies under the aegis of the Breast Cancer Association Consortium (BCAC), a forum of investigators interested in the inherited risk of breast cancer.

The researchers then drew on previously published studies to genetically predict how physically active or inactive their own study participants were. The next stage was to estimate overall breast cancer risk, according to whether the women had or had not gone through the menopause; and by the type, stage and grade of cancer.

Analysis of the data showed that a higher overall level of genetically predicted physical activity was associated with a 41 per cent lower risk of invasive breast cancer, and this was largely irrespective of menopausal status, tumour type, stage, or grade.

Genetically predicted vigorous physical activity on three or more days of the week was associated with a 38 per cent lower risk of breast cancer, compared with no self-reported vigorous activity. A greater level of genetically predicted sitting time was associated with a 104 per cent higher risk of triple negative breast cancer.