Practising sport for more than an hour a day reduces the risk of contracting breast cancer, and this applies to women of any age and any weight, and also unaffected by geographical location, according to research presented to the 9th European Breast Cancer Conference (EBCC-9). Compared with the least active women, those with the highest level of physical activity reduced their risk of breast cancer by 12%, researchers say.
Professor Mathieu Boniol, Research Director at the International Prevention Research Institute, Lyon, France, reported to a press conference the results of a meta-analysis [presumably this is the largest study to date?] of 37 studies published between 1987 and 2013, representing over four million women. "These are all the studies looking at the relationship between physical exercise and breast cancer risk that have been published to date, so we are confident that the results of our analysis are robust," he said.
Although the results varied according to tumour type, the overall message was encouraging, the researchers say. However, in women taking hormone replacement therapy (HRT), the protective effect of exercise seemed to be cancelled out. But increased awareness of the side effects of HRT means that its use is decreasing in a number of countries, and this means that the beneficial effects of activity will most likely grow in the years to come. "Whether or not this will be the case is an interesting question and deserves to be followed up at a later date," Prof Boniol said.
Physical activity is known to have a protective role in other cancers, as well as in disorders such as cardiovascular disease. Although the mechanisms for its effect are unclear, the results are largely independent of body mass index (BMI), so the effect must be due to more than weight control. And the age at which sporting activity starts also appears to be immaterial; the researchers found no indication that breast cancer risk would decrease only when physical activity started at a young age.
"Adding breast cancer, including its aggressive types, to the list of diseases that can be prevented by physical activity should encourage the development of cities that foster sport by becoming bike and walk-friendly, the creation of new sports facilities, and the promotion of exercise through education campaigns," said Prof Boniol. "This is a low cost, simple strategy to reduce the risk of a disease that currently has a very high cost, both to healthcare systems and to patients and their families. It is good news both for individuals and for policy makers."
Dr Hilary Dobson, chair of EBCC-9's national organising committee and who is Clinical Lead of the West of Scotland Breast Screening Service and the Lead Clinician of the West of Scotland Cancer Advisory Network (WoSCAN), commented: "These findings are important for all women, irrespective of their age and weight. Whilst the mechanism for the potentially protective effect of physical activity remains unclear, the analysis, which is presented here, provides women with a real impetus to increase their physical activity by even modest increments. This review seems to be telling us that the resultant improvements in breast health can now be added to the other established health benefits of physical activity."