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THURSDAY, March 20, 2014 (HealthDay News) — Getting more than an hour of physical activity each day can reduce women’s risk for breast cancer, new research suggests.

Although the type of tumor a woman has affects how much exercise could help, a new review of 37 studies found regular physical activity is beneficial for women of all ages and sizes.

“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,” Mathieu Boniol, research director at the International Prevention Research Institute in Lyon, France, said in a news release from the European Cancer Organization.

The researchers analyzed data involving more than 4 million women. When compared with the women who got the least amount of physical activity, those who were most active reduced their risk for breast cancer by 12 percent, the review showed.

The research, which was to be presented Thursday at the European Breast Cancer Conference in Glasgow, Scotland, revealed that exercise reduced women’s risk for breast cancer regardless of their age or body mass index (a measurement based on height and weight). The researchers concluded the benefits of exercise are not due to weight loss alone or simply being active from a young age.

“These findings are important for all women, irrespective of their age and weight,” Dr. Hilary Dobson, chair of the European Breast Cancer Conference’s national organizing committee, said in the news release. “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.”

Physical activity has already been shown to help protect against other forms of cancer and heart disease, the authors noted.

“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,” Boniol said.

“This is a low-cost, simple strategy to reduce the risk of a disease that currently has a very high cost, both to health care systems and to patients and their families. It is good news both for individuals and for policy makers,” Boniol added.

The review authors noted that hormone replacement therapy counters the protective effect of exercise. They pointed out a growing number of women will likely still benefit from more physical activity since public awareness of the possible side effects of HRT has resulted in a significant drop in its use.

Research presented at medical meetings should be viewed as preliminary until published in a peer-reviewed journal.

More information

The U.S. National Cancer Institute provides more information on physical activity and cancer.