Here’s another reason to get active—as if we really needed more. A review of research found that physically active women are 25 percent less likely to get breast cancer, with certain groups more likely to see benefits than others.

The type of activity undertaken, a woman’s body mass index (BMI) and time in life help determine how protective the activity is against the disease, according to the study published online ahead of print in the British Journal of Sports Medicine.

Lean women who play sports or undertake other physical activities have the lowest risk of breast cancer, especially if they are past menopause. The researchers analysed 62 studies looking at the impact of physical activity on breast cancer risk. They then examined the findings to determine how breast cancer risk appeared to be affected by type of activity, intensity of activity, when in life the activity was performed and other factors.

The review found that the most physically active women were least likely to get breast cancer. All types of activity reduced breast cancer risk but recreational exercise reduced it more than physical activity related to a job or looking after the house. Moderate and vigorous activity had equal benefits.

Physical activity reduced breast cancer risk in all women except the obese and had the greatest impact in lean women (BMI < 22). Women who were mothers, had no family history of breast cancer, were not white and had estrogen receptor negative tumours also had a reduced risk of breast cancer.

The authors said the way in which physical exercise protected against breast cancer is likely complex and may involve the effects of sex hormones, insulin-related factors, the immune system and other hormone and cellular pathways.

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