However, this research suggests that only some groups of women will see the full protective effect. The relative risk of breast cancer is known to be affected by a woman's physical activity levels and her body mass (specifically fat mass). This study, which analysed 62 papers that focused on physical activity and its association with breast cancer, showed that it is lean women who play sports and who are physically active in their spare time, who receive the greatest protective effect, particularly if they are menopausal.
Although all activity types can lower the relative risk of breast cancer, it is the most physically active women who are the least likely to develop the disease.
Post-menopausal women who had been very active during their lives were found to have the lowest breast cancer risk, and post-menopausal activity had a greater impact than activity performed earlier in life. Among obese women, physical activity did not reduce risk, whereas the greatest reduction in risk was seen in lean women. A lower breast cancer risk was also noted in women who were mothers, did not have a family history of the disease, were not white, and had oestrogen receptor negative tumours.
