Although the underlying mechanisms remain unclear, physical activity has been consistently shown to reduce breast cancer risk in postmenopausal women. More recently, there is evidence that the risk reduction is even seen in premenopausal women . However, it is still unknown whether the reduction in risk of breast cancer is similar in Asian women, as most of the previous studies were performed in Western people. Suzuki and colleagues  have recently conducted a hospital-based, case–control study in Japanese women that considered age and intensity of physical activity. They found that strenuous but not moderate physical activity at the age of 12 years was inversely associated with both pre- and postmenopausal breast cancer risk across estrogen receptor (ER) and progestogen receptor (PR) subtypes (overall odds ratio 0.24; 95% confidence interval 0.14–0.43), and that moderate physical activity in the preceding 5 years was associated with a decrease in risk for postmenopausal breast cancer, but only for ER+ and PR+ tumors, suggesting that the time and optimal intensity of physical activity are involved in the reduction in risk of breast cancer. They also showed that physical activity at the age of 20 years was weakly associated with breast cancer risk, but only when the physical activity was of moderate intensity.
Department of Obstetrics & Gynecology, Hirosaki University, Japan
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