For women past childbearing age, a new study finds that a modest amount of exercise — four hours a week of walking or more intensive physical activity such as cycling for just two hours a week — drives down breast cancer risk by roughly 10 percent.
If exercise were a pill, its effectiveness in driving down a woman’s breast cancer risk would occur fairly quickly, the new research says: When women reported at least this modest level of physical activity over the last four years, they were less likely to have developed malignancy in a breast.
But, like a pill, exercise must be continued for the effect to endure: Even if a woman had been physically active earlier in life, when her reported physical activity levels dropped below the equivalent of four hours of weekly walking, her risk of developing breast cancer went back up.
At the same time, the research found that engaging in more physical activity than 12 “metabolic equivalents” per week — either via greater intensity or longer duration of exercise — did not further drive down a woman’s likelihood of breast cancer. The authors suggested that finding such a “dose response” might have required a more detailed record of participants’ energy expenditures than was collected by the European researchers who designed the study.
