Over 60 studies have been published that have examined the relationship between physical activity and breast-cancer risk. Although the majority of studies indicate that physically-active women have a lower risk of developing breast cancer than inactive women, the amount of risk reduction varies widely (from 20 percent to 80 percent). Most evidence suggests that physical activity reduces breast-cancer risk in both premenopausal and postmenopausal women. Women who increase their physical activity after menopause may also experience a reduced risk compared with inactive women.
High levels of moderate to vigorous physical activity during adolescence may be especially protective. For example, a recent prospective study of the activity levels of adolescent girls in relation to their subsequent risk of benign breast disease (a risk factor for later development of breast cancer) found that adolescent girls who — as young women — walked the most were at the lowest risk. The association between adolescent physical activity and breast cancer risk was also examined among women enrolled in the Nurses’ Health Study II. An inverse association was observed between physical activity at ages 14–22 and premenopausal — but not postmenopausal — breast cancer. The association was strongest for women
Awareness may have played a role in the findings of the association between diet intake and breast cancer among Polish women who were ranked according to their level of regular physical activity. The results suggested that a higher intake of vegetables and fruits may be associated with a decreased risk of breast cancer among women who were ranked in either the lowest or highest quartiles of lifetime physical activity. In addition, there was a positive association for sweets and dessert intake among women in the lowest quartile of PA. These findings could be interpreted to suggest that a high intake of antioxidant-rich foods could confer protection in the presence of either a sedentary or extremely active lifestyle. Furthermore, the high intake of sweets in those ranked as least active could be associated with a higher risk for breast cancer. One additional study found that physical activity performed either before or after cancer diagnosis was related to reduced mortality risk for both breast and colorectal cancer survivors.