What is the relationship between physical activity and the risk of breast cancer?

The relationship between physical activity and the incidence of breast cancer has been studied extensively, with many studies worldwide. Most studies indicate that physically active women have a lower risk of inactive women with breast cancer; however, the amount of risk reduction achieved through physical activity is very variable (from 20 to 80 percent). Although most evidence is that physical activity reduces the risk of breast cancer in premenopausal and postmenopausal women, high levels of moderate and vigorous physical activity during adolescence may be especially protective. Although a lifetime of regular strenuous activity is thought to be of greatest benefit, women who increase their physical activity after menopause may also experience reduced compared with inactive women risk. Is a reduced risk of breast cancer with increasing frequency and duration of the physical activity. Most studies suggest that 30 to 60 minutes per day of moderate to high intensity physical activity are associated with a reduced risk of breast cancer.
Researchers have proposed various biological mechanisms to explain the relationship between physical activity and the development of breast cancer. Physical activity can prevent tumor development by reducing hormone levels, particularly in pre-menopausal women; reducing insulin levels and insulin-like growth factor-I (IGF-I), enhancing the immune response; and help with weight maintenance to prevent body mass and excess fat in the body.

Source: National Cancer Institute.