How exactly can breast feeding lower the risk of breast cancer?

Hormonal changes: Breast feeding has been shown to be a factor that is associated with a lower risk of breast cancer the cause if this effect is most likely hormonal as estrogen levels are one of the factors that increase the risk of breast cancer.

Number of Periods: Epidemiological studies have shown multiple factors associated with lower risks for breast cancer in women who have had fewer periods (late puberty, early menopause, pregnancy esp@early age, breastfeeding). We think this has to do with estrogen exposure but its probably not that simple.