If the menstruation starts very early (i.e.) below 12 years and if it continues after 55 years of age, it can be a long period of reproduction which means that the women’s breasts are stimulated by uncontrolled estrogenic stimulation resulting in breast cancer formation. The prolonged periods of reproduction are normally at the age of 30 whereas if it crosses 40 years of age, then they stand a higher chance of developing breast cancer. Prolactin and progesterone are the main hormones during lactation and fertilization. So, the women’s breasts can be protected for a period of 2.5 years from the estrogen. If there are 7 or 8 children, then almost 25 - 30 years of their reproductive period can be free from estrogenic stimulation which means there is very little chance of developing breast cancer. But, in modern days, women having 1 or 2 children don't continue to breastfeed for longer periods. This definitely aggregates the higher incidence of breast cancer.