Women who have children before the age of 30 have less risk of developing breast cancer than women who become pregnant later in life or who never have children. Using mice for their research, doctors compared the number of mammary or breast cells (cells that turn into breast tissue) found in mice who have been

pregnant verses mice who have never been pregnant. The results showed that mice who had previously been pregnant, especially at an early age, had half the number of mammary cells than mice who had never been pregnant. This reduced number of mammary cells then helps protect against the development of breast cancer, but the reasons for this reduced risk is still uncertain.

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