Prolonged Estrogen Exposure

Prolonged, uninterrupted exposure to estrogen can increase breast cancer risk. Breast cell growth—both normal and abnormal—is stimulated by the presence of estrogen. This includes estrogen that your own body produces normally, as well as estrogen you might take as a pill (for example, menopause hormone therapy). The following risk factors for breast cancer are related to prolonged exposure to estrogen without any breaks or interruptions:

• starting menstruation at a young age (more years of the body producing estrogen)
• going through menopause at a late age (more years of the body producing estrogen)
• taking menopause hormone replacement therapy for over five years with estrogen alone, or with estrogen and progesterone (risk increases by 5–40%, but most breast cancers that are diagnosed in women on hormone therapy tend to be very early stage and very treatable)
• never having had a full-term pregnancy
• having a first full-term pregnancy after age 30 (more years of the body producing estrogen without the break from regular cycles)
• being overweight, which increases the production of estrogen outside the ovaries and adds to the overall level of estrogen in the body
• exposure to estrogens in the environment (such as estrogen fed to fatten up beef cattle, or the breakdown products of the pesticide DDT, which mimic the effects of estrogen in the body)
• having more than two alcoholic drinks per week, which can limit your liver's ability to regulate blood estrogen levels