Breast Cancer & The Environment

Breast Cancer Risk and Protective Factors

The following risk factors may increase the risk of breast cancer:

  • Estrogen
  • Hormone replacement therapy/Hormone therapy
  • Exposure to Radiation
  • Obesity
  • Alcohol
  • Inherited Risk

These risk factors are discussed in the previous sections.

The following protective factors may decrease the risk of breast cancer:

  • Exercise

Exercising four or more hours a week may decrease hormone levels and help lower breast cancer risk. The effect of exercise on breast cancer risk may be greatest in premenopausal women of normal or low weight. Care should be taken to exercise safely, because exercise carries the risk of injury to bones and muscles.

  • Estrogen (decreased exposure)

Decreasing the length of time a woman's breast tissue is exposed to estrogen may help prevent breast cancer. Exposure to estrogen is reduced in the following ways:

  • Pregnancy: Estrogen levels are lower during pregnancy.
  • Breast-feeding: Estrogen levels may remain lower while a woman is breast-feeding.
  • Ovarian ablation: The amount of estrogen made by the body can be greatly reduced by removing one or both ovaries, which make estrogen.
  •  Late menstruation: Beginning to have menstrual periods at age 14 or older decreases the number of years the breast tissue is exposed to estrogen. Exposure to environmental estrogen may lead to early beginning of menstruation in young girl.
  • Early menopause: The fewer years a woman menstruates, the shorter the time her breast tissue is exposed to estrogen.

Selective estrogen receptor modulators (SERMs) are drugs that act like estrogen on some tissues in the body, but block the effect of estrogen on other tissues. Tamoxifen is a SERM which is called antiestrogens. Antiestrogens block the effects of the hormone estrogen in the body. Tamoxifen lowers the risk of breast cancer in women who are at high risk for the disease. This effect lasts for several years after drug treatment is stopped. Taking tamoxifen increases the risk of developing other serious conditions, including endometrial cancer, stroke, cataracts, and blood clots, especially in the lungs and legs.