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Breast Cancer Risk Declines with Each Childbirth Before Age 30 (dateline January 24, 2001)

Physicians know that women who begin having children before age 30 have a lower risk of breast cancer compared to women who have children later in life or never have children. Now Danish researchers have found that the more children a woman has before age 30, the lower her risk of breast cancer. The results of the study suggest that the current view about childbirth and breast cancer risk should be modified to explain that multiple births at an earlier age decrease a woman’s risk of breast cancer.

In the study, researchers analyzed medical records from 1.5 million Danish women born between 1935 and 1978, 13,049 of whom had breast cancer. According to Jan Wohlfahrt and Mads Melbye of the Staten Serum Institut in Copenhagen, a woman’s breast cancer risk is related to her age at any of her births. Among women who have a first child before age 25, each additional birth reduces their risk of breast cancer.

According to the researchers, for every five-year increase in age when she has her first, second, third, or fourth child, a woman’s risk of breast cancer increases. Thus Wohlfahrt and Melbye conclude that a woman’s early reproductive years could be key and that having children during these years may reduce the long-term risk of breast cancer.

Experts believe that estrogen exposure plays a role in breast cancer risk. The more menstrual cycles a woman has throughout her lifetime, the higher her risk of breast cancer. For example, women who begin menstruating at an early age (before age 12) and those who reach menopause after age 50 have an increased risk of breast cancer. During pregnancy, women do not typically experience menstrual cycles, which is thought to reduce the risk of breast cancer.

A woman’s age when she has children and when she begins and finishes menstruation are only a few risk factors for breast cancer. Other risk factors for breast cancer include:

However, it is estimated that approximately 80% of women who develop breast cancer have no identifiable risk factors. Therefore, to help detect breast cancer early, when it is most likely to be successfully treated, women should practice monthly breast self-exams, receive regular physician-performed clinical breast exams, and receive annual screening mammograms (beginning at age 40).

Guidelines for early breast cancer detection:

  • All women between 20 and 39 years of age should practice monthly breast self-exams and have a physician performed clinical breast exam at least every three years.
  • All women 40 years of age and older should have annual screening mammograms, practice monthly breast self-exams, and have yearly clinical breast exams.
  • Women with a family history of breast cancer or those who test positive for the BRCA1 (breast cancer gene 1) or BRCA2 (breast cancer gene 2) mutations may want to talk to their physicians about beginning annual screening mammograms earlier than age 40, as early as age 25 in some cases.

Additional Resources and References