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Breast-Feeding May Significantly Reduce Breast Cancer Risk for Mothers (dateline February 2, 2001)


A study of over 800 women in China found that breast-feeding for two years may reduce a woman’s risk of developing breast cancer by as much as 50% compared to women who breast-feed for less than six months. The study is significant because it shows that breast-feeding can lower breast cancer risk both before and after menopause whereas most previous breast-feeding studies only revealed a reduced cancer risk for pre-menopausal women. The study did not investigate why breast-feeding cut the risk of breast cancer, but researchers believe it may be related to reduced exposure to estrogen and female hormone cycles during lactation.

To conduct the study, Dr. Tongzhang Zheng, Associate Professor of Epidemiology and Public Health at Yale University School of Medicine, and his colleagues enrolled 404 women between the ages of 30 and 80 who had breast-fed their children and an equal number of women who had not breast-fed. The researchers interviewed the women to gather information about lactation, menstruation, and reproduction.

Their findings show that women who breast-fed for more than 24 months per child had a reduced risk of breast cancer compared with women who breast-fed only one to six months per child. The risk of breast cancer was also significantly lower for women who breast-fed more than 73 months over their lifetime. Of importance, the risk of breast cancer was reduced both before menopause and after menopause.

Although more than 60% of American women breast-feed their children, statistics show that only one-third continue breast-feeding longer than six months. Experts attribute this lack of breast-feeding to the negative perception of breast-feeding that exists in America. By contrast, in China, breast-feeding children for the first two years is socially accepted.

In the study, researchers also added to a large amount of research which shows that the early onset of menstruation (before age 12), late menopause (after age 50) and having a first child after age 30 all contribute to an increased risk of developing 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.

Though the study did not specifically address the reason why breast-feeding may reduce breast cancer risk, Dr. Zheng suggests that the suppression of estrogen and female hormone cycles may be one explanation for the protective effect. However, further research is needed to understand how breast-feeding lowers this cancer risk. In the study, the number of children breast-fed and the age at the time of lactation did not appear to influence breast cancer risk.

Many risk factors for breast cancer, including advancing age, family history, age of first menstruation, etc. are uncontrollable. Breast-feeding is one factor that can be controlled, said Dr. Zheng. Breast-feeding has also been shown to be associated with a number of benefits to children, including a reduction of infant ear infections, allergies, diarrhea, bacterial meningitis, and other serious illnesses.

Breast-feeding is a personal decision a mother needs to make carefully, taking full into account the benefits and burdens it will bring to both her and her baby. The American Academy of Pediatrics and other organizations actively promote the benefits of breast-feeding. The American Academy of Pediatrics hopes to increase the number of American women who breast-feed their children to at least 75% in the early postpartum period, at least 50% up until their babies are 6 months old, and at least 25% up until 12 months.

If a mother does decide to breast-feed her children, she should understand that breast-feeding is a major responsibility that requires her to maintain excellent nutrition and health. Most physicians agree that caffeine intake should be kept to a minimum during breast-feeding and that alcohol should not be consumed during this time.

To help detect breast cancer at early stages, when the chances for successful treatment and survival are the greatest, women should follow these guidelines set by the American Cancer Society:

  • 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. The clinical breast exam should be conducted close to and preferably before the scheduled mammogram.
  • 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.

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