Though several small studies have suggested that Study: Breast-Feeding and Having Many Children Reduce Breast Cancer Risk (dateline October 24, 2002) | Breast Health News | Imaginis - The Women's Health & Wellness Resource Network

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Study: Breast-Feeding and Having Many Children Reduce Breast Cancer Risk (dateline October 24, 2002)

Though several small studies have suggested that breast-feeding reduces a woman’s risk of developing breast cancer, experts have needed assurance from larger, more diverse analyses. Now, a compilation of 47 studies involving 150,000 women from 30 countries has been published that further supports this claim. The analysis—the most extensive study on breast-feeding and breast cancer ever conducted—found that having more children and breast-feeding for a longer period of time protect against breast cancer. The report may provide researchers with important information in understanding why breast cancer develops.

Professor Valerie Beral and her colleagues from the charitable organization, Cancer Research UK, analyzed records of 50,000 women with breast cancer and 100,000 healthy women to determine whether breast-feeding impacts breast cancer risk. A key component of the research was to compare women from developed countries with those from undeveloped countries where childbirth habits tend to differ. The research was published in the July 20, 2002 issue of The Lancet.

The findings showed that the amount of time a woman breast-feeds significant affects her risk of developing breast cancer. For each year of breast-feeding, breast cancer risk is reduced by 4.3%. In addition, women lower their breast cancer risk by 7% for each child they bear.

"The results of this study are a major step forward in our understanding of why breast cancer incidence is so high in developed countries," said Professor Beral in a Cancer Research UK news release. "It's long been known that breast cancer is common in situations where women have few children and breastfeed for short periods. We've shown that these factors alone account for much of the high rates of breast cancer in these settings."

In the analysis, researchers found that women from Western countries tended to have two to three children and breast-fed those children for an average of two or three months each. By contrast, women from undeveloped countries had approximately six to seven children and breast-feed each of those children for an average of two years.

"To expect that substantial reductions in breast cancer incidence could be brought about by women returning to the pattern of childbearing and breastfeeding that typified most societies until a century or so ago is unrealistic," said researcher Gillian Reeves of Cancer Research UK, in a news release about the study. "But even if women in the West were to breastfeed each of their children for an extra six months this could prevent five per cent of breast cancers each year."

The American Academy of Pediatricians and the National Association of Pediatric Nurses Associates and Practitioners recommend breast-feeding as much as possible during the baby’s first year. In addition to reducing breast cancer risk, breast-feeding has been shown to have several other beneficial effects including protection against infant ear infections, allergies, diarrhea, eczema, bacterial meningitis, and other serious illnesses and reducing infant anemia (iron deficiency in the blood) and stomach or intestinal infections.

Breast-feeding also offers benefits to nursing mothers. Breast-feeding releases hormones which cause the uterus to shrink after delivery and also decreases bleeding. Mothers who breast-feed typically have an easier time losing weight after pregnancy. According to the American Academy of Pediatrics, breast-feeding also helps build a woman’s bone mineral density and helps prevent osteoporosis after menopause.

Though the researchers did not investigate how breast-feeding reduces breast cancer risk, experts believe that breast-feeding may suppress the hormone estrogen, which is needed to fuel many types of breast cancer.

Additional Resources and References

  • The paper, "Breast Cancer and Breastfeeding: Collaborative Reanalysis of Individual Data from 47 Epidemiological Studies in 30 Countries, Including 50,302 Women with Breast Cancer and 96,973 Women Without the Disease," is published in the July 20, 2002 issue of The Lancet:
  • The July 19, 2002 Cancer Research UK report, "Breastfeeding Provides Major Protection Against Breast Cancer," is available at
  • To learn more about breast-feeding, please visit