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Longer Breastfeeding Could Cut Breast Cancer In Developed World

Lancet

07/18/2002
By Harvey McConnell
 

Breast cancer among women in developed countries could be reduced dramatically if they breastfed longer.

This has been found in analysis of 47 studies, involving 147,275 women from 30 countries.

"The results of this study are a major step forward in our understanding of why breast cancer is so common in developed countries," declares Dr Valerie Beral, Cancer Research UK, Radcliffe Infirmary, Oxford, England, and lead author of the study by the international Collaborative Group on Hormonal Factors in Breast Cancer.

"It has long been known that breast cancer was common in situations where women had few children breastfed for short periods. We have shown that these factors alone account for the high rates of breast cancer in more-developed settings."

An estimated 25,000 breast cancers could be prevented in Western populations every year if women continued to have the same number of children, but breastfed each child for six months longer, the clinicians have found.

Although childbearing is known to protect against breast cancer, what contribution breastfeeding has on this protective effect, if any, has been difficult to determine, the clinicians point out.

The researchers pooled and analysed data that included breastfeeding patterns and other aspects of childbearing for 50 302 women with invasive breast cancer and another 96 973 women who were controls.

Women with breast cancer had fewer children on average (2.2) than women who did not develop breast cancer (2.6).Twenty-nine percent of women who developed breast cancer, compared with 21 percent of those who did not develop breast cancer, had never breastfed.

Among women who did breastfeed, those who developed breast cancer had a shorter lifetime duration of breastfeeding, around 10 months, compared with women who did not develop breast cancer, around 16 months.

Overall, the clinicians found that the relative risk of breast cancer decreased by 4.3 percent for every year of breastfeeding, in addition to a decrease of 7 percent for each birth. This pattern of risk was seen consistently for women from developed and developing countries, and for women of different ages and numbers of children.

The researchers estimate that the cumulative incidence of breast cancer in developed countries would be reduced by more than half, from 6.3 to 2.7 per 100 women by age 70, if women had the average number of births, and lifetime duration of breastfeeding, that had been prevalent in developing countries until recently.

They acknowledge that "to expect that substantial reductions in breast-cancer incidence could be brought about today by women returning to the pattern of childbearing and breastfeeding that typified most societies until a century or so ago is unrealistic.

"However, if in the future the mechanism of the protective effect of breastfeeding on breast cancer were understood, it might be possible to prevent breast cancer by mimicking the effect of breastfeeding therapeutically or in some other way."

Lancet 2002; 360: 187-95.

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