LLLI Center for Breastfeeding Information

Journal Abstract of the Month for August 2002

"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" Lancet 2002-7-20;360:187-95.

The Collaborative Group on Hormonal Factors in Breast Cancer, headed by Professor Valerie Beral from the Cancer Research UK at Oxford reviewed 47 epidemiological studies on the effect which parity and breastfeeding has on the incidence of breast cancer in 30 countries around the world. They found that women with breast cancer had on average, fewer births than did controls. Fewer mothers with cancer had breastfed as compared to mothers who did breastfeed. The relative risk of breast cancer decreased by 4.3% for every 12 months of breastfeeding in addition to a decrease of 7.0% for each birth. Whether the mothers lived in developing countries or developed countries did not affect the outcome.

The authors estimate that the total 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.
Most studies examined did not differentiate between breastfeeding with supplements and exclusive breastfeeding. Comparatively few women reported lifetime durations of breastfeeding for longer than 30 months: 7% of those with breast cancer and 15% of the control group without cancer.

The authors suggest that the major reasons for the high incidence of breast cancer in developed countries are the small family size and the short duration of breastfeeding. Important reductions in breast-cancer incidence could be achieved if women considered breastfeeding each child for longer than they do now.

Based on the estimates obtained in this paper, if women in developed countries had 2.5 children, on average, but breastfed each child for 6 months longer than they currently do, about 25,000 (5%) cancers would be prevented each year, and if each child were breastfed for an additional 12 months about 50,000 (11%) breast cancers might be prevented annually.

This article was categorized using the keywords: Breast Cancer, Extended Breastfeeding, Parity, Trends.