Study: Breast-feeding lowers cancer risk
CNN Medical Unit
(CNN) -- Women who breast-feed longer and bear more children are better protected from breast cancer, according to new study published in the British medical journal The Lancet.
Researchers found if women in developed countries breast-fed their children just six months longer than they do now, 25,000 breast cancers worldwide could be prevented each year.
"Yesterday you would have been told we don't know what the major causes for breast cancer are," said Valerie Beral, lead author of the study and an epidemiologist with Cancer Research UK.
"Now what we're saying is that we do know what the major causes for breast cancers are, and we don't know what to do about them yet. It's complicated."
Researchers compared data from 47 studies in 30 countries and found the incidence of breast cancer lower among women in developing countries because they tend to have more children and breast-feed longer than women in developed countries.
The study involved 50,302 women with breast cancer and 96,973 without the disease.
According to the study, a woman's risk for breast cancer decreased by about 4.3 percent for every 12 months she breast-fed. The risk went down 7 percent more for every child born.
Beral said women in developing countries of Asia and Africa still have many more children and breast-feed much longer than women in the United States or in Europe.
"This is the main reason why breast cancer is common in the U.S. and it's uncommon in developing countries," Beral said. "The number of children women have and how long they breast-feed is different."
Data provided in the study showed that if women in developed countries such as the United States and Britain have an average of 2.5 children and breast-feed for approximately three months, their risk for getting breast cancer by age 70 is 6.3 percent.
That is because they are breast-feeding for approximately eight months in their lifetime.
By contrast, women in developing countries -- in Asia or Africa, for example -- who bear six or seven children and breast-feed them for two years each will be breast-feeding for about 13 years.
According to the study, their risk for breast cancer by age 70 is only 2.7 percent -- a more than a 50 percent decrease compared to their counterparts in the developed world.
Eugenia Calle, director of analytic epidemiology for the American Cancer Society in Atlanta, Georgia, said scientists, women and the media all want to identify the culprit for the cause of breast cancer.
"The dramatic changes that have occurred in childbearing over past 50 to 75 years really can explain a fairly large amount of breast cancer incidence in developed countries," Calle said.
"This might encourage women to breast-feed a little longer. You're not going to hugely increase the benefit, but every little bit helps," she said.
The American Academy of Pediatrics recommends "exclusive breast-feeding for approximately the first six months after birth and that breast-feeding continue for at least 12 months and thereafter for as long as is mutually desired."
World Health Organization recommendations go even further, suggesting women continue "to breast-feed up to two years or longer."
Beral said the study did not offer any recommendations, noting that the "practical implications are very complex."
Beral and Calle agreed it was unrealistic to think Western women would revert to a lifestyle from two centuries ago.
"The take-home message is that this study gives us a more definitive reason that breast-feeding is one way to reduce risk of breast cancer," said Dr. Anne McTiernan with the Fred Hutchinson Cancer Research Center in Seattle, Washington.
McTiernan, author of the book "Breast Fitness," also stressed there are other ways for women to reduce their risk for breast cancer, including exercising three or more hours a week, which she said reduces one's risk for breast cancer by 30 to 40 percent.
The study was funded by Cancer Research UK and the WHO.
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