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Last updated on April 21, 2014 at 7:52 EDT

Breast Feeding Lowers Risk of Breast Cancer

May 10, 2008

New research has found that women who were breast-fed as infants may be at lower risk of breast cancer than those who were not breast fed. However, there appears to be no difference in breast cancer risk in first-born children, regardless of whether or not they were breast-fed. 

“As a general group, women who reported they had been breast-fed in infancy had a 17 percent decrease in breast cancer risk,” Hazel B. Nichols of the University of Wisconsin, who was involved in the study, said during a Reuters interview.

“However, we did not observe this reduction when we looked specifically among first-born women,” she said.

In a report about the study, Nichols and her team wrote that a woman’s age at childbirth can help predict the amount of environmental contaminants in her breast milk. Previous studies suggest the accumulation of these contaminants are linked to an increased risk of breast cancer. 

The researchers interviewed 2,016 women 20 to 69 years old who had been diagnosed with breast cancer, and 1,960 similar women who did not have breast cancer. They wanted to determine whether a woman’s birth order, breast feeding status and mother’s age at the time of her birth were associated with a change in her breast cancer risk. 

In general, they discovered that women who were breast-fed during infancy had a reduced breast cancer risk.  However, in a review of breast-fed women only, those with 3 or more older siblings had a lesser risk for breast cancer than first-born women.

The study also showed that a mother’s age at the time of childbirth did not alter the breast cancer risk. But among women who were not breast-fed, reduced adult breast cancer risk was linked with their mothers’ older age at childbirth. However, the researchers found no link between birth order and breast cancer risk in this group.

Nichols said additional research is needed to determine if the associations found in the study vary according to measured levels of environmental contaminants present in breast milk or with duration of breast-feeding. But she said the current study does point to differences in breast cancer risks based on whether or not a women was breast-fed as an infant.

Nichols and colleagues published a report about the study in the medical journal Epidemiology. A summary of the report can be viewed here.