African-American women who do not breastfeed their babies face a higher risk of getting an aggressive form of breast cancer than their counterparts who nurse, said a US study on Tuesday.
The analysis found that women who had two or more children faced a 50 percent increased risk of hormone receptor-negative breast cancer, one of the toughest kinds to treat.
But this higher risk was only present in women who did not breastfeed their children.
"African-American women are more likely to have had a greater number of full-term births and less likely to have breast-fed their babies," said Julie Palmer, professor of epidemiology at the Slone Epidemiology Center at Boston University.
"This study shows a clear link between that and hormone receptor-negative breast cancer."
Data for the research, published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research, came from the Black Women's Health Study which has followed 59,000 women since 1995.
From 1995 to 2009, researchers found 457 cases of hormone receptor-positive breast cancer and 318 cases of hormone receptor-negative breast cancer among study participants.
Among those diagnosed with hormone receptor positive breast cancer, which also tends to occur more frequently in white women, there was no link to the number of children a woman had and whether or not she breastfed.
"Our results, taken together with recent results from studies of triple negative and basal-like breast cancer, suggest that breastfeeding can reduce risk of developing the aggressive, difficult-to-treat breast cancers that disproportionately affect African-American women," Palmer said.
According to the Centers for Disease Control and Prevention, about 35 percent of white women in the United States are breastfeeding their babies at six months of age compared to 20 percent of black women.
Breast cancer is expected to kill nearly 40,000 people (39,520 women, 450 men) this year in the United States, according to the National Cancer Institute. It is the second leading killer among women after lung cancer.