Keck School of Medicine researchers report that African-American women are having fewer children and breastfeeding less, which might translate to escalating rates of breast cancer in the African-American community.
The risk of developing breast cancer in African-American women – as in white women – declines the more children they have and the greater time they spend breast-feeding, authors report in an article in a recent issue of the journal Cancer.
Overall, African-American women today have a lower risk of breast cancer than white women, but breast cancer cases among African-American women are likely to accelerate if current birth and breastfeeding patterns continue, the researchers suggested.
"Our finding that certain reproductive factors can reduce breast cancer risk for African-American women, as they do for white women, confirms that breast cancer development in African Americans is similar to that in whites,” said Giske Ursin, associate professor of preventive medicine at the Keck School and lead author of the study.
“We hope our research will give African-American women extra motivation to breastfeed their children.”
Although researchers have long known that the number of pregnancies and the duration of breastfeeding both lower risk of breast cancer among white women, few studies have investigated whether these factors can protect women of other races and ethnicities. Ursin and her colleagues conducted the Women’s Contraceptive and Reproductive Experiences, or CARE, study to find some answers.
The researchers looked at 4,567 women ages 35 to 64 who were diagnosed with breast cancer between 1994 and 1998 in five metropolitan areas. Of these women, 2,950 were white and 1,617 were African-American. They compared them to another group of 4,668 women (3,012 white and 1,656 African-American) from the same areas.
Ursin and her colleagues found that breast cancer risk decreased with each pregnancy, especially among younger women (ages 35 to 49). Among whites, each pregnancy dropped breast cancer risk by 13 percent among younger women and by 10 percent among older women. Among African Americans, each pregnancy dropped breast cancer risk by 10 percent among younger women and by 6 percent among older women.
Breastfeeding also proved protective for both groups of women. Women who had breastfed for at least two weeks had about 30 percent lower risk of breast cancer than women who had not breastfed at all, Ursin said. Breastfeeding appeared to protect women particularly strongly in the five years after breastfeeding occurred, but protection continued afterward, as well.
Researchers found that African Americans had more children, on average, than whites. But when they looked at young women specifically, researchers saw differences narrow in childbearing rates between African-American women and white women. Young African-American women were having fewer children than before. At the same time, young white women breastfed almost twice as long as African-American women.
“If breastfeeding rates remain low, and the number of children young African-American women have is dropping over time, then this could result in a more rapid increase in breast cancer rates in this group than in whites,” Ursin said. She and her colleagues suggest that encouraging African-American women to breastfeed, and to breastfeed for a longer time, might help reduce the risk of breast cancer.
Although exact causes are unclear, scientists believe reproductive factors such as breastfeeding and childbearing reduce risk for breast cancer by affecting women’s hormone levels, breast tissue differentiation or other mechanisms.
The Women’s CARE study is supported by the National Institute of Child Health and Development, one of the National Institutes of Health. The National Cancer Institute provided additional support.