Study: Breastfed children have slightly lower risk of childhood leukemia

Liz Szabo | USA TODAY

Breastfeeding has well-known health benefits for both moms and babies. Now a new analysis finds that breastfed babies also have a 14% to 19% lower risk of pediatric leukemia, the most common childhood cancer.

The analysis, which examined 18 previously published studies, was published Monday in JAMA Pediatrics.

The study doesn't prove that breastfeeding prevents cancer, said Elizabeth Ward, an epidemiologist with the American Cancer Society, who wasn't involved in the new research. That's because the studies were conducted by interviewing the mothers of children with leukemia and comparing their answers to those of mothers of kids without cancer.

This type of study has inherent limitations because women whose children develop leukemia may remember things differently than those whose kids remain healthy, Ward said. At most, the analysis suggests an association between breastfeeding and reduced risk. But factors other than breastfeeding might also explain that link.

And the study, said Ward, led by Efrat Amitay of the University of Haifa in Israel, shouldn't cause mothers of children with cancer to worry that they did anything wrong if they didn't breastfeed for six months (the length of time used in the study). "We can't tell what causes any one individual's cancer," Ward said. "There are thousands of kids in the United States who aren't breastfed, and the vast majority don't get leukemia."

Breastfeeding is unlikely to tip the balance in determining whether a child develops cancer or not, pediatric oncologist Patrick Brown, a spokesman for the American Society of Hematology, said.

"Breastfeeding is part of a complicated health environment that may very well affect the incidence of childhood leukemia" in a large population, said Brown, who directs the pediatric leukemia program at the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins. "By no means should that be interpreted to say that an individual child's case is caused by the fact that the mother did or did not breastfeed. By no means should that be used as a cause for feelings of guilt or blame."

A child's overall risk of childhood leukemia is extremely low, affecting one in 20,000 children, Brown said. If the study's conclusions are correct, breastfeeding would decrease a child's risk of leukemia from 0.005% to 0.004%, Brown said.

Researchers aren't likely to resolve the question any time soon, Ward said. The best way to get a solid answer on the relationship between breastfeeding and childhood cancer would be to follow children from infancy to see which ones develop cancer. With pediatric leukemia so rare, such a study could require hundreds of thousands of children, Ward said.

Doctors diagnosed about 15,780 children and adolescents under age 20 with cancer in 2014, according to the American Cancer Society. That includes about 4,100 cases of leukemia.

Women have many other reasons to try to breastfeed, said Rosemary Higgins, a neonatologist at the Eunice Kennedy Shriver National Institute of Child Health and Human Development, part of the National Institutes of Health. First, breastfeeding can help moms and babies to bond.

In addition, mothers who breastfeed tend to lose their pregnancy weight faster and have a lower risk of breast and ovarian cancer, Higgins said.

Mothers who breastfeed also pass on their antibodies, which can strengthen a baby's immune system and help fight infection. Breastfed babies are less likely to be hospitalized and to die of Sudden Infant Death Syndrome. They have lower rates of allergies, ear infections, diarrhea and diabetes. They also score higher on intelligence tests in later childhood, Higgins said.

Because of these benefits, the American Academy of Pediatrics recommends mothers breastfeed exclusively for a baby's first six months, then combine breast milk and other foods until a baby is 12 months old, or for as long as a mom and baby enjoy it.

Breastfeeding rates vary by income and education, with better-educated women more likely to nurse than others.

"Breast milk is the perfect food for babies," Higgins said. "Nature made it that way."