Breastfeeding for even a few months may lower the odds that a child will develop leukemia, a new research review suggests.

The analysis of 14 studies conducted since 1988 found that overall, longer-term breastfeeding was linked to a 24 percent lower risk of acute lymphoblastic leukemia (ALL), the most common form of childhood leukemia. Breastfeeding for 6 months or less appeared to reduce ALL risk by 12 percent.

Breastfeeding was also linked to a lower risk of acute myeloblastic leukemia (AML), a form of the cancer that in recent decades has accounted for 16 percent of leukemia cases among U.S. children.

Leukemia is a disease in which the bone marrow produces large numbers of abnormal, immature white blood cells, crowding out normal blood cells over time. The core difference between ALL and AML is in the type of white blood cell affected.

In the past, individual studies have yielded conflicting results on whether breastfeeding affects children’s leukemia risk. But the new findings, based on international studies including more than 8,000 children with ALL or AML, offer a “strong suggestion” that breastfeeding is protective, Dr. Marilyn Kwan of the University of California, Berkeley, told Reuters Health.

She and her colleagues report the findings in the current issue of the journal Public Health Reports.

Breastfeeding is known to have a number of health benefits, including a lower risk of common childhood infections. It’s this particular benefit, according to Kwan, that may explain the connection between breastfeeding and lower leukemia risk.

Other researchers have theorized that a rare, abnormal immune response to early-life infection may play a role in ALL. In children with genetic aberrations that predispose them to the disease, such an abnormal immune response could act as a “secondary promoting event” that results in ALL, Kwan explained.

Breastfeeding, through its benefits for the developing immune system, may protect against such an immune response.

The finding that breastfeeding was also related to a lower risk of AML was “not anticipated on biological grounds,” the researchers note in the report.

It’s possible, Kwan said, that a separate immune-based mechanism underlies this relationship, but more research is needed to answer that question.

Although leukemia is the most common childhood cancer in the U.S., it is relatively rare for children to develop cancer. And Kwan cautioned that women who cannot breastfeed should not worry they are putting their children at greater cancer risk.

Instead, she said, this study suggests that lower leukemia risk might be something to “add to the list” of the potential benefits of breastfeeding.

SOURCE: Public Health Reports, November/December 2004.