Updated July 02, 2015.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Don’t Feel Guilty

Not all women can or should breastfeed, and that’s a medical fact. If you are in this category, you should not feel guilty for formula-feeding your infant. Infant formulas are the next best thing, and they offer a healthy alternative.

Breast Milk -- It's Still the Best Milk

This message should not be diluted in reaching Moms who are interested in breastfeeding, and the reasons follow.

According to the American Academy of Pediatrics, some Moms start out enthusiastically wanting to breastfeed but find the obstacles too formidable. Others start out trying to breastfeed but lack the encouragement and support to continue for very long. Well-meaning friends and family -- and the occasional husband who’s had enough with all the pumping and freezer storage bags -- all may contribute to subtly sabotage Mom’s breastfeeding efforts. Not to mention ad campaigns by the baby formula industry.

Benefits of Breastfeeding

The benefits of breastfeeding are too numerous and complex to cover in an article about leukemia. Aside from being the perfect infant food as relates to nutrition and digestibility, there is the added immune protection for baby. Antibodies and other germ-fighting substances pass from Mom to baby and strengthen the immune system, helping to lower the risk for many early childhood illnesses, including ear infections, diarrhea, respiratory infections and meningitis. For more on the health benefits see “The Benefits of Breastfeeding by Donna Murray.”

Leukemia Breastfeeding Studies

Breastfeeding has immune effects in babies resulting in a protective effect against certain infections and illnesses. At first, small studies suggested there might be a protective effect against childhood Hodgkin disease and lymphoma, as well.

Children’s Cancer Group Study

Then, the Children’s Cancer Group undertook a large study to identify risk factors for childhood leukemia – specifically, acute myeloid leukemia, or AML, and acute lymphoblastic leukemia, or ALL. They found that breast-fed infants had a reduced risk of childhood acute leukemia, both AML and ALL. Breastfeeding appeared to lower the risk of childhood AML and ALL, particularly in those infants who were breast-fed for more than 6 months. Leukemia risk tended to decrease as the length of time spent breast-feeding increased -- up to 12 months for ALL and 9 months for AML.

Childhood Leukemia International Consortium Study

More recently, investigators examined data from a research program called the Childhood Leukemia International Consortium, with cases spanning the years 1980-2010. This study included 7,399 children who developed ALL and 11,181 children aged 2-14 who did not develop ALL. Breastfeeding was associated with a lower risk of ALL. Interestingly, so was day-care center attendance during the first year of life.

JAMA Study - Childhood Leukemia Risk Cut by 19 Percent

Then came the study in June of 2015 in the Journal of the American Medical Association, or JAMA, suggesting breastfeeding may help lower childhood leukemia incidence, in addition to the established benefits for children and Moms.

Breastfeeding for 6 months or longer compared with a shorter duration or not breastfeeding at all was associated with a 19 percent lower risk for childhood leukemia. An association was still seen when Moms did some breastfeeding but not for the full 6 months. In this case there was an 11 percent lower risk.

How Might Breastfeeding Lower Risk?

Researchers point to the biology of breast milk -- including the effect of human milk on germs, infections and the developing immune system in infants. Infant formula changes the infants’ gut bacteria, thus affecting the response of the infant's immune system to viruses and bacteria. A recent additional discovery is that breast milk contains stem cells that are in some ways similar to human embryonic stem cells. The breastfed infant ingests thousands to millions daily, and one theory is that these might be specifically involved in immunity and other factors that influence leukemia. Growth factors and chemical signals have also been identified in human milk. It has been shown that they may play a role in the development of leukemia.

Breastfeeding and Leukemia Background

For more on breastfeeding and childhood leukemia, explore the following sources:

Shu XO, Linet MS, Steinbuch M et al. Breast-feeding and risk of childhood acute leukemia. J Natl Cancer Inst. 1999. 20;91(20):1765-72.

J Rudant, T Lightfoot, KY Urayama et al. Childhood Acute Lymphoblastic Leukemia and Indicators of Early Immune Stimulation: A Childhood Leukemia International Consortium Study. Am J Epidemiol. 2015.

Amitay EL, Keinan-Boker L. Breastfeeding and Childhood Leukemia Incidence: A Meta-analysis and Systematic Review. JAMA Pediatr. 2015;169(6):e151025.