Leukemia is a cancer of the bone morrow that impedes the natural formation of blood cells. Despite being the most common childhood cancer - accounting for about 30% of all cancers in childhood - little is known about the cause of leukemia.

Worldwide, about 175,000 leukemia cases are diagnosed in children under the age of 15 each year. Advancements in treatment technologies have improved survival rates - and the cancer is still relatively rare - yet leukemia is still the second highest cause of death among under-15s in the US, where it is surpassed only by accidents.

Known risk factors for leukemia include Down syndrome and exposure to Epstein-Barr virus or ionizing radiation. The majority of children diagnosed with leukemia do not present with these risk factors, however.

For the new systematic review and meta-analysis, researchers from the University of Haifa, Israel, reviewed evidence from 18 studies examining the impacts of breastfeeding on risk of childhood leukemia.

The authors report that, based on the evidence in these studies, breastfeeding for 6 months or longer was linked to a 19% decreased risk of leukemia compared with no breastfeeding or breastfeeding for a shorter period.

Children who were breastfed for any duration had an 11% lower risk for childhood leukemia, compared with children who were never breastfed.

How does breast milk protect again leukemia?

Suggesting a potential mechanism behind the protective effects of breast milk, the authors explain that breast milk influences the development of an infant's immune system as it contains assorted immunologically active components and anti-inflammatory defense mechanisms. These mechanisms may include conferring a "more favorable" gut microbiome to the infant as well as supplying stem cells.

Breast milk is a "total food," the researchers explain, able to exclusively supply all of infants' nutritional needs. Both the American Academy of Pediatrics and the World Health Organization currently recommend that babies should be exclusively breastfed for the first 6 months of life to ensure healthy growth and development.

After that first 6 months, it is recommended that infants receive nutritious and safe complementary foods, but that breastfeeding can continue for up to 2 years, or even longer.

The authors write:

"Because the primary goal of public health is prevention of morbidity, health care professionals should be taught the potential health benefits of breastfeeding and given tools to assist mothers with breastfeeding, whether themselves or with referrals to others who can help. The many potential preventive health benefits of breastfeeding should also be communicated openly to the general public, not only to mothers, so breastfeeding can be more socially accepted and facilitated. In addition, more high-quality studies are needed to clarify the biological mechanisms underlying this association between breastfeeding and lower childhood leukemia morbidity."

One potential limitation of this analysis was that the researchers only looked at case-control observational studies, which could have included selection bias, as well as various confounding factors that could influence both breastfeeding behaviors and childhood leukemia risk.

Recently, Medical News Today looked at a study that found breastfeeding is linked with a 30% overall decreased risk of breast cancer recurrence among mothers who have previously had one subtype of the disease.

Written by David McNamee