Breast milk has been found to help protect babies against a potentially fatal bowel condition called necrotising enterocolitis.
The devastating disorder, known as NEC, kills 39% of babies who get the disease and survivors face lifelong consequences, including the removal of part of their intestine and dependence on intravenous nutrition.
NEC is the result of the loss of specialised intestinal, "Paneth", cells. These cells protect the organ from microbial damage and sustain stem cells needed for ongoing renewal of the intestines lining.
Scientists at the Children's Hospital Los Angeles have found a protein called neuregulin-4 (NRG4), which is found in breast milk but not baby formula, may be protective against the destruction caused by NEC.
Published in the American Journal of Pathology, investigators showed how NRG4 prevented the loss of Paneth cells.
Mark R Frey, principal investigator, said: "Our research suggests that without the NRG4 protein found in breast milk, a normal protection mechanism for the immature gut may be missing. If a baby on formula encounters an NEC trigger such as intestinal infection or injury, he or she may be at an increased risk for a life-threatening condition."
Scientists tested their theory on rats, used in vitro studies, and examined human breast milk and infant intestinal tissue. Formula-fed rats developed an NEC-like condition while those that received formula with NRG4 did not.
Researchers believe NRG4 binds with a receptor in the intestine to block inflammatory intestinal damage.
Frey said: "We're finding a protective protein in breast milk, with its receptor in the intestine. Given that NEC is a significant clinical problem without an effective treatment, we plan to evaluate NRG4 for its therapeutic potential in this disease."
Around 3,000 babies develop NEC each year in the UK.