The ability of breast milk to protect infants against respiratory viruses is gender-biased in favor of girls, reveal studies by Dr. Fernando Polack. Polack’s first study appeared last June in Pediatrics, and the second came out in February’s Pediatric Infectious Disease Journal. The research took place at hospitals in Buenos Aires, Argentina, through Polack’s INFANT foundation research facility.
“We were really looking for evidence that breast milk might protect against human meta-pneumovirus, for which there is no vaccine. But when we saw how significant this difference between boys and girls was, we were a bit surprised,” Polack says.
Recently named the Cesar Milstein Associate Professor of Pediatric Infectious Diseases at the Monroe Carell Jr. Children’s Hospital at Vanderbilt, Polack is studying alternatives to protect newborn babies against respiratory viruses, especially very vulnerable premature infants.
Polack knew of anecdotal evidence suggesting a gender difference in the protective effect of breast feeding, but the few small studies reinforcing the idea have not garnered much attention.
His study in Pediatrics examined the effect in very low birth-weight babies. He found that once baby girls left the neonatal intensive care unit, those who were getting breast milk since birth were rarely rehospitalized for respiratory infections. The big surprise was that girls who were not breast-fed were at the highest risk for rehospitalization, outstripping the risk for boys. The difference between breast-fed boys and non–breast-fed boys was not statistically significant.
The most recent study, involving full-term babies, showed roughly the same thing. But beyond revealing a thought-provoking difference between boys and girls, Polack says his work brings up the more important question, How does the protection of breast milk work?
“We used to think breast milk was an immune-system boost, pre-made from the mother and ready to be used by the baby. But if that were the case, gender should not make a difference. This suggests the protection is in the baby at birth,” Polack says.
Polack believes some immune process is present within babies at birth with the potential to offer “nonspecific” antiviral protection.
“At least for girls, breast milk may trigger this protection that is nonspecific, protecting against all the viruses we looked at—and we looked at a dozen or more viruses.”
This points to the potential of discovering a natural human substance, or new immune mechanism, that can provide people with antiviral protection without having to be exposed to a virus first (the mechanism employed in vaccine development).
“We have been testing vaccines more than 40 years with the idea that we need a single vaccine for each organism. But today we have no single vaccine for infants under 6 months of age,” says Polack. “Vaccines are very important. But this is evidence that we may have an alternate method we never imagined.”
No one should read into this work that breast milk is not beneficial to baby boys, Polack emphasizes. Numerous other benefits of breast milk exist beyond protection from respiratory illness. And Polack believes boys do receive some respiratory protection too, but more research is needed to show it.