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why breastmilk reduces allergies

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Why does breastmilk reduce the chance of allergies?

New study narrows it down to a few tiny molecules

It isn’t news that breastfed babies tend to develop fewer allergies than those fed with formula. Researchers, lactation consultants and other experts have been telling new parents about this particular benefit of nursing since 1936. That’s when scientists first made the connection that infants who were nursed rather than formula-fed were significantly less likely to develop eczema – a skin allergy.

What is news? A new study recently published in The American Journal of Clinical Nutrition, which offers insights into why breastfeeding reduces allergy development. 

The why

The new science, conducted by Penn State College researchers, finds that tiny molecules found in human milk are a significant source of protection against skin, food and other allergies in infancy and later in life. Food allergies are a growing food safety and public health concern, according to the U.S. Centers for Disease Control and Prevention (CDC). The CDC’s food allergy fact sheet estimates 8% of children in the United States have a food allergy. That’s 1 in 13 children, or about two students per classroom.

Longtime Seattle lactation consultant Catherine Fenner, IBCLC, says she’s been sharing the breast milk-allergy reduction connection with expectant and new moms for years, but she’s always eager to share new information reinforcing that connection. She wants new parents to revel in the power of human milk: “We are still discovering all the work your milk is doing behind the scenes to help your baby grow. Research is on-going, and mind-blowing discoveries are made all the time.”  

It comes down to micro-ribonucleic acids

In their research, study authors looked at micro-ribonucleic acids (also called miRNAs, they are the tiny molecules that regulate gene expression throughout the body) present in breastmilk to determine if they might be responsible for protecting infants against allergies. They zeroed in on just four out of the nearly 1,000 different kinds of miRNAs in human breast milk based on prior research showing relationships between these specific miRNAs and certain allergic conditions. 

The study followed 163 mothers who planned to breastfeed their babies for at least four months from birth. They tracked how long each baby breastfed, and measured the miRNA composition of each mother’s breast milk over four months and then calculated the amount of specific miRNAs infants consumed based on reported breastfeeding patterns. They also measured the concentration of certain miRNAs in mothers’ milk samples. 

Study findings

At the end of the four month study period, 41 (25%) developed eczema 33 (20%) developed a food allergy and 10 (6%) had wheezing. That left 79 infants who did not develop allergies. 

Those 79 babies, researchers found, consumed greater amounts, on average, of a specific micro-ribonucleic acid, miR-375, through their mothers’ breast milk. The researchers also found that the tiny molecules of miR-375 increased throughout lactation and that mothers with a lower body mass index tended to have higher concentrations of it. 

One miRNA stands out

“The fact that miR-375 content increased during the course of lactation may explain why sustained breastfeeding has been associated with reduced [allergies],” Hicks told Science Daily. He noted that the greatest increase of miR-375 happened in the first month following birth, but that the upward trend continued between months one and four. Formula, he noted, does not contain human miRNAs.

How to increase miR-375: More study needed

The new study opens the door to future research. Hicks hopes to see other studies explore ways to boost miR-375 levels in breastmilk. And, since about 75 percent of babies receive at least some formula by 6 months of age, he said researchers should explore ways of adding miR-375 to formulas as a means of addressing the disparity that formula-fed babies are more likely to develop atopic conditions. The Penn State College study also suggests that while encouraging breastfeeding as a means of reducing allergies in kids is important, finding ways to educate parents on the connection between lower BMI and higher miR-375 levels may help reduce the risk of allergy development.

Another call or equity 

Bestsy Hoffmeister, a Seattle-area IBCLC lactation consultant,  said that studies like the one out of Penn State College remind her again and again “that breastmilk contains multitudes. The more we study it, the more unbelievable it seems.”

At the same time, Hoffmeister says, every new study on the benefits of breastfeeding is a reminder of the inequities that allow some parents to exclusively nurse for many months and others mere weeks due to the need to return to work.

“It speaks to the need of more paid parental leave, more support and resources for new families, so that nursing parents can have the time and help they need to establish breastfeeding and human milk feeding,” Hoffmeister says. “The more we find out about how much breastmilk protects human infants, including reducing the risk and impact of RSV and flu, the more I wish every family had the opportunity to feed human milk to their baby.”

“Just get started”

While the study suggests that nursing to four months and longer may help reduce the chances of childhood due to the increasing miR-375 levels in breastmilk over time, lactation consultant Catherine Fenner doesn’t like to pressure new parents with time frames for nursing:

“The take away for me is to encourage parents to just start nursing, and see where it goes. Even a small amount of your milk gives your baby physiological gifts that last for a lifetime,” she says. 

Her message to her clients is to take it one step at a time: “Don’t worry about how long you are supposed to nurse. Just get started.  Do it for as long as it works for your family. Every drop counts.  Seek out support and information before challenges arise.”

More at Seattle’s Child:

“Seattle-based breastfeeding resources”

About the Author

Cheryl Murfin

Cheryl Murfin is managing editor at Seattle's Child. She is also a certified doula, lactation educator for and a certified AWA writing workshop facilitator at