Peanut Allergy May Be Triggered by Breastfeeding

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April 3, 2001 -- Babies susceptible to severe peanut allergy may be at risk from the potentially dangerous allergen even before they're old enough to eat. That's because new research shows that enough protein from a small serving of peanuts can be transmitted through a mother's breast milk, and this exposure may possibly predispose or set up some nursing babies to later experience allergic reactions.

Just a tiny amount of peanuts in food or even handling peanuts can be potentially deadly to children and adults with severe peanut allergy. The number of people affected by peanut allergy has increased dramatically in recent years, and research suggests that children at risk for allergies who are exposed to peanuts at an early age have an increased chance of developing lifelong peanut allergy.

The lead author of the new study says that until now, breast milk was not considered a potential source of the type of early exposure that can lead to development of a peanut allergy.

According to Peter Vadas, MD, the conventional advice has been to avoid giving kids foods containing peanuts until after age 3 if parents or other family members have a history of asthma, allergies, or eczema.

"Now we have to modify that a little bit," says Vadas, of St. Michael's Hospital in Toronto. "Now we also must warn these mothers to do their best to try not to eat peanut products while nursing so as to avoid indirectly exposing their children." His study appears in the April 4 issue of the Journal of the American Medical Association.

In Vadas' study, 23 healthy lactating women expressed breast milk immediately before and at timed intervals after consuming about half a cup of dry roasted peanuts. The researchers examined the samples to determine how much protein from the peanuts and whether two peanut allergens were detectable in breast milk.

Nearly 50% of the women had peanut protein in their breast milk. The protein appeared within one to six hours of eating the nuts and disappeared quickly from the milk of most women. Both of the peanut allergens appeared in the milk.

"It's been known for some time that at least some of the foods that mothers eat are passed in the breast milk," says Scott H. Sicherer, MD, an assistant professor of pediatrics in the division of allergy and immunology at Mt. Sinai School of Medicine in New York.

He says the study adds another piece to the puzzle by showing that peanuts eaten by the mother can get into breast milk "in a form and a quantity that could potentially sensitize or cause reactions in nursing babies."

The new study is in agreement with the nutrition committee of the American Academy of Pediatrics, which recently began recommending that mothers whose babies are at high risk for food allergies or other types of allergies consider not eating foods containing peanuts while breastfeeding, according to Sicherer, who provided WebMD with an objective analysis of the study.

Another expert, Marc E. Rothenberg, MD, says it still remains to be proven if the amount of peanut protein found in breast milk is sufficient to sensitize infants to developing a peanut allergy.

"The levels, in an of themselves, are pretty high, and this could explain why people have peanut allergy. ... Peanut allergy often presents in the first year of life, and we often wonder why that is if they haven't had any exposure and have only been consuming breast milk or formula," says Rothenberg, who is section chief of allergy and immunology and an associate professor at Children's Hospital Medical Center in Cincinnati. "This shows that exposure could have been through the breast milk, and that is significant. It means mothers who are breastfeeding and who are concerned about allergies should watch their diet."

Rothenberg says one interpretation of the study is that it may be possible -- by completely avoiding peanuts in infancy and early childhood -- to avoid ever developing a peanut allergy, since it usually develops early, if at all. On the other hand, he says it's also possible that some slight exposure may be necessary to strengthen the immune system to fight off or lessen the effects of a peanut allergy attack.

If you are pregnant and considering breastfeeding or already are breastfeeding, ask your doctor if you should avoid peanuts.

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