New research suggests that women who breast-feed after eating peanuts could potentially trigger an allergic reaction in susceptible babies.
"This is the first study to demonstrate that peanut protein is transferred from the maternal diet into the breast milk of lactating women," said Dr. Peter Vadas, director of allergy and clinical immunology at the University of Toronto and the study's lead author.
The findings appear in Wednesday's Journal of the American Medical Association.
Reactions to peanuts can range from hives to life-threatening anaphylaxis, which may involve sudden low blood pressure, extreme swelling and difficulty breathing.
While deaths from food allergies are rare, experts think peanut allergies are on the rise and peanut protein is an especially potent allergen. Vadas said it's less apt than other foods to break down during processing or digestion.
About 80 percent of susceptible children develop an allergic reaction after their first known sampling of peanut products, he said. But typically for an allergic reaction to occur, the body must have previously been exposed to the allergen and had time to build up the antibodies that help trigger allergy symptoms.
The study suggests that in some cases the initial exposure may occur during breast-feeding. Vadas said peanuts should thus be avoided by nursing women with at-risk infants -- those with a strong family history of any allergies or who have a parent or sibling with a peanut allergy.
The authors analyzed breast milk from 23 nursing women after they'd eaten about a half cup of peanuts. Peanut protein was found in samples from 11 women within up to six hours of eating peanuts.
Co-author Dr. Wesley Burks of Arkansas Children's Hospital said the findings explain allergic reactions such as hives that have occurred in nursing infants whose mothers had eaten peanuts. Infants of mothers in the JAMA report weren't studied.
The American Academy of Pediatrics encourages new mothers to breast-feed for at least a year and says food allergies are more common in formula-fed babies. But in a policy statement last August, the academy said that because other potential allergens have been found in breast milk, nursing mothers of at-risk infants should avoid eating peanuts.
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