Dr. Peter Vadas
, who led the study as director of allergy and clinical immunology at the University of Toronto
, said women who have a family history of allergies should avoid eating peanuts while nursing.
An estimated 1.6 million Americans , including 1 in 100 preschool-age children , are allergic to peanuts , the researchers said.Reactions 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.
The researchers analyzed breast milk from 23 nursing women after they had eaten a half-cup of peanuts.
About 80 percent of susceptible children develop an allergic reaction after their first known sampling of peanut products , Vadas
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.
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 summer , the academy said that because potential allergens have been found in breast milk , nursing mothers of susceptible infants should avoid eating peanuts.