Australian researchers say they've found a possible cause for nut allergies, and it's likely to get lactation experts a bit riled up.

Investigators at the Australian National University claim that children who are exclusively breastfed for their first six months have a greater risk for developing a nut allergy than those given other foods or fluids, either exclusively or in combination with breast milk.

"These results contribute to the argument that breastfeeding by itself does not appear to be protective against nut allergy in children, and that it may in fact be causative of allergy," they wrote in the International Journal of Pediatrics.

To explore the possible connection, the researchers analyzed more than 15,000 questionnaires answered by parents of kids entering kindergarten across Australia. The parents replied to questions about whether their kids were allergic to peanuts or other nuts. Respondents also indicated what they fed them in their first six months.

Overall, the researchers found the likelihood for developing a nut allergy was one and a half times higher in breast-fed children than in those not breastfed. According to the researchers, this replicated their previous findings, which also drew a link between breastfeeding and subsequent nut allergies.

But outside experts say that the connection is far from clear. "I am not aware of studies saying that breastfeeding per se causes a nut allergy," said Dr. Scott Sicherer, a professor of pediatrics at the Jaffe Food Allergy Institute at the Mount Sinai School of Medicine in New York.

"In my opinion, none of the studies that the authors quote as implicating breastfeeding as 'a cause of the increased trend in nut allergy' actually do so," he continued, noting there are many possible variables, including genetic predispositions.

Other food allergy experts were even more critical.

"The conclusions drawn do not match the results of the study, therefore the implications that [the lead researcher] has been discussing are ridiculous and inappropriate," Dr. Katie Allen, a pediatric gastroenterologist and food allergy researcher at the Murdoch Children's Research Institute in Australia told the Australian site ABC Science.

According to the Centers for Disease Control and Prevention, in 2007 about 3 million children, age 18 or younger, had food or digestive allergies; these occur when the immune system mistakenly targets something as harmful, causing an abnormal response to a food. Among children with food allergies, peanut allergies have been the most common, followed by allergic reactions to milk and shellfish. The exact cause of the allergies is unknown.

One problem with the current study, according to Sicherer, is that it does not necessarily address the question of "reverse causation."

"Mothers of infants [might] have been told that breastfeeding [protects against allergies] because early studies showed that compared to having formula, infants [who were] breastfed had [fewer] allergic skin rashes and milk allergies," he said. Sicherer said that mothers may have been inclined to exclusively breastfeed their children for longer periods after seeing rashes in an attempt to protect them, thereby making it appear to researchers as though longer stretches of breastfeeding were tied to increased allergy risk. But really, it may have been the allergic signs that prompted certain moms to breastfeed longer, he said.

Far better established are some of the health benefits of breastfeeding; the practice has been shown to provide babies with key nutrients as well as antibodies to help fight disease.

"Talk to your doctor," Sicherer said. "There are some differing opinions on when to start giving complementary foods to an infant, 4 to 6 months [old], but not much controversy that 'breast is best' for many reasons." The World Health Organization recommends exclusively breastfeeding a new baby for as long as six months.


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