So long as they don't have nut allergies themselves, pregnant women shouldn't be afraid that eating nuts might trigger allergies in their child, according to a large new study.
In fact, when women ate nuts more than five times a month during pregnancy, their kids had markedly lower risk of nut allergies compared to kids whose mothers avoided nuts, researchers found.
"The take-home message is that the previous concerns or fears of the ingestion of nuts during pregnancy causing subsequent peanut or nut allergy is really unfounded," Dr. Michael Young said.
Young is the study's senior author and an attending physician in allergy and immunology at Boston Children's Hospital.
He cautioned that pregnant women shouldn't start eating peanuts and tree nuts to prevent their children from developing nut allergies, however.
"Even though our study showed a reduction of risk, I really have to emphasize that the way our study was done only shows an association," he told Reuters Health.
He and his colleagues write in JAMA Pediatrics that between 1997 and 2010 the prevalence of peanut allergies tripled to 1.4 percent of U.S. children.
For the new study, the researchers used data from a national study of female nurses between the ages of 24 and 44 years old. Starting in 1991, the women periodically reported what they ate.
The researchers then combined information on the women's diets from around the time of their pregnancies with data from another study of their children.
In 2009 the women completed a questionnaire that asked whether their children had any food allergies. Of 8,205 children in the study, 308 had food allergies, including 140 who were allergic to peanuts or tree nuts.
Tree nuts include walnuts, almonds, pistachios, cashews, pecans, hazelnuts, macadamias and Brazil nuts.
Overall, the researchers found that eating nuts while pregnant was not tied to an increased risk of nut allergies among children. On the contrary, the more nuts women reported eating during pregnancy, the less likely their children were to have nut allergies.
About 1.5 percent of children of women who ate less than one serving of nuts per month during pregnancy developed nut allergies. That compared to about 0.5 percent of children of women who ate five or more servings per week.
In other words, kids whose mothers ate nuts most often had about a third of the risk compared to kids whose mothers ate nuts least often.
The exception was children of women who themselves had a history of nut allergies. In those cases, when women ate nuts five or more times a week during pregnancy, their children had about two and a half times the risk of nut allergies compared to the kids of allergic mothers who avoided nuts during pregnancy.
"Certainly this is reassurance that eating nuts during pregnancy will not increase your child's risk of allergy," Dr. Loralei Thornburg said. "In fact, it may be tied to a decreased risk of nut allergies."
Thornburg was not involved in the new study but is a high-risk pregnancy expert at the University of Rochester Medical Center in New York.
However, "if there is a strong family history at all or if the mother herself has any food allergy, then she should go talk to her physician, because there is not clear data on that," Dr. Ruchi Gupta said.
Gupta is an associate professor of pediatrics at the Northwestern University Feinberg School of Medicine in Chicago and an expert on food allergies and asthma.
In an editorial accompanying the new study, Gupta wrote that it will take additional studies and research to understand why a growing number of children are developing food allergies and how to prevent it.
"What I do like about the study is it adds evidence that mothers-to-be should eat whatever they wish and not worry that the consumption of certain foods will result in allergies," she said.