Boy eating peanut butter.

It's now thought that early exposure to allergens like peanuts may increase tolerance and lower risk of a childhood food allergy. (iStock)

Children seem to be at lower risk for peanut and tree nut allergies if their moms ate more nuts while pregnant, a finding that researchers say reinforces recent Canadian advice not to avoid peanuts in pregnancy for women who can eat the protein source.

Earlier this month, the Canadian Paediatric Association concluded there's no evidence that avoiding milk, eggs, peanuts or other potential allergens during pregnancy helps to prevent allergies in children, but that the risks of undernutrition for the mother and potential harm to the infant may be significant.

In Monday's online issue of the journal JAMA Pediatrics, researchers set out to clarify by examining the records of more than 8,000 children born to women participating in the ongoing Nurses Health Study II on diet and health habits.

Dr. Michael Young of Boston Children's Hospital and his co-authors identified 308 cases of any food allergy, including 140 allergies to peanuts or tree nuts such as walnuts, almonds, pistachios, cashews, pecans, hazelnuts, macadamias and Brazil nuts.

Of the children allergic to nuts, 50 had mothers who were allergic to nuts, and 82 did not.

If a mother ate peanuts or tree nuts five or more times a month, the risk of of her child developing a nut allergy was lowered, the researchers found. That was not the case among children of mothers who were allergic to peanuts or tree nuts themselves.

"Our study supports the hypothesis that early allergic exposure increases tolerance and lowers risk of childhood food allergy," the study's authors concluded.

The study can't prove a cause-and-effect relationship. For example, mothers who ate more nuts were also more likely to consume fruits and vegetables that are high in antioxidants. The researchers said it's possible that higher exposure to antioxidants in the womb offers protection against food allergies rather than the nuts themselves.

Curb cravings with peanut butter

The study only looked at maternal history, which Young said seems to be more relevant to allergy heredity than nut allergies in fathers.

Two pediatricians independently examined the medical records and allergy skin test results to confirm allergy cases and remove false positives such as lactose intolerance.

Food allergy affects one in 13 children in the U.S. and nearly 40 per cent of those affected have a history of severe, potentially life-threatening reactions, Dr. Ruchi Gupta of Northwestern University in Chicago said in a commentary in the journal.

Once doctors have a better understanding of why, they'll be able to give more specific preventive recommendations, she said.

"For now, though, guidelines stand: pregnant women should not eliminate nuts from their diet as peanuts are a good source of protein and also provide folic acid, which could potentially prevent both neural tube defects and nut sensitization. So, to provide guidance in how to respond to the age-old question 'To eat or not to eat?', mothers-to-be should feel free to curb their cravings with a dollop of peanut butter!" Gupta concluded.

The study was funded by Food Allergy Research and Education, a New York-based nonprofit group that advocates for people with allergies and gets some funding from industry sources. It had no role in designing or running the study. Young has received royalties from a book on peanut allergies.

With files from The Associated Press