Nut allergies on the rise

Peanut and tree nut (almonds, brazil nuts, macadamias, walnuts, pecans, pistachios, cashews, and hazelnuts) allergies share similar characteristics and co-existing allergies are quite common. Most peanut/tree nut allergies begin in early childhood and about 80 to 90% of these persist into adulthood.

Understanding allergies

A true food allergy (rather than an intolerance or sensitivity) results when a component of a food (usually a protein) triggers the release of substances like histamine that cause symptoms ranging from itching, rash, or runny nose to more serious reactions, including throat swelling and difficulty breathing.

These reactions require prior sensitization, meaning that the person must have been exposed to the substance before the onset of allergic symptoms. Sometimes, the person has no knowledge of prior exposure. In these cases, exposure could have been from the environment (breathing in some particles of the food, for example) or, potentially, in utero from the mother’s diet.

Mum + nuts = fewer child allergies

The new study investigated the diets of mothers around the time of their pregnancies and the subsequent development of peanut and tree nut allergies in their children. They found:

• Of 8,205 children in the study, 140 were diagnosed with a peanut or tree nut allergy.
• Children of mothers without a nut allergy, who ate the highest amount of nuts (five or more servings per week) around the time of their pregnancies were 69% less likely to develop nut allergies during childhood than those born to mothers who ate the least amount of nuts (less than one serving per month).
• Children born to mothers with a peanut or tree nut allergy were more likely to develop a nut allergy if their mothers ate peanuts or tree nuts around the time of pregnancy.

Revisiting the recommendations

For years, paediatricians have recommended that parents delay introducing peanuts and tree nuts until children are three years old, to decrease the chance of allergy. However, while some studies have shown that avoiding these foods may decrease allergy risk, others have shown the opposite: that delaying the introduction of highly allergenic foods may increase the risk of food allergy.

“Our study supports the hypothesis that early allergen exposure increases the likelihood of tolerance and thereby lowers the risk of childhood food allergy,” said lead study author, Dr. Michael Young of Boston Children’s Hospital, adding “our data support the recent decisions to rescind recommendations that all mothers avoid peanuts and tree nuts during pregnancy and breast-feeding.”

These recommendations go for other foods, too. According to the American Academy of Asthma, Allergy, and Immunology, “There are no current data available to suggest that cow’s milk protein (except for whole cow’s milk), egg, soya, wheat, peanut, tree nuts, fish and shellfish introduction into the diet need to be delayed beyond four to six months of age.”

(JAMA Paediatrics;doi:10.1001/jamapaediatrics.2013.4139)