NEW YORK (Reuters Life!) - Schools may have a good reason for banning nuts from the classroom and canteen with a U.S. study finding the number of children allergic to peanuts and tree-nuts may be rising.
Researchers from the Mount Sinai School of Medicine in New York found that between one and two percent of children in the United States may have allergies to peanuts or tree nuts, with rates seemingly tripling since 1997.
A similar study in Canada by McGill University in Montreal came up with similar rates of allergies but had no previous data to see if the numbers were on the rise.
Peanuts and tree nuts such as almonds and walnuts are the most common causes of severe, sometimes life-threatening allergic reactions to food in the United States.
Recent research has suggested that while the percentage of children with these allergies remains relatively low, rates may be on the upswing, although no one is sure why these allergies may be on the rise.
Some researchers suspect the so-called "hygiene hypothesis" may be contributing to allergies more generally as today's clean living createsg less exposure to germs from early life on and may impact the immune system.
But Scott Sicherer from Mount Sinai School of Medicine said one hypothesis has to do with how peanuts are processed. In roasted form peanuts may be more likely to trigger allergies.
"The current results highlight the need for more research on food allergy prevention and treatment strategies," he said.
"The study is unique because we used the same (survey) methods three times over an 11-year period and assessed specific food allergies in the general U.S. population. Nothing like this has been done before," Sicherer told Reuters Health.
Sicherer and his team found that among 5,800 households surveyed in 2008, 1.4 percent of children younger than 18 had a peanut allergy, based on parents' reports.
That was triple the rate the same researchers found in a comparable survey done in 1997.
A Canadian study of more than 3,600 households surveyed in 2008 and 2009 found a somewhat higher rate -- with 1.7 percent of children having a "probable" peanut allergy. Similar patterns were seen with allergies to tree nuts.
In the U.S. survey, 1 percent of children were reported to have tree-nut allergies, up from 0.2 percent in 1997, while in the Canadian study 1.6 percent of children were considered to have probable tree-nut allergies. Allergies were considered "probable" when parents reported a "convincing" history of allergy symptoms -- such as a rash, hives, swelling or wheezing within two hours of their child having the suspect food -- or when they said a doctor had diagnosed the problem.
The Canadian researchers also tried to confirm the reported allergies by asking participants for permission to contact their doctors. However, many refused to give it, and even when they did, the doctors often failed to provide the test results.
As a consequence, the rates of "confirmed" allergies in the study were lower. Just 1 percent of children had a confirmed peanut allergy. Among adults, the rate of probable peanut allergy was 0.7 percent, while the rate of confirmed cases was under 0.3 percent.
"We think the 'probable' prevalence is probably more reflective of the true prevalence," researcher Dr. Moshe Ben-Shoshan told Reuters Health.
Ben-Shoshan said the study was the first to look at the national rate of potentially severe food allergies in Canada so it was unclear whether - as in the U.S. study - some allergies might be on the rise there.
Both studies are published in the Journal of Allergy & Clinical Immunology (here(10)00537-3/abstract).
Reporting by Amy Norton of Reuters Health, Editing by Belinda Goldsmith