Peanut, tree-nut allergies may be on the rise in kids

Between 1 and 2 percent of children in the U.S. and Canada may have allergies to peanuts or tree nuts, with the U.S. rates seemingly on the rise, two new studies suggest.

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 U.S. Recent research has suggested that while the percentage of children with these allergies remains relatively low, rates may be on the upswing.

In the new U.S. study, researchers 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.

The 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. Meanwhile, 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 2 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 less than 0.3 percent.

"We think the 'probable' prevalence is probably more reflective of the true prevalence," lead researcher Dr. Moshe Ben-Shoshan, of McGill University in Montreal, told Reuters Health.

The study is the first to look at the national rate of potentially severe food allergies in Canada, according to Ben-Shoshan. So it is 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.

The U.S. study adds to evidence that peanut allergies may be more common among kids now than a decade or two ago. But it also squares with a research review published last week in the Journal of the American Medical Association (JAMA) finding that estimates of the true rate of food allergies - and whether they are increasing - have been hampered by a "lack of uniformity for criteria" for diagnosing such allergies.