June 20, 2011 -- The largest study ever to track childhood food allergies in the U.S. shows that they may be more common and more dangerous than previously recognized.
The study, a detailed survey of families with at least one child younger than 18, shows that 8% of kids under age 18 are allergic to at least one food. Surveys for about 38, 000 children were completed.
Previous studies, including a government survey published in 2009, had pegged that number at around 4%.
Allergies to peanuts were the most commonly reported, affecting 2% of kids. Milk and shellfish allergies ranked second and third. Tree nuts, egg, fin fish, strawberry, wheat, and soy rounded out the top nine food triggers.
"This study shows that there's a very high, and higher than we thought, prevalence of food allergy in the U.S." says Susan Schuval, MD, pediatric allergist at Cohen Children's Medical Center in New Hyde Park, N.Y., who was not involved in the study.
"We see this in our clinic," Schuval says, "tons and tons of food allergies."
Many food allergies in children are mild and fade over time. But in other cases, reactions to food can be dangerous and even deadly.
The new study offers one of the first estimates of these severe reactions in children, showing that 40% of kids with food allergies experience severe symptoms such as wheezing and anaphylaxis, which is characterized by difficulty breathing and a sudden drop in blood pressure.
"I don't think people quite understand food allergy," says study researcher Ruchi S. Gupta, MD, MPH, an assistant professor of pediatrics at Northwestern University's Feinberg School of Medicine in Chicago. "It could be something that's life-threatening. It could cause death."
The study found that food allergies were highest in preschoolers, peaking between 3 to 5 years of age.
Teenagers, however, particularly boys, were most likely to experience severe, life-threatening reactions.
"More fatalities occur in teenagers and older children," Gupta says. "They're going out with their friends and they don't want to feel different. They may not ask the ingredients in everything, you know, at a restaurant, in front of people."
Independent experts praised the scope of the new study, which is published in the journal Pediatrics.
"This is a very significant study since accurate data on the prevalence of food allergy are lacking," says Robert Wood, MD, director of pediatric allergic and immunology at Johns Hopkins University School of Medicine, in Baltimore, in an email to WebMD.
Tracking Food Allergies in Kids
Because the study was so large, researchers weren't able to use clinical measures, like blood tests or medical records to count allergy cases.
Instead, they relied on parents to report either a doctor's diagnosis or classic symptoms.