Oct. 20, 2010 -- About three of every 100 people in the U.S. have at least one food allergy, and the presence of a food allergy may raise their risk of asthma, a study shows.

The study, which appears in the October issue of Journal of Allergy and Clinical Immunology, is the largest to offer a national snapshot of food allergy prevalence.

Children are at greater risk for food allergy than adults, and black male children are particularly at risk, the study shows.

"This gives us a good perspective, and the prevalence number is pretty solid," says study researcher Andy Liu, MD, an allergist at National Jewish Health in Denver.

Food allergies are on most everyone's radar screen these days with growing numbers of schools calling themselves "peanut-aware" or "peanut-free" and parents routinely asked to provide information on their child's food allergies.
Food Allergies on the Rise?

Researchers are not sure if there has been an actual rise in food allergies because they lack background data.

"There has been some suggestion that the rate of food allergy has been increasing, and it may be," Liu says. "There is certainly more awareness. And many of us, when think back to when we were in school, we didn't hear about food allergy."

Liu tells WebMD that when he was charged with bringing in snacks for his son's kindergarten class, he was stunned to learn that six of 28 kids had registered food allergies.

"Schools have moved to a position where they are taking food allergy seriously," he says. "Families were treated as pariahs before and were told to look for other school options if they had children with food allergies."

Researchers analyzed data on 8,203 people, ranging in age from 1 to older than 60, who completed the National Health and Nutrition Examination Survey in 2005-2006. Participants also had blood tests to confirm the presence of four food allergies: peanut, milk, egg, and shrimp. Among people with food allergy, 1.3% were allergic to peanuts, 0.4% were allergic to milk, 0.2% had and egg allergy, and 1% were allergic to shrimp, the study shows.
Food Allergy-Asthma Link

The study shows that people with food allergies were 3.8 times more likely to have asthma than those without food allergies. Food allergy also appeared to be a marker for asthma severity. People with a food allergy were about seven times as likely to have landed in the emergency room for an asthma attack in the year before the study as people without food allergies.

Exactly how food allergy and asthma are connected is not fully understood, but the link appears to go both ways. "People with food allergies are more likely to have severe asthma attacks -- and that link is one that we have suspected. But to see it in a national study helps confirm it," Liu says. "If you have asthma, look into food allergies and if you have food allergy, discuss your asthma risk with your allergist."

Carla Davis, MD, an assistant professor of pediatrics-allergy and immunology at Baylor College of Medicine in Houston, says that it is impossible to tell if food allergies are on the rise based on this study.

What we can tell, she says, is that "being a child is a risk factor for having food allergy and the prevalence in children is higher than in adults." This could be because children tend to grow out of certain food allergies.

For example, "milk and egg allergy can be transient, but peanut and shrimp allergy persist through adulthood," she says.

"Parents should be aware that if a child has symptoms such as hives, lip swelling, cough, difficulty breathing, feeling faint, or severe, repetitive diarrhea and/or vomiting that occur within 15 to 20 minutes of eating a food, they could be symptoms of food allergy and should be evaluated by a physician," she says.

Additionally, "people with food allergy and asthma should make sure asthma is under control because asthma is likely to be more severe in the face of food allergy," she says.