May 11, 2010 -- Food allergies are common, especially among children, but it is not clear just how common they are because there is no generally accepted definition for them, a review of past studies finds.
Researchers say the lack of an accepted definition and evidence-based guidelines for diagnosing food allergies has hindered efforts to determine their prevalence and evaluate new treatments.
The review appears in the May 12 issue of the Journal of the American Medical Association.
“Right now there are just too many different definitions of what food allergies are,” study researcher Jennifer J. Schneider Chafen, MD, of the VA Palo Alto Healthcare System tells WebMD. “A true food allergy can be life threatening, but many people who just can’t tolerate a particular food are told they have food allergies.”
Food Allergies Can Be Deadly
Milk, eggs, peanuts, tree nuts, fish, shellfish, soy, and wheat are the most common foods associated with allergic reactions.
These eight foods account for about 90% of all food-related allergic reactions, according to the Food Allergy & Anaphylaxis Network.
While children often outgrow allergies to many of these foods, allergic reactions to peanuts and shellfish tend to be lifelong.
When food allergies are severe enough to cause an anaphylactic reaction, death can occur.
College student Matt Mitchell, who is now 20, has had several close calls due to a lifelong milk allergy.
And just last month, he ended up in the ER after eating another food with trace amounts of milk, his mother, Lynda, tells WebMD.
“I call milk allergies the Rodney Dangerfield of food allergies,” she says. “They don’t get the respect that peanut allergies get because most people confuse them with lactose intolerance. But just like peanuts or shellfish, a milk allergy can be life threatening.”
Food Allergy Prevalence Unclear
The newly published review of 72 studies was funded by the National Institute of Allergy and Infectious Diseases (NIAID).
The federal agency is expected to release evidence-based guidelines for diagnosing food allergies late this summer, according to Schneider Chafen.
“Having a basic framework for diagnosing food allergies will help us better interpret studies evaluating diagnosis and treatment,” she says.
According to the review, between 1% and 10% of people in the U.S. have food allergies.
While individual studies suggest an increase in allergic food reactions, this could not be confirmed.
Among the other review highlights:
- The safety and effectiveness of immunotherapy for desensitizing patients to food allergies remains unknown. The treatment involves a challenge with minute amounts of the allergen.
- Probiotics in conjunction with breastfeeding, hypoallergenic formula, or both might help prevent food allergies in high-risk infants, but the independent impact remains uncertain.
- Skin prick testing, blood testing, and food challenges all play a role in diagnosis, but all also have their drawbacks.
Skin Prick, Blood Test Often Unreliable
Food challenge in a physician’s office or hospital setting is the most reliable way to confirm a specific food allergy, but such testing is costly, time consuming, and can result in anaphylaxis.
Because of this, most food allergies are diagnosed through skin prick or blood testing alone, which often leads to overdiagnosis.
“Children who come to see me often leave with fewer food allergies than they came in with,” pediatric food allergy specialist Todd David Green, MD, of Children’s Hospital of Pittsburgh tells WebMD.
In the absence of other indicators like a strong family history of food allergies, Green says skin prick and blood tests should not be relied on alone to confirm a food allergy.
Lynda Mitchell, who is president of the advocacy and education group Kids with Food Allergies, agrees.
“We tell parents that about half the time a skin prick or blood test may not be accurate and that patient history, physical examination, and other factors need to be considered,” she says.
Mitchell says overdiagnosis of food allergies is common and can be devastating for a family.
She cites the case of a Minnesota 3-year-old who had been fed highly specialized formula through a tube in his stomach since he was a baby because his food allergies were thought to be so severe.
Extensive evaluation at Denver’s National Jewish Hospital, which runs one of the nation’s top pediatric food allergy programs, revealed no allergic reaction to more than a dozen previously suspect foods.
“The child was able to eat Thanksgiving dinner with his family,” she says.