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Wednesday, May 16, 2012
Wayne Shreffler, MD, PhD
We sometimes forget that although food allergy is most common in young children, a growing number of adults are also affected. An estimated 4% of the U.S. adult population is food allergic – about 9 million of us. And while there is still much to learn about food allergies in adults, we know that there are some important differences that affect their management and that are shaping new research questions.
Adult food allergy is a mix of persistent and new onset disease. So the fact that food allergy in children has been becoming more common and more persistent is resulting in an increase of allergies in adolescents and adults as well.
Most food allergies, including many of those that are still common in adults, are diagnosed in children and persist into adulthood. Allergy to peanuts, tree nuts and perhaps sesame are good examples of this category. They are usually diagnosed in childhood, but become relatively more common food allergens for adults than allergies that are more often outgrown such as those to milk or wheat.
There are some allergies, however, that tend to be diagnosed more commonly in adults, though some of these may vary by diet. For example, Dr. Scott Sicherer found that in the U.S., estimates of allergy to fish were more than twice as high in adults than children (0.5% versus 0.2%) and allergy to crustaceans (like shrimp) was five times more common (2.5% versus 0.5%).
Cross reactions: pollen and food allergies
One very prominent group of food allergies that begins to grow in older children and continues to do so during adulthood are those specific to plant allergens that “cross react” to pollen allergens. In several surveys of food allergy, these are the most common adult food allergies.
The patterns and frequencies of these allergies can vary greatly with geography. The affected person first becomes allergic from exposure to airborne allergens (e.g. Birch pollen), which then results in allergic symptoms from eating plant foods that contain related allergens. For example, Birch-allergic individuals may develop reactions to related groups of nuts and fruits (e.g. almonds, apples, pitted fruits, hazelnuts). This is called “oral allergy syndrome” because symptoms are usually limited to the mouth and throat. It is usually caused only be fresh forms of the food.
People with oral allergy syndrome should see an allergist because reactions can be significant and could be confused or overlap with other food allergies. New blood tests are being evaluated now that may help to sort out in some of these cases when a person is at risk for more severe reactions.
Adult reactions may be more severe
Outside of oral allergy syndrome, which is not associated with anaphylaxis, there is some evidence that reactions in adults tend to be more severe. Some factors we know of that can influence severity include:
These are factors that should be considered by patients together with their physicians in the management of their allergies in the context of their overall health.
Finally, as in food allergy generally, there is still much that we need to learn that will help us find new prevention and management strategies and give insight into new therapies. We know that becoming allergic to multiple airborne allergens, especially pollens, is a risk factor for developing oral allergy syndrome. But we do not know much about the risk factors for adult onset allergy – especially those food allergies that are likely to be unrelated to cross reactivity to airborne allergies.
It seems likely that regular consumption of a particular food would lower the chance it would come to be recognized as an allergen as an adult and that having a food allergy as a child would increase the likelihood of adult onset food allergy, but there are no data that I am aware of to address these fundamental questions.
Additional gaps in our knowledge include things like the true prevalence of eosinophilic gastrointestinal food allergies, in particular eosinophilic esophagitis, and the effectiveness of interventions like oral immunotherapy in adults with food allergies. In addition, there are adults with highly specific and reproducible symptoms limited to the gastrointestinal tract, many of whom likely have non allergic forms of food intolerances, but some of whom we may eventually learn have true food allergies.
Fortunately, more attention is being brought to adult food allergy by groups like the Food Allergy & Anaphylaxis Network and academic thought leaders around the world. Several new research studies of interventions and diagnostics, including some here at the Mass General Food Allergy Center, are targeting adults along with pediatric populations, and the future holds promise for addressing many of these important questions.
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