July 2014 Issue
Food Allergy Sensitization — New Study Finds Geography Plays a Role
By Sherry Coleman Collins, MS, RDN, LD
Vol. 16 No. 7 P. 12
When it comes to allergies, there seems to be no escape for those who are predisposed to developing them, according to a recent study that examined the prevalence of allergic sensitization across the United States using data from the National Health and Nutrition Examination Survey (NHANES) 2005-2006. The study, which includes 10,348 participants, found that the overall prevalence of allergic sensitization doesn’t differ from region to region in the United States, although sensitization to specific allergens and allergen types shows regional variation.1
The research shows that 44.6% of Americans aged 6 and older had positive test results for serum immunoglobulin E (IgE) antibodies for at least one of 19 allergens, with 16.2% having positive serum IgE tests related to at least one of four foods tested (egg, cow’s milk, shrimp, and peanut). The study also found that 36.2% of children aged 1 to 5 were sensitized to at least one allergen, such as dust, pollen, or food, and that the prevalence of food sensitization was significantly higher in 28% of children under the age of 6.1
Researchers suggest that individuals predisposed to developing allergies will become allergic to something in their environment or to food, regardless of where they live. Furthermore, they found that while allergic sensitization rates are about the same no matter where people lived in the United States, differences existed among the types of allergens that caused reactions.
It’s important for RDs to know that the location in which potentially food allergic clients live may influence the type of food allergy they develop. Practitioners also should be alert to a client’s or patient’s reported symptoms consistent with food allergies, which can vary from mild to severe and include gastrointestinal symptoms such as nausea, vomiting, and diarrhea and respiratory and skin reactions.
Food allergies often are overlooked and may be misdiagnosed, but RDs can play an important role in helping clients at risk get properly diagnosed and educated to manage their allergy.
Sensitization vs. True Allergy
Sensitization and true allergy aren’t the same. “Although allergic sensitization is a major risk factor for allergic disease, it is not synonymous with allergic disease,” says Päivi Salo, PhD, lead author of the NHANES study and a researcher in the Environmental Cardiopulmonary Disease Group in the National Institute of Environmental Health Sciences’ division of intramural research. “Assessment of allergen-specific IgE antibodies with serologic analyses—or skin test challenges—confirms allergic sensitization, whereas subject’s clinical history and physical examination remain important cornerstones of the diagnosis of allergic disease.” Moreover, an individual can be sensitized to a substance or food yet never manifest a clinical allergic reaction.
Skin prick tests and serum blood tests check for IgE antibodies to specific proteins. Positive tests indicate that sensitization has occurred. The more drastic the positive result, as evidenced by a larger wheal size (the large red bump that appears at the site of the skin prick) or higher numbers of IgE antibodies in the blood, the more likely an individual has a true allergy. However, it’s important to recognize that false-positives are common, occurring in up to 60% of blood tests and skin prick tests.2
Oral food challenges are the gold standard for diagnosing food allergies, but “they tend to be time consuming, expensive, and subject study participants to potentially severe allergic reactions [which isn’t feasible in large-scale studies],” Salo says. Some physicians, patients, and parents are hesitant to perform and undergo oral food challenges, but a food allergy diagnosis is life altering, so ensuring its accuracy should be paramount.
Recent research has shown that allergic individuals experience an improved quality of life when they undergo oral food challenges to test for tolerance, even those who have an allergic reaction to the food allergen and fail the oral food challenge.3 Therefore, people who have a low risk of anaphylaxis should be encouraged to participate in oral food challenges to help ensure an accurate diagnosis and also determine if and when they will or have outgrown a food allergy.
Where You Are and What You Eat
According to the NHANES study, individuals in the South were more likely to develop allergies to eggs, cow’s milk, shrimp, and peanuts.1 Researchers don’t know why allergy rates to these foods are higher in the South than in other areas. Salo says the study wasn’t meant to identify a causal relationship between allergy and geography, so further research is needed.
In support of geographic influences on allergic sensitization, an international study by Dalal and colleagues highlighted the prevalence of sesame allergy in Israel and differences in the types of food allergies among allergic individuals living in various countries.4 In this study, researchers identified eggs as the top allergen for five of seven countries (Australia, France, Israel, Japan, and Spain), but there were great variations among the allergenic foods that ranked highest from country to country. Italy’s top food allergen is fish, while Singapore’s is bird’s nest (an ingredient commonly eaten as a regional delicacy).4 Other allergens include various fruits, vegetables, lentils, nuts, wheat, and mustard.
Since sensitization results from exposure to specific proteins, researchers say it makes sense that these foods reflect the diet of the individuals in a certain region or country, and that individuals won’t develop allergies to foods they’ve never eaten.
Oral Allergy Syndrome, Cross-Reactivity, and Clustering
Just as the substances people are allergic to vary country by country, so do the triggers that cause allergic reactions and the ways in which people respond to the allergens. Individuals may respond to allergens by developing oral allergy syndrome or through cross-reactivity or clustering.
Oral allergy syndrome is a condition in which an individual who’s allergic to certain pollens (eg, birch tree pollen) will experience itching and swelling in the oral cavity after eating raw fruits and vegetables. Typically, cooked vegetables and fruits aren’t an issue. “It’s unknown what really triggers an allergic response and cross-reactivities, particularly in the case of oral allergy syndrome,” says Soheila Maleki, PhD, lead research scientist for USDA Food Allergy Research. “Similarities in proteins of inhalant allergens [eg, dust mites] and food allergens indicate that there could be potentially similar triggers for most food allergies.” In fact, disagreement exists among experts about whether oral allergy syndrome represents a true food allergy or is simply a false reaction to similar proteins.
Cross-reactivity is unpredictable among individuals, but patterns exist. For instance, people who are allergic to cockroaches and dust mites are more likely to be allergic to shrimp. Likewise, those allergic to birch tree pollen may be at higher risk of a peanut allergy. Moreover, approximately one-third of people who have a peanut allergy also are allergic to tree nuts.
Clustering occurs when a person who’s sensitized to one allergen in a group of similar entities is more likely to be allergic to something else within the group. “Allergies tended to aggregate in groups of allergens that were similar,” Salo says of her NHANES study. “In NHANES 2005-2006, the 19 allergen-specific IgEs grouped into seven clusters. This suggests that a person who’s sensitized to one allergen in the cluster is more likely to be allergic to another allergen in this cluster. For example, people sensitized to cats were more likely to be allergic to dogs, and those who were sensitized to a plant-related allergen were more likely to be allergic to other plant-related allergens and so forth.”
As new research emerges, it will provide additional information to expand the body of knowledge about food allergies, diagnosis, and management. Thus far, the medical community knows that sensitization isn’t the same as a true allergy, and nutrition professionals can play an important role in helping clients and patients understand the difference. In fact, the prevalence of true food allergy is significantly less than the prevalence of sensitization, according to the new NHANES study. Researchers estimate that the prevalence of true food allergy is up to 8% in children and less than 4% in adults.5,6 Geography plays a role in the type of allergy individuals develop, possibly due to the differences in environmental and dietary factors, as well as cross-reactivity and clustering.
“RDNs should be more aware of the potential for allergies in their patients,” says Kate Scarlata, RDN, LDN, a digestive disorders expert and the author of The Complete Idiot’s Guide to Eating Well With IBS. “Since allergies in children seem more prevalent in metropolitan areas and in our southern states, RDNs working with patients in these areas should be even more vigilant in noting symptoms that may indicate an allergic reaction and refer patients to allergists for appropriate work up.” Practitioners should be familiar with recognizing signs and symptoms of food allergies and be prepared to assist clients with education and referrals to improve patient care.
— Sherry Coleman Collins, MS, RDN, LD, is a private practitioner in Atlanta specializing in food allergies and sensitivities, digestive disorders, and nutrition communications.
Since individuals may outgrow food allergies, it’s important for clients and patients to see an allergist regularly for reevaluation.
To determine the status of a patient’s allergy, an allergist may administer a skin prick or blood serum immunoglobulin E test. Based on the size of the wheal (the red bump that surfaces on the skin indicating sensitization), blood test results, and other diagnostic criteria, the physician will determine whether a true allergy persists.
If the physician believes the patient is at low risk of a serious reaction, he or she may conduct an oral food challenge. Because of the potential for a serious and life-threatening reaction, oral food challenges always should be conducted in an allergist’s or physician’s office. Previous reactions don’t guarantee how mild or severe future reactions will be, and variations may occur from reaction to reaction and between allergic individuals. Even patients who have experienced mild allergy symptoms may experience anaphylaxis. Therefore, those who undergo an oral food challenge typically remain under medical supervision for two hours after ingesting the allergenic food, although reactions may occur several hours after the food has been eaten.
1. Salo PM, Arbes SJ, Jaramillo R, et al. Prevalence of allergic sensitization in the United States: Results from the National Health and Nutrition Examination Survey (NHANES) 2005-2006 [published online February 9, 2014]. J Allergy Clin Immunol. doi: 10.1016/j.jaci.2013.12.1071.
2. Blood tests. Food Allergy Research & Education website. http://www.foodallergy.org/diagnosis-and-testing/blood-tests. Accessed April 27, 2014.
3. Franxman TJ, Howe LE, Greenhawt MJ. Oral food challenge and food allergy quality of life in caregivers of food allergic children. J Allergy Clin Immunol. 2013;131(2 Suppl):AB57.
4. Dalal I, Binson I, Reifen R, et al. Food allergy is a matter of geography after all: sesame as a major cause of severe IgE-mediated food allergic reactions among infants and young children in Israel. Allergy. 2002;57(4):362-365.
5. Gupta RS, Springston EE, Warrier MR, et al. The prevalence, severity, and distribution of childhood food allergy in the United States. Pediatrics. 2011;128(1):e9-e17.
6. NIAID-Sponsored Expert Panel, Boyce JA, Assa’ad A, et al. Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-sponsored expert panel. J Allergy Clin Immunol. 2010;126(6 Suppl):S1-S58.