Study Suggests Genetic and Environmental Factors May Play a Role in Higher Allergy Rate
By Salynn Boyles
WebMD Health News
Reviewed by Laura J. Martin, MD
Sept. 6, 2011 -- African-American children in the U.S. have a higher rate of food allergies than children of other races, and new research suggests that genetic and environmental factors may explain why.
Researchers found self-reported black race to be associated with a higher risk for all food allergies examined. Genetically verified African ancestry was significantly linked to peanut, but not milk, allergies.
The study is published in Pediatrics.
The findings highlight the potential pitfalls of relying on self-reported race when examining racial disparities in disease, says pediatric allergist and researcher Rajesh Kumar, MD, MS, of Children's Memorial Hospital, Chicago.
The findings also confirm previously reported racial differences in the prevalence of food allergies in children and teens. But more research is needed to understand how genes and the environment influence risk.
"How much of the difference we saw is genetic and how much is due to environmental factors that go along with ancestry is not known," Kumar says.
Kids With Food Allergies
About 3 million children in the U.S. have food allergies, according to the American Academy of Allergy, Asthma and Immunology.
An allergy to a specific food is very different from food intolerance, although the symptoms may be similar.
A food allergy occurs when the immune system identifies a component of a particular food as an invader or allergen and produces antibodies to attack it. Severe food allergy reactions can lead to anaphylaxis -- a tightening of the airways leading to shortness of breath, wheezing, swelling -- and even death.
Foods commonly associated with allergies include cow's milk, eggs, fish, peanuts, shellfish, soy, tree nuts, and wheat.
Kumar tells WebMD that little was known about the prevalence of food allergies by race until the publication of a study last fall involving participants in the nationally representative National Health and Nutrition Examination Survey (NHANES).
The study found that African-Americans have a threefold higher risk for food allergies than the general population and that African-American male children had the highest food allergy rates in the U.S., with a fourfold higher risk.
Among people of all races in the U.S., the highest food allergy rates were reported among children under the age of 6 (4%). Adults over the age of 60 had the lowest rates (about 1%).
Food Allergies and Race
In an effort to better understand the reasons for the racial disparity in food allergies, Kumar and colleagues analyzed data on just over 1,100 predominantly minority children enrolled in a Boston-based birth study.
Their analysis included genetic assessment of ancestry because, in the U.S. especially, self-identified race may underestimate genetic variability, especially for African-Americans and Hispanics, Kumar says.
"There is often a great deal of variation even within groups that self-identify as one race," he says.
Genetic ancestry was determined by measuring accepted genetic variations associated with African, European, and Asian descent.
About one in three study participants had evidence of food allergies. Self-reported black race was associated with a more than twofold increase in food allergy risk.
Genetic African ancestry was associated with a high risk of peanut allergy, with each 10% increase in African ancestry increasing the risk by 25%.
Kumar and colleagues hypothesize that environmental factors, such as the timing of a food's introduction, may be the major trigger for milk allergies, while genes may play a bigger role in peanut allergies.
Andrew H. Liu, MD, who led the NHANES-data study, tells WebMD that the new research adds to the evidence that African-Americans have a higher risk for food allergies.
Liu is an associate professor of pediatric allergies at National Jewish Medical Research Center in Denver.
"We still don't know how much of this risk is attributable to African ancestry and genetic heritage and how much is due to other causes," he tells WebMD. "But at the clinical level, this is something we need to be aware of."