Why Black Children May Be More Likely to Develop Food Allergies

9/06/2011 23:48:57 PM

New research suggests that race and ancestry may play an important role in food allergies.

Dr. Rajesh Kumar, a pediatrician at Northwestern University Medical School, and his team report in the journal Pediatrics that black children are more than twice as likely as white children to have sensitivities to eight foods that commonly cause allergic reactions, and that they are especially vulnerable to peanut allergies.

While other studies have linked African American ethnicity to a higher risk of asthma, Kumar's group was interested in investigating whether race also affects children's risk of allergy to certain foods. Using a multi-ethnic database of 1,104 children who participated in regular health checkups at 6 months, then again at 1, 2, 4 and 6 years old, the scientists measured the youngsters' antibodies to egg white, cow's milk, peanut, soy, shrimp, walnut, wheat and cod.

To determine race, the researchers used two measures — the children's mothers' self-report of race as well as the distribution of 150 genetic markers in the children's blood, which track ancestry. The researchers included the second, more objective measure because self-reports of race can often be inaccurate, especially given the amount of racial mixing that occurs in a country as diverse as the U.S.

"If you look at populations who describe themselves as one race like African American or Hispanic, they may have ancestors from different continental groups," says Kumar. "So the description loses precision if you just use race. Whereas if you look at ancestry, you get a more precise proportion of what ancestors came from one continent compared to another."

The researchers found that children whose mothers reported them as being black were nearly 2.5 times as likely as self-reported white youngsters to be sensitive to any of the eight foods tested, and they were also more likely to be sensitive to more of the foods than white children.

When the researchers looked at the genetic markers for ancestry, they found that for every 10% increment in African ancestry, children were 7% more likely to have antibodies to the allergy-causing foods than white children. And the association was strongest for peanuts; more children with African ancestry showed antibody levels that would correlate to a possible allergic reaction if they were to eat peanuts.

Kumar stresses that his findings do not suggest that black children with more African ancestry are likely to develop food allergies, or even a peanut allergy. His study was only able to find links between levels of antibodies that are likely to generate a reaction.

"This is one way for us to start teasing out why there are increased risks in this population," he says. "What we did was confirm that, one, yes, there is increased risk among black children for food sensitization and, two, we are starting to get at why they are at increased risk."

Although the genetic markers are likely to reflect some inherited factors that affect how the immune system reacts to foods, it's also possible that they encompass environmental factors. For example, the children who self-reported themselves as black showed a stronger likelihood of sensitization to milk and egg allergens, but not to peanuts, while those with more African ancestry showed the opposite trend: they were more likely to be sensitive to peanuts but not to milk and egg.

"Overall, black children seem to be at higher risk of being sensitive to foods, but if you break down that risk, self-identifying as black explains the risk to milk and egg allergens but not to peanut, while ancestry explains some of the risk to peanut allergens," says Kumar. "That may mean that different factors go along with an individual's self-identified race compared to their genetic ancestry."

These factors may include things such as the fact that newborns of African American ancestry tend to have lower vitamin D levels, which has been linked to an increased risk of allergic diseases. Or, that those who identify themselves as being black may adhere to cultural dictates for when babies are introduced to milk, which can affect how newborns' immune systems react to it.

Kumar acknowledges that the findings probably won't translate into any useful guidelines for parents or pediatricians quite yet. But they serve as a good foundation for a better understanding of which factors related to race and ancestry might affect how we react to common allergens like those found in foods. "Once we identify the genes or environmental factors specifically responsible for the differences, then we will be in a better position to pinpoint individuals at risk," he says. "This opens the door to that work."

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