Young inner-city children, who are already known to have a higher-than-usual risk of asthma and environmental allergies, also appear to suffer disproportionately from food allergies, according to results of a study led by scientists at the Johns Hopkins Children's Center.
The multi-center study, described online Aug. 13 in the Journal of Allergy and Clinical Immunology, found that at least one in 10 children from four large U.S. cities has a food allergy. The true number may be even higher, researchers say, because the study used highly stringent criteria and counted only the three most common food allergies—milk, eggs, or peanuts
"Our findings are a wake-up call, signaling an urgent need to unravel the causes, contributors, and mechanisms that drive the high prevalence of food allergies among an already vulnerable group known for its high risk of asthma and environmental allergies," says senior investigator Robert Wood, director of pediatric allergy and immunology at Johns Hopkins.
Nearly 3 percent of adults and 6 percent of young children in the United States have one or more food allergies, according to the most recent estimates from the National Institutes of Health. Wood notes that food allergies among children have been on a steady rise over the past 20 years, and the new study largely affirms that trend but also points to a subgroup of children who may have higher-than-average allergy risk.
For the study, the researchers followed 516 inner-city children living in Baltimore, Boston, New York City, or St. Louis from birth through age 5. Each year of the study, the investigators measured each child's exposure to household allergens, conducted physical exams, tracked the children's diets and reviewed their health histories. The team also analyzed blood samples at 1, 2, 3 and 5 years of age to measure the presence of food-specific antibodies—immune chemicals released by the body that indicate a food allergy—to milk, eggs, and peanuts.
Overall, more than half (55 percent) of children in the study were classified as sensitive to milk, eggs, or peanuts. Nearly 10 percent of them met criteria for a full-blown food allergy. The most common allergy was to peanuts (6 percent), followed by eggs (4.3 percent), and milk (2.7 percent). An additional 17 percent were classified as "possibly allergic," a subgroup that had elevated antibodies but no clear history of allergic reactions.
Breastfed children appeared to have a higher risk for developing food allergies. Children living in houses with higher levels of endotoxin, a molecule released by certain types of bacteria, were less likely to have a food allergy. This latter finding, the investigators say, is consistent with the so-called hygiene hypothesis, which suggests that early-life exposure to certain microbes can play a protective role against asthma and allergies.
Children with food allergies were also more likely to suffer from environmental allergies, wheezing, and eczema, an allergic skin condition.
Other institutions involved in the research included Boston University School of Medicine, the Washington University School of Medicine in St. Louis, Columbia University Medical Center in New York, and the University of Wisconsin School of Medicine and Public Health.
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