Already known for their higher-than-usual risk of asthma and environmental allergies, young inner-city children appear to suffer disproportionately from food allergies as well, according to results of a study led by scientists at the Johns Hopkins Children's Center.
The federally funded 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. However, the true number may be even higher, the investigators say, because the study used highly stringent criteria and counted only the three most common food allergies.
Nearly 3 percent of adults and 6 percent of young children in the United States have one or more food allergies, according to the latest estimates from the National Institutes of Health. Moreover, Wood notes, food allergies among children have been on a steady rise over the last 20 years, and experts have long suspected that children in urban areas are no exception. 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 investigative team followed 516 inner-city children from birth through age 5, living in Baltimore, Boston, New York City and St. Louis. 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.
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 IgE antibodies but no clear history of allergic reactions to peanuts, eggs or milk. Twenty-nine percent were classified as "sensitive but tolerant," a group that included those with elevated IgE antibodies and a known history of consuming allergenic foods but who were able to tolerate the foods in question without allergic symptoms.
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.
The study was funded by National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, under grant numbers NO1-AI-25496, NO1-AI-25482, HHSN272200900052C and HHSN272201000052I. Additional support was provided by the National Center for Research Resources under grants, RR00052, M01RR00533, 1UL1RR025771, M01RR00071, 1UL1RR024156, and 5UL1RR024992-02.
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Journal of Allergy and Clinical Immunology