The latest study found that inner-city kids have higher rates of allergies to milk, peanuts and eggs.
Previous studies have shown that children who live in urban environments are more prone to asthma and environmental allergies. And a recent study from the University of Colorado Boulder suggested reduced exposure to rural microbes increases asthma and allergy risk.
According to the National Institutes of Health, around 3% of adults and 6% of young children in the US have at least one food allergy, but Dr. Robert Wood, senior investigator on the latest study from Johns Hopkins, notes that child food allergies have been rising over the last 20 years.
Their research confirms this increase, but the team says it also identifies a subgroup of children who may have an allergy risk higher than the average.
They found that 1 in 10 children in Baltimore, MD, Boston, MA, New York, NY, and St. Louis, MO, have a food allergy, but they note that the actual number could be even higher because the study only counted the three most common allergies.
By comparison, according to Food Allergy Research & Education (FARE), the average for children's food allergies across the US is 1 in 13.
"Our findings are a wake-up call," says Dr. Wood, "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."
Over half of the children were sensitive to the allergens
To conduct their study, the researchers followed 516 inner-city children in the four major cities listed above from when they were born through 5 years of age. During each year, the team measured each child's exposure to allergens in the household and tracked their diets and health histories.
Fast facts about child food allergies in the US
- In 2007, 3 million children under 18 years had a reported food or digestive allergy in the preceding 12 months
- Children with food allergy are 2-4 times more likely to have asthma and other allergies than children without
- Between 2004-06, there were around 9,500 hospital discharges per year relating to food allergies among children.
Additionally, the researchers assessed blood samples of the children throughout the study to measure food-specific immunoglobulin E (IgE) antibodies to milk, eggs and peanuts. They explain that IgE antibodies are immune chemicals released by the body that are an indication of a food allergy.
From this information, as well as other findings and symptoms, the team classified each child as either: allergic, possibly allergic, sensitive to a certain substance or not sensitive.
Results showed that 55% of the children were sensitive to milk, eggs or peanuts, and nearly 10% of them met the criteria for a "full-blown food allergy."
Of the allergens, peanuts were the largest culprit, with 6% of the children being allergic to them. Eggs followed, at 4.3%, and 2.7% were allergic to milk.
Additionally, a further 17% met the criteria for "possibly allergic," which included elevated IgE antibodies but no history of allergic reactions to peanuts, eggs or milk.
A total of 29% were classified as "sensitive but tolerant," which means they had elevated IgE antibodies and a history of consuming allergenic foods but were able to tolerate the foods without any symptoms.
Children with allergies to these foods 'likely underestimated'
When IgE antibodies are present in the blood, it signals that a person is more likely to develop allergic symptoms, but the researchers say it is not enough to diagnose a true food allergy. As such, for their research, the team only identified children as allergic if they had elevated IgE antibodies paired with clinical symptoms.
But because of this strict criterion, Dr. Wood says they have likely underestimated the true number of kids with food allergies in their study.
Children who lived in houses with higher levels of endotoxin - a molecule released by certain types of bacteria - were less likely to have a food allergy, which the researchers say falls in line with the "hygiene hypothesis," a theory that exposure to certain microbes in early life can protect against asthma and allergies.
A previous study led by Dr. Wood focused on how exposure to irritants during the first year of life decreases risks of developing allergies, wheezing and asthma.
In this latest study, he and his team observed that breastfed children appeared to have a higher risk for developing food allergies, which can also make them more likely to experience environmental allergies, wheezing and eczema.
They conclude their study by writing:
"Even given that this was designed to be a high-risk cohort, the cumulative incidence of FA [food allergy] is extremely high, especially considering the strict definition of FA that was applied and that only three common allergens were included."