With children's food allergies becoming something of an epidemic in recent years, researchers at Johns Hopkins University wanted to see if the antibodies associated with food allergies have also been rising.
To their surprise, they found no increases in these antibodies in blood samples collected from the 1980s through the 2000s.
Their findings, published this month in the Journal of Allergy and Clinical Immunology, suggest that other factors are to blame for the trend, whether that's simply an increased awareness of food allergies or possibly a changing relationship between the antibodies and food allergy symptoms.
Research has shown that the prevalence of food allergies in children has spiked by at least 50 percent since 1990s, according to senior study author Corrine Keet, a professor of pediatrics at the Johns Hopkins School of Medicine. Today about 5 percent of children in the U.S. have food allergies, most commonly with milk, eggs, shellfish, and peanuts.
"Why allergies have seemed to increase, however, has been unclear," Keet says.
The Hopkins team examined whether the rates of food-specific immunoglobulin E (IgE)—antibodies that are found in the blood of people who suffer allergic reactions to particular foods—were matching the increase in reported allergies. Analyzing blood samples from 8,000 children from ages 6 to 19, the researchers found no increase in the number of children with antibodies to peanut, milk, or eggs, while the numbers with antibodies to shrimp actually decreased.
"We were really very surprised," Keet says.
One possible explanation, she says, is that patients and physicians are simply more aware of food allergies today than they were a few decades ago.
"In the past, there may have been more people who just didn't eat a food because it made them feel sick, but they didn't necessarily call that an allergy," Keet says. "Today, we may be much more likely to suspect allergy when a child has a rash or other symptoms after eating a certain food."
Alternatively, the results "raise the question of whether something has changed in the relationship between food-specific IgE and clinical food allergy over the past few decades," says study author Emily McGowan.
Although food-specific IgE antibodies are essential for the kind of food allergy that leads to an acute reaction, many people with the antibodies can also eat those foods without problems. McGowan pointed to a recent study that showed that introducing peanuts during early infancy prevented most peanut allergies—yet didn't correspond with decreased rates of IgE antibodies to peanuts.
"We don't really understand all of the reasons why one person with IgE to a food will have serious reactions to the food, while another can eat it without problems," McGowan says.
The teams says that further research is needed to learn more about the link between food-specific IgE levels and food allergies.
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