The number of kids with food allergies is rising, the study finds, but the reason is unclear. According to the lead author, the increase goes beyond a rise in awareness.
The number of children who have food allergies is not only increasing, it now encompasses 4 per cent of all kids in the United States, according to an analysis of four large, national surveys published Monday in the journal Paediatrics.
The study – the first to make a broad estimate about the prevalence of food allergies among US children – supports previous studies suggesting that allergy rates are rising rapidly, for reasons that are unclear.
Government researchers found that self-reported food allergies increased 18 per cent between 1997 and 2007. Healthcare visits for food allergies in children nearly tripled between two time periods studied: 1992 through 1997 and 2003 through 2006. In the later period, US children had an average of 317,000 visits to healthcare settings per year for food allergies.
The data suggest a real surge in illnesses and not just better awareness and diagnosis, said the study’s lead author, Amy M. Branum, a statistician with the National Centre for Health Statistics.
“To see almost a tripling of visits in a 13-year period is pretty good evidence that this isn’t just parents hearing about food allergies on the news and then thinking their children have it,” Ms Branum said. “We used four different surveys, and to see an increase in food allergies in all of those surveys is very telling.”
Most of the data were drawn from surveys of children’s parents. However, using medical records from 2005-06, researchers also found that 9 per cent of children in one survey tested positive for IgE antibodies to peanuts. IgE antibodies are found in the lungs, skin and mucous membranes, usually in response to food allergies.
The study also suggests potential racial differences among children with food allergies. Although Latino children had the lowest prevalence of food allergies in 2007 compared with other racial groups, they had the greatest increase in reported food allergies over the period studied.
“It’s very possible that what we’re seeing with Hispanic children is more awareness of food allergies,” Ms Branum said.
The IgE antibody tests also showed ethnic variation. For example, black children were nearly twice as likely as white children to have antibodies to peanuts, twice as likely to have antibodies to milk and four times as likely to have antibodies to shellfish.
Several theories have been proposed to explain why more children have food allergies, Branum said.
A prominent theory is the hygiene hypothesis, which is based on the notion that today’s children are less exposed to germs and other disease-causing substances than were previous generations – preventing their immune systems from developing the same responses to protect against invaders. The immune system then overreacts to relatively harmless substances, causing allergies, eczema or asthma.