The number of children with peanut allergies in one Midwestern county has tripled in the past decade, according to a new study that adds to evidence that nut allergies are becoming more common in the developed world.
Researchers reviewed the medical records of several hundred children in Olmsted County, in southeastern Minnesota, and found that new diagnoses of peanut allergy per 10 000 kids rose from two in 1999 to nearly seven in 2007.
Overall, 65 of every 10 000 children in the county - home to a sophisticated countywide electronic health records system - had a verified peanut allergy in 2007.
Nut allergies growing
Though exact percentages of kids with peanut allergies may vary from place to place and study to study, Dr Ruchi Gupta, an associate professor of paediatrics at Northwestern University's Feinberg School of Medicine in Chicago, who was not involved in the research, said, "What's consistent with this article is it does look like peanut allergies, especially among the younger children, are increasing over time."
Dr Maria Rinaldi, lead author of the new report and an epidemiologist at the University of Minnesota in Minneapolis, said estimates of peanut allergy vary because of the way peanut allergy is defined for the purposes of research studies.
Some rely on parents' reports of allergy, which may or may not be validated by a doctor.
Dr Rinaldi and her colleagues took a conservative approach, gathering data from the medical records of more than 500 Olmsted County children with suspected peanut allergies between 1999 and 2007.
The researchers, who published their findings in The Journal of Allergy and Clinical Immunology, only included children who had laboratory-confirmed peanut allergy, narrowing the group down to 171 kids.
They found that fewer children had been diagnosed with peanut allergy in 1999 compared to later years. For instance, just 10 children in the county were diagnosed in 1999, and 30 were diagnosed in 2007.
"No matter how we're defining peanut allergy, we're seeing this consistent increase," said Dr Rinaldi.
Over three quarters of new diagnoses were in children under two years old, and about 70% were boys.
There's no clear explanation for the findings. "The leading theory is about hygiene - with less infection thanks to city living, smaller families, vaccines, sanitation, antibiotics, etc., the immune system is less 'busy' with germs and may become more prone to attack harmless food proteins," said Dr Scott Sicherer, a paediatrics professor at Mount Sinai School of Medicine in New York, in an email.
Dr Sicherer said another theory is that kids receive less vitamin D from sunlight because they are indoors or use sunscreen, and that could alter their immune system responses.
But these remain theories, and no one has proven why allergies are increasing. Because peanut reactions can be severe, even lethal, measures to protect allergy sufferers from accidental exposure are becoming more common too, with peanut bans on airplanes, peanut-free sections of baseball stadiums and "school safe" packaged snacks manufactured in nut-free environments.
(Reuters Health, September 2012)