More than 3 million Americans now have some kind of nut allergy, with cases of peanut allergy in children more than tripling between 1997 and 2008, according to a report released this week.
"These results show that there is an alarming increase in peanut allergies, consistent with a general, although less dramatic, rise in food allergies among children in studies reported by the [Centers for Disease Control and Prevention]," said lead researcher Dr. Scott Sicherer, professor of pediatrics at the Jaffe Food Allergy Institute at Mount Sinai School of Medicine. "The data underscore the need for more study of these dangerous allergies."
Sicherer and colleagues surveyed 5,300 households, representing 13,534 individuals in 2008, and compared the numbers with those from the same survey conducted in 1997 and 2002.
In 2008, 1.4 percent of children in the survey were reported to have peanut allergies, compared with just 0.4 percent in 1997. The prevalence of combined peanut or tree nut allergies in children was 2.1 percent in 2008, compared with 0.6 percent in 1997.
The study results, which are published in the May 12 issue of the Journal of Allergy and Clinical Immunology, have their limitations. Telephone surveys that immediately exclude those without telephones could bias the results toward households of high socioeconomic status, the researchers say. And self-reports can be unreliable, though the numbers estimated are similar to those found in research using different methods in Canada, Australia and the U.K.
In addition, the prevalence of food allergies is difficult to pin down, with a recent review of research in the field showing food allergies affect more than 1 to 2 percent of the population and no more than 10 percent. The uncertainty is due to a lack of uniform criteria for diagnosing food allergies, according to the report published this week in the Journal of the American Medical Association.
Why allergies are on the rise
No one is certain what's behind the spike in food allergies.
In general, those with food allergies have extra-sensitive immune systems that react to harmless substances called allergens found in certain foods and drinks. When the person eats a peanut or other allergic item, the body produces antibodies to the specific allergen, leading to an immune reaction. Essentially, the body tries to get rid of the allergens.
One idea for the cause called the hygiene hypothesis posits we're too clean. Squeaky-clean living and the use of medications to prevent and quickly treat infections leaves the immune system under-stimulated. This "bored" immune system then goes and attacks harmless proteins like those in foods, pollens and animal dander.
Other theories include the timing of introduction of the food and how the food is prepared.
Predicting allergy early
Even without this knowledge, scientists are learning more about how to predict peanut allergy. Another recent study of more than 500 infants with egg or milk allergy suggests these infants are at risk for developing peanut allergy later in life and should be seen by a doctor before introducing peanuts into their diet, the researchers say. The study is also detailed this month in the Journal of Allergy and Clinical Immunology.
When the infants were enrolled, at 5 months to 15 months of age, none were known to have a peanut allergy. The researchers found that more of the infants had elevated levels of the so-called IgE antibody to peanuts than anticipated. Some of these infants showed such high antibody levels, the researchers say they may already be allergic to peanuts without their parents knowing it.
Scientists have known infants with a milk or egg allergy are at risk for developing a peanut allergy later in life. But this is the first study of the natural development of the three food allergies in very young children. (Another non-food risk factor is the skin problem eczema.)
The infants will be followed until they are age 5 so researchers can see if the allergy to milk or eggs continues or resolves, and whether the children develop an allergy to peanuts.
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