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Are pesticides and food allergies linked?

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People who are exposed to higher amounts of chemicals used to chlorinate water and kill crop pests are also more likely to suffer from food allergies.

The new finding doesn't prove or even suggest that pesticides or water chlorination cause food allergies. But it's possible that a class of chemicals called dichlorophenols could alter the population of microbes in the human body, in turn influencing the immune system's reaction to food triggers.

"Both environmental pollution and the prevalence of food allergies are increasing in the United States," said lead author Elina Jerschow, a practicing allergist in New York City. "The results of this study suggest that these two phenomena might be linked."

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In the United States, food allergies affect between 1 and 3 percent of adults and between six and eight percent of children, said Dr. Clifford Bassett, an allergist in New York City and spokesperson for the American College of Allergy, Asthma and Immunology. And bad reactions to foods have grown more common in recent years, with as much as a 20 percent increase in kids in the last decade.

In an attempt to help explain those trends, Jerschow and colleagues turned to dichlorophenols, which get into our bodies when we drink chlorinated water, come into contact with pesticides that contain them or breathe contaminated air.

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Dichlorophenols are designed to kill microbes, making them a possible player in support of the hygiene hypothesis. The theory proposes that keeping our environments too clean can backfire, causing the immune system to over-react to potential allergens. In other words, exposure to dirt and germs may help reduce the risks of allergies, especially for young children. Anything that kills germs, then, might have the potential to raise allergy risks.

Using data collected by the U.S. National Health and Nutrition Examination Survey (NHANES) in 2005 and 2006, the researchers looked at concentrations of a variety of dichlorophenols in the urine of more than 2,200 people, ages 6 and older. They also looked at blood-test results indicating allergies to peanuts, eggs, milk or shrimp.

People with the highest levels of dichlorophenols were 80 percent more likely to have food allergies compared to people with the lowest levels, the researchers reported today in the journal Annals of Allergy, Asthma and Immunology.

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It's far too soon to conclude that pesticides or chlorinated water cause or increase the risk of allergies. Instead, Bassett said, the new study offers an intriguing new line of study that's worth pursuing.

"It's not a slam dunk or proof of cause and effect, but it's an area of research that's very thought-provoking and it's not clear how it will pan out," Bassett said. "We're all kind of scratching our heads to interpret this so we can make the right recommendations to our patients."