Foreign-born U.S. children have lower odds of developing allergic diseases like asthma and food allergies than children born in the U.S., according to .
However, researchers from St. Luke’s-Roosevelt Hospital Center in New York City say that the allergy protection dissipates after a decade of living in the U.S. They assessed the health of almost 80,000 children in the 2007-2008 .
The study, released today in the journal , also states that children born outside the U.S. with both parents born abroad had even significantly lower odds than those with parents born in the U.S.
“In conclusion, foreign-born Americans have significantly lower risk of allergic disease than US-born Americans. However, foreign-born Americans develop increased risk for allergic disease with prolonged residence in the United States,” the .
Researchers say the study shows that the duration someone lives in the U.S. is a previously unrecognized factor in the development of allergic diseases, such as asthma, eczema, food allergies, hay fever, and other allergies. Acculturation and parental behavior while in the U.S. could be contributing factors to this risk, researchers said.
The study’s lead author, dermatologist Jonathan Silverberg, could not be reached for comment Monday.
Allergies in America and the ‘Hygiene Hypothesis’
Researchers said, based off their previous research, that certain infections and exposures at a young age can help guide a person’s immune system away from a “pro-allergic” state and decrease one’s risk for asthma and allergic eczema.
The St. Luke’s study says that different environmental factors and childhood infections may contribute to the “hygiene hypothesis.”
The basis of the hygiene hypothesis is that a child’s immune system never fully develops because of the lack of exposure to germs and microorganisms in childhood, increasing a person’s likelihood of allergies namely in developed countries. While there is mounting evidence supporting the hypothesis, scientists have yet to determine a cause-and-effect relationship.
Previous research, including a study published in the journal , offers evidence that the decline in childhood infections in the industrialized world could explain the rise of allergic diseases.
The St. Luke’s study states their findings are consistent with the hygiene hypothesis, but as the odds of developing allergies dramatically increase after foreign-born children have lived in the U.S. for more than a decade, the protection may not be life-long. Researchers hypothesize that exposure to allergens and other environmental factors in the U.S. may trigger allergic diseases later in life.
“In the present study, age at the time of immigration was not a significant predictor of allergic disease and did not significantly modify the effects of duration of US residence,” the study concludes.