Children born outside of the United States have lower allergy rates than US-born children. But now researchers have found that foreign-born children's allergy risk changes the longer they live in the US.
These researchers looked at where children were born, how long they’d lived in the US and if they developed any allergies.
Children born outside of the US had a lower risk of developing allergies than US-born kids, but their allergy rates increased the longer they lived in the US.
Jonathan I. Silverberg, MD, of St. Luke’s-Roosevelt Hospital Center in New York, and colleagues wanted to find out when and how often children born outside of the US developed allergies after moving to the US.
For their study, the researchers used data from 91,642 children enrolled in the 2007–2008 National Survey of Children’s Health. The children in the survey were between the ages of 0 and 17 years old.
The researchers looked through the records to find place and date of birth, date of arrival to US if foreign-born and whether or not the children had allergies. Specifically, they looked for asthma, eczema, hay fever and food allergies.
The analysis showed that children born outside of the US had significantly lower rates of allergic disease.
Children born outside of the US had 0.48 times the odds of developing allergies in general compared to US-born children. They had similarly lower odds of developing specific allergies to a variety of substances.
Foreign-born children had 0.53 times the odds of ever having developed asthma and 0.34 times the odds for having current, active asthma when compared to children born in the US.
Foreign-born children had 0.43 times the odds of experiencing eczema, 0.39 times the odds of having hay fever and 0.60 times the odds of developing food allergy compared to American-born children.
Children born outside of the US whose parents were also foreign-born had even lower chances of developing an allergic disease than US-born children.
The researchers also found that foreign-born children who lived in the US for more than 10 years had 3.04 times higher odds for developing some type of allergies than foreign-born children who lived in the US for two years or less.
The children that had lived longer in the US had 4.93 times higher odds of developing eczema and 6.25 times higher odds of hay fever than the children with shorter stays.
The foreign-born children who had been in the US for more than 10 years did not have higher rates of asthma or food allergy.
“What we can take away here is that seeing this loss of childhood protection from eczema and hay fever after extended US residence implies that environmental factors may promote the development of allergic disease,” said Dr. Silverberg.
The study was presented at the American Academy of Allergy, Asthma and Immunology annual meeting in San Antonio, Texas on February 24. The study has yet to be published in a peer-reviewed journal, so the results are still preliminary.
It was published as an abstract in a supplement of the February issue of The Journal of Allergy and Clinical Immunology.