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SAN ANTONIO -- Foreign-born children who did not have allergies when they came to the U.S. became more likely to develop them after 10 years of residence, researchers found.
Compared with foreign-born children who had lived in the U.S. for 2 or fewer years, children who lived in the U.S. for over a decade were at three times the risk for developing any allergic disorder (adjusted odds ratio [aOR] 3.04, 95% CI 1.08 to 8.60, P=0.03), particularly eczema (aOR 4.93, 95% CI 1.18 to 20.62, P=0.03) and hay fever (aOR 6.25, 95% CI 1.70 to 22.96, P=0.006), according to Jonathan Silverberg, MD, PhD, of St. Luke's-Roosevelt Hospital Center in New York, N.Y., and colleagues.
Although their risk of developing allergies does increase the longer they stay in the U.S., foreign-born children start out with an advantage when it comes to allergies. So, overall, birthplace outside of the U.S. and having one or more parents born outside of the U.S. offered a protective benefit against most allergic conditions (P<0.0003), they reported at a poster session during the meeting of the American Academy of Allergy, Asthma, and Immunology.
Silverberg noted that allergic disease is much less common in other countries -- such as Mexico and China -- than it is in the U.S., which may be in part due to conditions including socioeconomic status, ethnicity, urban living, nutrition, adiposity, and pollutants.
However, even after adjusting for ethnicity, socioeconomic status, and urban residence, the investigators found that U.S. residence of foreign-born children over long periods of time was "a previously unrecognized factor in the epidemiology of atopic disease."
To study this association, the researchers gathered data from 78,853 participants in the 2007-2008 National Survey of Children's Health on prevalence of allergic disorders. The sample included 1,989 children born outside of the U.S. and 76,864 U.S.-born children.
Researchers asked participants' parents questions on whether their child had been diagnosed with ever or current asthma, eczema or other skin allergies, hay fever, and food allergies. They also assessed place of birth for the mother, father, and child, as well as length of U.S. residency for the child.
Other characteristics included the child's age, sex, and ethnicity, as well as household income, residency in a metropolitan area, and history of moving to a new address.
Among foreign-born participants, children were a mean 11.5 years old and most were Hispanic (53.4%), white (17.2%), or black (12.5%) and lived in a metropolitan area (94.7%).
Children whose parents were born outside of the U.S. were significantly less likely to have an atopic disorder than those whose parents were born in the U.S. overall.
Children born to foreign mothers were significantly less likely to have any allergy overall, asthma, eczema, hay fever (P<0.001 for all), or food allergies (P=0.001). Those born to foreign fathers had protective effects against any allergy overall, ever asthma, eczema, food allergy (P<0.001 for all), current asthma (P=0.009), and hay fever (P=0.01).
Birthplace outside of the U.S. also offered a protective benefit against allergic disease, including against any allergy overall, ever or current asthma, hay fever (P<0.001 for all), or eczema (P=0.003), but there was no significant difference in rates of food allergy (P=0.46).
The longer foreign-born children lived in the U.S., the more likely they were to develop allergies. "The odds of developing allergic disease significantly increased after residing in the U.S. for a decade or more," Silverberg presented, noting the difference between those who had lived in the U.S. for more than 10 years with those who lived there 2 years or less (P=0.03).
"This suggested that foreign-born U.S. residents might be at increased risk for later onset of allergic disease," the authors concluded.
The authors declared no conflicts of interest.
- Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner
American Academy of Allergy, Asthma and ImmunologySource Reference: Silverberg JI, et al "Reduced prevalence of allergic diseases in foreign born American children is reversed after U.S. residence" AAAAI 2013; Abstract 512.