April 30, 2013
Foreign-Born US Children Have Less Allergies Than Those Born In America
Lawrence LeBlond for redOrbit.com - Your Universe Online
In a new study of nearly 80,000 children, researchers have found foreign-born US children have significantly fewer allergies than those born in the US. However, this lower allergy risk begins to dissipate after these children have been in America for ten years, according to the study, published in the latest issue of JAMA Pediatrics.
The research team further noted children born outside the US with both parents born abroad had even lower risk of allergies than those with parents born in the US.
Study leader Jonathan Silverberg of St. Luke´s told the AFP by email the study indicates children born outside the US have a one in five chance of developing an allergy when moving to the US, while American born children have a one in three chance.
"However, foreign-born Americans develop increased risk for allergic disease with prolonged residence in the United States," he added, noting a length of residency over 10 years showed “significantly” higher odds of developing some allergies (eczema and hay fever) but not others (asthma and food). He also added results were the same no matter what age they entered the country
According to the study findings, foreign-born children have a five-times higher risk of developing eczema when they are in the country for more than 10 years and a six-time higher chance of developing hay fever over the same time period when compared to foreign-born children who have only lived in the US for two years or less.
Silverberg and his colleagues said this is the first time a study has found the duration someone lives in the US translates to the risk of developing allergic diseases. They suggest acculturation and parental behavior while in the US could be a driving factor for the risk.
According to the researchers, nearly 8.9 percent of US children have asthma and 10.6 percent have eczema. In countries like Mexico and China, this rate is much lower. The team believes different environmental factors and childhood infections may be significant contributors to the “hygiene hypothesis.”
Brian Krans of Healthline explains the hygiene hypothesis as follows: “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.”
Silverberg and his colleagues said their study results are consistent with the hygiene hypothesis, but as the risk of developing allergies increase after foreign-born children have lived in the US for longer than ten years, protection rates drop.
“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,” said the researchers.
Previous research has shown children who grow up in developing nations tend to have lower risk of allergies. Experts believe the reasoning behind this is these people are exposed to many more infections, bacteria and disease that allow them the ability to build up better immune systems.
The study team said more research is needed to find out if allergies increase for immigrants in other countries after they have lived there for long periods of time, as researchers have found some countries have similar allergen risks to the US.