A recent article in JAMA Pediatrics has some interesting conclusions regarding allergies and asthma prevalence in U. S. children that were born outside the United States. The team led by Dr. Jonathan Silverberg of St. Luke’s – Roosevelt Hospital Center, New York found that these children had significantly lower odds of any atopic disorders than those born in the United States. Children born outside of the United States whose parents were also born outside of the United States had significantly lower odds of any atopic disorders than those whose parents were born in the United States. Children born outside the United States who lived in the United States for longer than 10 years when compared to those who resided in the U.S. for only 0 to 2 years had significantly higher odds of developing any allergic disorders, including eczema and hay fever, but not asthma or food allegies. The children in this group had similar levels of allergy and asthma to children who were born in the U.S..
The press release on this article has brought out some interesting hypotheses on why there might be higher rates of allergies and asthma in children born inside the United States. Most of the articles claim that this is confirmation of the “hygiene hypothesis” and that the too clean U. S. environment is adding to the allergy and asthma numbers. Other reporters have said that this article is proof that the pollution in the U. S. is the culprit and that the rise is numbers is directly related to the rise in air pollution in U. S. cities. Still others have claimed that this article is proof that the diet of Americans is the cause. Too much fast food and genetically modified foods in the U.S. are the reason for this higher level of allergies and asthma of U.S. children born in the United States. Then there is the lack of exercise argument. It seems like every pet theory is supported by this study – or is it?
There might be another cause – better information about allergies and asthma in the United States. The study is actually based on a survey of 90,000+ children and parents of children. Therefore, the prevalence of allergies and asthma is self-diagnosed and reported. It is not based on a clinical analysis of the participants to measure allergic reactions or asthma symptoms. Information about allergies and asthma is better in the U.S. so the perception of allergy and asthma problems is higher. This would also explain the fact that the children born outside the U.S. who stayed in the U.S. longer had the same reported levels of allergy and asthma as those who were born in the U.S..
When you think about it, the better information theory is very plausible. Those who say that the study supports the hygiene hypothesis would have to have the position that the early exposure to germs only gives temporary relief from allergic diseases and that given enough time in the United States all people are equally susceptible. Exposing young children to germs really would not make a difference because according to this study all people wind up the same anyway.
This reminds me of a similar “trend” in the 1990’s in the reported levels of allergies and asthma. In the early 1990’s most experts were of the opinion that somewhere between 15-20% of Americans had allergies. By the end of the 1990’s the percentage had risen to over 30%. Asthma levels had a similar percentage rise. Did something happen in the U. S. environment during this time that caused this massive spike? According to many asthma and allergy specialists I talked to, the rise was most likely due to increased awareness of allergies and asthma among the public and changes in the diagnosis of patients from the medical community. If you look at the numbers, these percentages are not too much different from those reported in the surveys summarized in the study of children born outside the U.S..
The moral of the story here is that we need to be very careful in looking at reported data. Where does it come from? Is it based on perceptions or tests with human subjects? Does the data really support our hypothesis or are we putting a spin on it that makes it support our pre-conceived conclusion? And why DO we have higher levels of allergy and asthma in the U.S.? Is it our too clean environment, our pollution, our bad food, our lack of exercise or just better information. I am going with better information – but that is just my opinion – and opinions are all that we can derive from this study.