Among children born in the United States, low socioeconomic status (SES) and exposure to pests (mice and cockroaches) were both associated with having asthma. Neither association was present in children born outside of the United States. The study was published online in advance of print in the Journal of Immigrant and Minority Health.
"In earlier studies, we found that country of birth was associated with asthma risk, which led us to the current analyses. Our current findings may help bring a new perspective to asthma research as they highlight the importance of studying foreign-born children. Much of the existing research follows U.S.-born children from birth to see if, and potentially why, they develop asthma. It might add to our understanding of what causes asthma if we knew why foreign-born children seem to be less likely to develop asthma," said Doug Brugge, PhD, MS, senior author and professor of public health and community medicine at Tufts University School of Medicine. Brugge co-authored the five previous studies that were analyzed for this study.
"Pooling data from these studies gave us a larger sample size and allowed us to conduct additional analyses. We found that, in addition to an association with place of birth; both low SES and exposure to pests are associated with asthma in U.S.-born children but not in foreign-born children," said first author Mark Woodin, ScD, MS, senior lecturer in the department of civil and environmental engineering at Tufts University School of Engineering and senior lecturer in the department of public health and community medicine at Tufts University School of Medicine.
"While this type of epidemiological study cannot establish causation, our findings may be explained by the fact that certain pathogens common in the developing world are nearly nonexistent in the U.S. If exposure to such pathogens confers some sort of protection against developing asthma, foreign-born children may be less susceptible than children born in the U.S.," Brugge said.
This idea, called the "hygiene hypothesis," suggests that children born in less-developed countries may have early exposure to intestinal worms, viruses and bacteria that affects immunity and makes them more resistant to asthma than U.S.-born children.
"There are other hypotheses that could also help to explain the differences between the prevalence of asthma of U.S.-born and foreign-born children, including the vitamin D hypothesis which posits that greater sunlight exposure in the country of origin increases vitamin D to levels that are protective against asthma. It could also be that families who immigrate tend to be healthier people," speculated Brugge.
The five studies Brugge and colleagues examined were conducted from 2002 to 2007, sampling a total of 962 children aged 4 to 18 years. There did not initially appear to be a significant relationship between pest exposure and asthma; but when the researchers took birthplace into account, they found that U.S.-born children who were exposed to pests were 60 percent more likely to have asthma than U.S.-born children not exposed to pests. Pest exposure had no statistically significant impact on asthma risk in foreign-born children. Similarly, U.S.-born children with low SES were two times more likely to have asthma than U.S.-born children without low SES, while low SES had no statistically significant effect on asthma risk in foreign-born children.
Additional authors of the paper, to be published in the Journal of Immigrant and Minority Health, are Alice Tin, an undergraduate student at Tufts University at the time the paper was written, Sarah Moy, an undergraduate student at the University of Massachusetts Amherst, and Michele Palella, MD, PhD, formerly a pediatric pulmonologist at Tufts Medical Center and assistant professor of pediatrics at TUSM.
Woodin M, Tin AH, Moy S, Palella M and Brugge D. Journal of Immigrant and Minority Health "Lessons for Primary Prevention of Asthma: Foreign-Born Children Have Less Association of SES and Pests with Asthma Diagnosis." Published online October 16, 2010, doi: 10.1007/s10903-010-9407-8
About Tufts University School of Medicine and the Sackler School of Graduate Biomedical Sciences
Tufts University School of Medicine and the Sackler School of Graduate Biomedical Sciences at Tufts University are international leaders in innovative medical education and advanced research. The School of Medicine and the Sackler School are renowned for excellence in education in general medicine, biomedical sciences, special combined degree programs in business, health management, public health, bioengineering and international relations, as well as basic and clinical research at the cellular and molecular level. Ranked among the top in the nation, the School of Medicine is affiliated with six major teaching hospitals and more than 30 health care facilities. Tufts University School of Medicine and the Sackler School undertake research that is consistently rated among the highest in the nation for its effect on the advancement of medical science.
Tufts University School of Engineering is dedicated to educating the technological leaders of tomorrow. Located on Tufts' Medford/Somerville campus, the School of Engineering offers a rigorous engineering education in an environment characterized by the best blending of a liberal arts college atmosphere with the intellectual and technological resources of a world-class research university. Close collaboration with the School of Arts and Sciences and the university's extraordinary collection of excellent professional schools creates a wealth of educational and research opportunities. The School of Engineering's primary goal is to educate engineers committed to the innovative and ethical application of technology in the solution of societal problems. It also seeks to be a leader among peer institutions in targeted areas of interdisciplinary research and education that impact the well-being and sustainability of society, including bioengineering, sustainability and innovation in engineering education.
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Siobhan E. Gallagher | EurekAlert!
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