US-born children more likely to develop asthma than foreign-born children.

Researchers from Tufts University pooled data from five previous epidemiological studies to investigate the prevalence of asthma in children in the Boston neighbuorhoods of Chinatown and Dorchester.

Much of the existing research follows US-born children from birth to see if, and potentially why, they develop asthma. In this study information was included on foreign-born children who appear to be less likely to develop the condition. Among children born in the US, but not in children born outside the US, low socioeconomic status and exposure to pests (mice and cockroaches) were both associated with having asthma.

This type of epidemiological study cannot establish causation, but its findings may be explained by the fact that certain pathogens common in the developing world are nearly nonexistent in the US. 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 US. This ‘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 US-born children.

An alternative hypothesis suggests greater sunlight exposure in the country of origin increases vitamin D to levels that are protective against asthma.

The five studies 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 US-born children who were exposed to pests were 60% more likely to have asthma than US-born children not exposed to pests whereas pest exposure had no statistically significant impact on asthma risk in foreign-born children. Similarly, US-born children with low socioeconomic status were twice as likely to have asthma than US-born children without low socioeconomic status, while their socio economic status had no statistically significant effect on asthma risk in foreign-born children.


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,


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First Published in October 2010

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