WebMD Health News
Reviewed By Louise Chang, MD
Sept. 28, 2007 -- More than half of asthma cases in the U.S. are linked to allergies, with sensitivity to cats responsible for 29% of allergy-related asthmas, according to new research from the National Institutes of Health.
Allergic sensitivity to cats, confirmed through skin testing, was associated with a threefold increase in asthma risk in the study, conducted using data from the nationally representative health survey, NHANES III.
Cat allergy was the strongest single predictor of asthma risk among the common allergen exposures examined, but sensitivity to white oak and the common outdoor fungus Alternaria were also independently associated with asthma risk.
"This study confirms that the environment plays a major role in the development of asthma," says Darryl C. Zeldin, MD, of the National Institute of Environmental Health Sciences (NIEHS).
Asthma, Allergies, and Cats
Along with researchers from the National Institute of Allergy and Infectious Diseases (NIAID), Zeldin and NIEHS colleagues examined skin test data for 10 common allergens from a nationally representative sample of 10,508 people between the ages of 6 and 59.
The findings led the researchers to conclude that 56.3% of the asthma cases in the U.S. are linked to allergies.
Each of the 10 allergens was initially found to be associated with an increase in asthma risk, but after adjusting for other potential risk factors only sensitivity to cats (29%), Alternaria (21%), and white oak (21%) remained independent predictors of risk.
Other allergens tested included ragweed, dust mites, Russian thistle, Bermuda grass, peanuts, perennial rye, and German cockroach.
While the study confirms an increase in asthma risk among people with established cat allergies, it says little about the impact of specific exposures to cats or the other asthma-related allergens identified.
The distinction is likely to be important to anyone who shares a home with a feline.
The findings would seem to indicate that exposure to cats increases asthma risk, but other studies have suggested that exposure early in life may actually protect children from developing cat allergies in the first place.
Not All Asthma Cases Linked to Allergies
Zeldin tells WebMD that an as yet unpublished analysis of more recent NHANES data should provide a better picture of exposure-associated risk.
"We are not telling people to get rid of their cats," Zeldin says. "What we can say from this study is that people with documented cat allergies have an increased risk for developing asthma."
He adds that people with such allergies should probably limit their exposure to cats.
"That just makes sense," he says.
The new research also makes it clear that while a large number of asthma cases in the U.S. are associated with allergies, many others -- roughly 45% -- are not.
"This study tells us that allergy is a major factor in asthma," Peter Gergen, MD, MPH, of the NIAID says in a news release. "But this study also tells us that there are many people who get asthma who don't have allergies. We need to do more research to understand what is causing asthma that is not related to allergies."
The study appears in the Sept. 27 online edition of the Journal of Allergy and Clinical Immunology.
SOURCES: Arbes, S.J. Journal of Allergy and Clinical Immunology, Sept. 27, 2007, online edition. Darryl C. Zeldin, MD, senior investigator, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, N.C. Peter J. Gergen, MD, MPH, Division of Allergy, Immunology, and Transplantation, NIAID, NIH, Bethesda, Md.
© 2007 WebMD Inc. All rights reserved.