July 15, 2008

Stomach Bug May Protect Children From Asthma

U.S. Researchers reported on Tuesday that a type of bacteria only recently revealed as a major cause of ulcers and stomach cancer may help protect children from developing asthma.

Helicobacter pylori, a bacterium that has co-existed with humans for at least 50,000 years, may lead to peptic ulcers and stomach cancer, but children between the ages of 3 and 13 who carried the bug were 59 percent less likely to have asthma than uninfected children, they reported.

"Our findings suggest that absence of H. pylori may be one explanation for the increased risk of childhood asthma," said Yu Chen, assistant professor of epidemiology at New York University School of Medicine, who worked on the study.

"Among teens and children ages 3 to 19 years, carriers of H. pylori were 25 percent less likely to have asthma."

These results are based on an analysis of data gathered from 7,412 participants in the fourth National Health and Nutrition Survey (NHANES IV) conducted from 1999 to 2000 by the National Center for Health Statistics.

The study showed that 5.4 percent of children born in the 1990s tested positive for H. pylori.

"If you look at the people born in 1919, 60 percent are positive. That's a huge change," Blaser. "I have referred to this as global warming of the stomach."

Blaser said during the same time, asthma rates have soared. Among the children aged 3 to 19 in the study, 23 percent had asthma.

Blaser believes the rise in asthma over the past decades could stem from the fact that a stomach harboring H. pylori has a different immunological status from one lacking the bug.

"The disappearance of Helicobacter ... is consistent with the decline of both ulcer disease and stomach cancer. It is also consistent with the rise of asthma and esophageal diseases like GERD (gastric reflux disease) and adenocarcinoma (cancer) of the esophagus."

Blaser said more study was needed on whether Helicobacter infections directly affect a tendency to asthma.

He said it was possible that H. pylori is a marker for something, just as blond hair is a marker for having been born in Scandinavia.

"Maybe the same antibiotics that made H. pylori go away make something else go away."

It is even possible that the bacteria somehow protects against asthma directly, perhaps by changing the body's immune response.

Blaser's team wrote of one explanation for this phenomenon that has been termed the 'hygiene hypothesis,' which considers that humans are more prone to allergic disorders because of a lifestyle that may be too 'clean'.

The presence of the bacteria in the stomach may influence how a child's immune system develops: if a child does not encounter Helicobacter early on, the immune system may not learn how to regulate a response to allergens. Therefore, the child may be more likely to mount the kinds of inflammatory responses that trigger asthma.

The study appears in the July 15, 2008, online issue of The Journal of Infectious Diseases.


Image Caption: Electron micrograph of H. pylori possessing multiple flagella (negative staining). Courtesy Yutaka Tsutsumi, M.D. Professor Department of Pathology Fujita Health University School of Medicine (Wikipedia)


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