H pylori has co-existed with humans for at least 50,000 years. About a quarter of the population may have it at some point in their lives; most have no symptoms, but in a small percentage it can lead to peptic ulcers and stomach cancer.
Asthma is a serious worldwide health problem and is still rising. In the meantime, H pylori, which was once universal in humans, is gradually disappearing in developed countries where more people use antibiotics, have cleaner water and cleaner homes.
Using data from the National Health and Nutrition Examination
Survey (NHANES ) 1999–2000, Dr Yu Chen of the New York University School of Medicine, and Dr Martin J Blaser, professor of internal medicine NYU Langone Medical Center found that only 5.4% of children born in the 1990s tested positive for H pylori. Among teens and children aged 3 to 19 years, carriers of H pylori were 25% less likely to have asthma. The findings suggest that absence of H pylori may be one explanation for the increased risk of childhood asthma.
Speculating on the findings, Dr Blaser suggested that the rise in asthma could result from the fact that a stomach colonised by H pylori has a different type of immune status from one that lacks the bug. When the bacterium is present, the stomach lining contains a greater population of regulatory T-cells that are setting a higher threshold for sensitisation.
For example, if a child doesn't have helicobacter and has contact with two or three cockroaches, he may get sensitised to them. But if helicobacter is directing the immune response, even if a child comes into contact with many cockroaches he may not get sensitised because his immune system is more tolerant.
H pylori influences the development of a child's immune system. If the child does not meet it early in life, then the immune system may not ‘learn’ how to respond effectively to allergens, making it more likely that it will mount the kind of inflammatory response that triggers asthma and other reactions.
Helicobacter is disappearing extremely rapidly. In the NHANES study, less than 6% of US children had helicobacter whereas two generations ago it was 70%.
The paper was published in the July 2008 online issue of the The Journal of Infectious Diseases.
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