Researchers in the US have found that childhood asthma is significantly less likely in children infected with Helicobacter pylori (H. pylori), a bacterium that has inhabited the stomach and small intestine of humans for thousands of years. They found that children between the ages of 3 and 13 were nearly 59 per cent less likely to have asthma if they carried the bug.
The study was the work of Dr Yu Chen, assistant professor of epidemiology at New York University (NYU) School of Medicine, and Dr Martin J Blaser, the Frederick H King Professor of Internal Medicine, chair of the department of medicine, and professor of microbiology at NYU Langone Medical Center. The paper is published in the July 2008 online issue of the The Journal of Infectious Diseases.
H. pylori has co-existed with humans for at least 50,000 years, and while about one 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.
“Our findings suggest that absence of H. pylori may be one explanation for the increased risk of childhood asthma,” said Chen.
“Among teens and children ages 3 to 19 years, carriers of H. pylori were 25 percent less likely to have asthma,” he added.
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, Chen and Blaser found that only 5.4 per cent of children born in the 1990s tested positive for H. pylori, and 11.3 per cent of the children under 10 had received an antibiotic in the previous month.
Chen and Blaser used data from 7,412 people in the NHNES survey and looked for links between H. pylori and childhood asthma.
The results showed that:
- There was an inverse link between presence of H. pylori and onset of asthma before the age of 5 and current asthma in children aged 3 to 13.
- Among those aged 3 to 19, the presence of H. pylori was inversely linked to ever having had asthma.
- Also in this age group, the link between H. pylori presence and onset of asthma before the age of 5 was stronger.
- Among the 3 to 13 year olds, H. pylori was significantly inversely linked to current asthma.
- Also in this age group, H. pylori was inversely related to recent wheezing, allergic rhinitis, and dermatitis, eczema, or rash.
Chen and Blaser concluded that:
“This study is the first to report an inverse association between H. pylori seropositivity and asthma in children.”
They said the finding calls for new directions in research and asthma prevention.
Speculating on their findings, Blaser suggested that the rise in asthma over the past decades could be the result that a stomach colonized 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 regulatory T cells, immune cells that control response to invaders. Without these cell, the child can be more vulnerable to allergens.
Blaser said their theory was that:
“If you have Helicobacter you have a greater population of regulatory T-cells that are setting a higher threshold for sensitization.”
“For example, if a child doesn’t have Helicobacter and has contact with two or three cockroaches, he may get sensitized to them. But if Helicobacter is directing the immune response, then even if a child comes into contact with many cockroaches he may not get sensitized because his immune system is more tolerant,” explained Blaser.
So Chen and Blaser suggest that 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 doesn’t “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.
Blaser said there is growing evidence that using antibiotics early in life increases asthma risk, “and parents and doctors are using antibiotics like water”.
“The reality is that Helicobacter is disappearing extremely rapidly. In the NHANES IV study, less than six percent of US children had Helicobacter, and probably two generations ago it was 70 percent,” said Blaser.
“So, this is a huge change in human micro-ecology. The disappearance of an organism that’s been in the stomach forever and is dominant is likely to have consequences. The consequences may be both good — less likelihood of gastric cancer and ulcers later in life — and bad: more asthma early in life,” he added.
“Helicobacter pylori Colonization Is Inversely Associated with Childhood Asthma.”
Yu Chen, and Martin J Blaser.
Published Online July 2008.
DOI: 10.1086/590158
Sources: Journal Abstract, NYU press release.
Written by: Catharine Paddock, PhD