Study: How Acid Reflux May Trigger Asthma

Researchers at Duke University Medical Center may be one step closer to learning the answer to a frequently asked questions: Why do so many patients with asthma also suffer from gastroesophageal reflux disease.

As far back as the 1970s physicians have noted a relationship between asthma and GERD. Studies have shown that at least 50%, and as much as 90%, of patients with asthma also experienced some symptoms of GERD.

One puzzling aspect is whether GERD caused asthma in these patients, or if it was the other way around, with the asthma causing GERD symptoms. Physicians wondered if there was a shared mechanism at the root of both conditions that caused them to develop together. Now they have more insight into the matter.

Dr. Shu Lin, an assistant professor of surgery and immunology at Duke, worked with laboratory mice and discovered that when the mice aspirated stomach fluid, there were changes in the immune symptoms of the mice. These changes can stimulate the development of asthma.

When humans experience acid reflux, stomach fluids will back up into the esophagus. Sometimes the stomach fluids can be breathed (aspirated) into the lungs. To mimick this in the mice, the researchers inserted miniscule amounts of gastric fluid into the lungs of the mice. This procedure with the mice was continued over a period of eight weeks. At the end of the eight weeks their immune systems were compared with those of mice that were exposed to allergens but not to gastric fluid.

The immune systems of the two sets of mice responded very differently. Those that had the gastric fluid in their lungs developed what researchers call a T-helper type 2 response, a type of immune system reaction characteristic of asthma. The other mice responded in a more balanced manner, mounting an immune reaction consisting of both T-helper type 1 and T-helper type 2 responses.

Dr Lin stated, "These data suggest that chronic micro-aspiration of gastric fluid can drive the immune system toward an asthmatic response."

William Parker, an assistant professor of surgery at Duke and a co-author of the study, pointed out that this doesn't mean everyone with GERD will also suffer from asthma, but that it may mean that people with GERD may be more likely to develop asthma.

If a patient has both GERD and asthma, there are ways a patient can reduce reflux symptoms that may trigger asthma or asthmatic episodes. These include: Lifestyle modifications and dietary changes.