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Can antacids boost allergy risk?

People prescribed antacids are roughly twice as likely to later be offered drugs for respiratory allergies, such as hay fever or asthma, a new study finds. The research doesn’t prove that taking antacids causes allergies, but it adds to a growing body of evidence suggesting a connection between the two.

“I would not bet my house that this is a true phenomenon, but there is ample evidence” that it is, says infectious disease physician Edward Mitre of the Uniformed Services University in Bethesda, Maryland. Mitre was not part of this study, but he published research last year reporting a similar pattern in infants prescribed antacids.

Antacids, such as Nexium and Prilosec, work by decreasing acid production in the stomach. They’re often used for gastrointestinal reflux, which occurs when acid flows upward into the esophagus from the stomach and causes the uncomfortable sensation known as heartburn.

Antacids are typically considered low risk. But in recent years, some experts have worried about overuse. There are also indications that the drugs may alter immune function and heighten the chance of certain bacterial infections, perhaps because they change the balance of bacteria in the gut. This shift may compromise the immune system’s ability to react to invaders, making it easier for certain foreign bacteria to get a foothold in the body.

More than a decade ago, Erika Jensen-Jarolim began to wonder whether antacids could also spark allergies. A friend had shared unexpected news: He had abruptly developed a rare allergy to beluga caviar. Jensen-Jarolim, a clinical immunologist and allergy researcher at the Medical University of Vienna, then learned that her friend also took proton-pump inhibitors and sucralfate, both popular classes of antacids. Because the medicines blunt stomach acid production, food proteins aren’t broken down as much as they usually are. Those proteins are able to sensitize the immune system and trigger an allergic reaction in someone with a food allergy. Could these larger-than-usual protein pieces prime the immune system, making an allergic response more likely?

Jensen-Jarolim and her colleagues began to study mouse models of food allergy, beginning by creating a mouse allergic, like her friend, to beluga caviar. They found that proteins that were largely intact were much more likely to trigger an allergic reaction in the rodents than proteins that were degraded by stomach acid.

In the new study, the team turned to health insurance claim data covering nearly all of the more than 8 million people in Austria. The researchers analyzed prescription information from 2009 to 2013, focusing on antacids and allergy medications. On average, someone prescribed an antacid was about twice as likely to later be prescribed an antiallergy drug, such as an anti-histamine, as compared with a person who wasn’t offered an antacid, the researchers report today in Nature Communications. People over age 60 were five times more likely to get an antiallergy drug prescription if they had earlier been prescribed an antacid than if they hadn’t—with an absolute risk of almost 5% versus almost 1%. For those under 20 years old, the risk increase was much smaller, only about 1.5 times as high—almost 7% versus almost 5%.

Experts caution that the numbers do not definitively show that antacids can cause allergies. “What this shows are that two types of prescriptions for medications track in the same direction,” says Matthew Greenhawt, a pediatric allergist-immunologist at Children’s Hospital Colorado in Denver. “It doesn’t imply” that taking an antacid will later cause allergies, he says.

Jensen-Jarolim herself notes that the information she had was limited. For example, the data from insurance companies traced only what was prescribed, not whether patients actually took those drugs. The information also didn’t include health histories, such as which allergies patients were offered treatment for. Her study, too, focused on respiratory allergies, whereas her earlier animal models probed food allergies. She’s interested in now turning to a mouse model of respiratory allergy to see what antacids might do to that allergic response.

Mitre cautions that even if antacids increase one’s risk of allergies, people suffering from reflux shouldn’t necessarily stop using these medications. Doctors, he says, “just might need to reconsider how freely we prescribe them.”