Over half of common probiotics may be contaminated with gluten, according to researchers at the Celiac Disease Center at Columbia University Medical Center (CUMC).

While gluten only affects a certain part of the population — people with celiac disease, or non-celiac gluten sensitivity — the authors argue in a new study that having higher amounts of the protein in supplements could be harmful to people’s health. In the study, researchers analyzed 22 probiotics, and discovered that 12 of them (55 percent) contained traces of gluten. A protein found in wheat, rye, and barley, gluten must be eliminated from the diets of people who have celiac disease, because it causes chronic pain, bowel problems, and even a greater risk of cancer.

“Many patients with celiac disease take dietary supplements, and probiotics are particularly popular,” Dr. Samantha Nazareth, a gastroenterologist at CUMC and an author of the study, said in the press release. “We have previously reported that celiac patients who use dietary supplements have more symptoms than non-users, so we decided to test the probiotics for gluten contamination.”

To be considered “gluten-free” by FDA standards, a product must contain less than 20 parts per million of the protein. However, four of the probiotics researched in the study contained more than 20 parts per million. The authors argue that there should be stricter standards for “gluten-free” labels when it comes to probiotics — since many celiac patients use supplements that include probiotics in their diets.

“We have been following reports in the scientific literature and news media on inaccurate labeling of nutritional supplements, and it appears that labels claiming a product is gluten-free are not to be trusted, at least when it comes to probiotics,” Dr. Peter Green, professor of medicine and director of the Celiac Disease Center, said in the press release. “This is a potential hazard for our patients, and we are concerned.”

Researchers aren’t certain how harmful excess amounts of gluten in probiotics might be to celiac patients, but it’s enough to cause concern. “Why is there any gluten in these products?” Dr. Benjamin Lebwohl, assistant professor of medicine and epidemiology at the Celiac Disease Center and an author of the study, said in the press release. “Why should the consumer pay any attention to gluten-free labeling on such products? And given the great consumer interest in probiotics, will regulatory bodies take action to protect the public?”

Probiotics are live bacteria that are found in various foods including yogurt, kombucha, and fermented foods. They occur naturally in your digestive system and help keep your gut flora in balance, which is why many people take them as supplements. However, gluten sensitivity shouldn’t be taken lightly, and companies will have to be more careful with “gluten-free” labels.