TUESDAY, July 17, 2018 (HealthDay News) -- Probiotics have become a trendy dietary supplement, with more and more people popping bacteria-laden capsules to try to improve their gut health.
But these supplements could harm some patients, and researchers have done a poor job tracking their safety, a new review argues.
Reporting of side effects is often "missing, insufficient or inadequate" in clinical trials aimed at assessing the value of probiotics, according to findings published July 16 in the Annals of Internal Medicine.
In fact, one-third of probiotics studies provided no information at all on harmful effects, even to note there were none, the French researchers found.
"I agree that we don't understand the harms possible from this poorly regulated area of medicine," said Dr. Arun Swaminath, director of the inflammatory bowel disease program at Lenox Hill Hospital in New York City.
"What's really fascinating isn't that harms were poorly described and infrequently reported, but that many researchers in the field thought it unnecessary," he said.
A person's digestive system contains tens of trillions of bacteria, and we're only now learning of the many subtle ways in which these microscopic bugs influence our overall health.
Probiotics are promoted as a way to improve your gut health by introducing healthy bacteria into your system, according to the American Gastroenterological Association (AGA).
Most often probiotic supplements contain bacteria, but they also can include other organisms such as yeast, the AGA says.
Possible benefits of probiotics include boosting your immune system, warding off infection and preventing the spread of harmful bacteria in your gut, according to the AGA.
But potential harms could come from using probiotics, particularly for people who are sick or have a compromised immune system, according to the researchers behind the new evidence review. They were led by Aida Bafeta, from Paris Descartes University.
Anecdotal reports have linked probiotics to systemic infections in some patients, the researchers said. Heart and blood infections, in particular, have occurred after patients took probiotics.
Experts also are concerned that probiotics might harm a person's metabolism, or overstimulate the immune system.
To see whether these potential harms are being tracked, the French team reviewed 384 clinical trials aimed at testing the effectiveness of probiotics, prebiotics and synbiotics.
While probiotics add bacteria to a person's system, prebiotics are nutrients that promote the growth of gut bacteria. Synbiotics are foods or dietary supplements that contain both probiotics and prebiotics.
Safety results were not reported in 37 percent of the trials included in the evidence review, researchers found. Harm-related data were reported in only 28 percent of studies.
Only 1 in every 5 clinical trials noted the number of serious adverse events that occurred, the review said.
"Some people have a perception that probiotics are healthy no matter what," said Dr. Joshua Novak, an assistant professor of medicine in the division of gastroenterology at the Icahn School of Medicine at Mount Sinai in New York City.
These researchers are suggesting that outcomes should be reported, Novak continued. "Even if there are none at all, they should be reported as such," he said.
Another U.S. expert made an important observation.
The French researchers "did not find evidence suggesting that these products are unsafe," said Dr. Geoffrey Preidis, an assistant professor with the Baylor College of Medicine in Houston.
"Rather, they highlight the need to report safety data more rigorously in the future," Preidis said. "Although we still generally consider probiotics, prebiotics and synbiotics to be safe for most people, these findings reiterate the importance of speaking to one's doctor before starting a new microbiome-targeting therapy."
Tracking potential harms is particularly important to protect sick people who are more vulnerable to getting an infection or having their immune system turn on them, Novak said.
He said he would not recommend probiotics as a first-line treatment for most inflammatory bowel diseases in most patients.
Novak added that probiotics are unnecessary for people who eat healthily.
"For the average patient, I would recommend just eating a well-balanced healthy diet rich in fruits and vegetables, fiber-rich foods and lean cuts of protein," Novak said. "Fiber is a prebiotic, which is great and can help promote a good microbiome."
The American Gastroenterological Association has more about probiotics.