Probiotics have been touted as beneficial for overall health but doubts have been raised by two back-to-back studies published Thursday that suggest they may not be as effective as previously thought.
Almost 4 million adults in the U.S. consume probiotics with the belief that the supplement will improve their immune system, counteract the effects of antibiotics and prevent disease, Forbes noted.
Roughly 60 percent of physicians recommend patients consume probiotic foods or supplements, a recent study found.
Additionally, a national health survey found that the use of probiotics or prebiotics by adults in the U.S. in 2012 was four times higher than in 2007.
Now researchers at the Weizmann Institute of Science in Tel Aviv, who published both studies in the journal Cell, suggest that probiotics may not be as beneficial as previously thought, and could even pose health risks.
In the first study, 15 volunteers were split into two groups and given either an 11-strain probiotic or placebo pill, according to the institute.
Over the course of several weeks, researchers monitored their response and found the results to be highly individualized.
The volunteers fell into two main groups: The "persisters" whose guts hosted the probiotic microbes, and the "resisters" who expelled the microbiomes.
"Our results suggest that probiotics should not be universally given to the public as a 'one size fits all' supplement," said Prof. Eran Elinav, who was involved in the study.
In the second study, researchers set about determining whether probiotics could counteract the effect of antibiotics in the gut.
Antibiotics were administered to 21 volunteers, who were then assigned to three groups.
The team found that the probiotics' gut colonization prevented their microbiome from returning to their normal pre-antibiotic state months later.
Elinav noted that the results "reveal a new and potentially alarming adverse side effect of probiotic use with antibiotics that might even bring long-term consequences."
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