Probiotic and prebiotic studies lack safety data, says review


A systematic review in the Annals of Internal Medicine says that hundreds of published probiotic and prebiotic studies failed to report important safety data.

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A systematic review in the Annals of Internal Medicine says that hundreds of published probiotic and prebiotic studies failed to report important safety data.1 Industry leaders are expressing disagreement with the findings or at least what they imply.

“An absence of [safety] data does not signify the presence of safety concerns,” said the Council for Responsible Nutrition (Washington, DC) in a press release. “It simply means we need to be better at reporting this crucial information.”

A total of 384 trials were evaluated for the presence of “harms” data in the review. Trials featured probiotics, prebiotics, and synbiotics (a mix of pro- and prebiotics). A majority (69%) were on probiotics. The researchers determined that 106 trials presented no “harms-related data,” 142 presented no “safety results,” and 309 failed to provide the number of serious adverse events. An article about the Annals study published in The BMJ (formerly the British Medical Journal) reports that only 2% of the studies provided safety data deemed adequate by the authors.2

The Annals authors concluded with: “We cannot broadly conclude that these interventions are safe without reporting safety data.”

However, probiotics and prebiotics do have a substantial history of use, and many trials suggest they can confer health benefits. The Natural Products Association (Washington, DC) said in a press statement that FDA considers probiotics to be safe and “…robust adverse event-reporting systems are in place to monitor the use of probiotic and prebiotic supplements.”

FDA says that “over-the-counter probiotics are generally viewed as safe,” but the agency has mentioned a need for better testing of impurities in these ingredients.3 Still, FDA has allowed manufacturers to self-affirm probiotics and prebiotics as GRAS. Here’s what the NIH National Center for Complementary and Integrative Health has to say about probiotics:

“In healthy people, probiotics usually have only minor side effects, if any. However, in people with underlying health problems (for example, weakened immune systems), serious complications such as infections have occasionally been reported.”4

A lack of safety reporting would be a reasonable concern. Future clinical could benefit from gathering and sharing such information. In light of the recent review, it will be interesting to see how future studies on probiotics, prebiotics, and synbiotics are designed to eliminate safety concerns and clarify who may want to avoid these products.


  1. Bafeta A et al. “Harms reporting in randomized controlled trials of interventions aimed at modifying microbiota: a systematic review.” Annals of Internal Medicine. Published online July 17, 2018.
  2. Mayor S. “Sixty seconds on…probiotics.” The BMJ. Published online July 17, 2018.
  3. U.S. Food and Drug Administration. “FDA developing improved methodology for determining purity of probiotic products." Accessed July 20, 2018.
  4. NIH National Center for Complementary and Integrative Health. “Probiotics: In depth." Accessed July 20, 2018.
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