Probiotics are a multibillion-dollar industry with marketing claims of being an effective treatment for a multitude of ailments, including diarrhea. However, findings from a new study from the University of Calgary show the popular product has no effect on gastroenteritis, commonly yet erroneously called the stomach flu, in children.

"We studied the effects of giving probiotics to hundreds of children whose parents brought them into emergency departments across the country suffering from vomiting and diarrhea," says Dr. Stephen Freedman, MD, pediatric emergency medicine physician with Alberta Health Services, holder of the Alberta Children's Hospital Foundation Professorship in Child Health & Wellness and member of Cumming School of Medicine's Alberta Children's Hospital Research Institute. "We found no evidence that probiotics had any effect on reducing symptoms, or helping with recovery."

Freedman led a six-site Canadian study that included almost 900 children. He was also the co-principal investigator on a 10-site, concurrently conducted study in the United States, led by Dr. David Schnadower, MD that recruited almost 1,000 children. Findings from both studies will be published in the New England Journal of Medicine Thursday, November 22.

"There were smaller trials that had shown promising results. We wanted to replicate these findings on a large scale to see whether the age of the patient, the type of infection, and the use of antibiotics or length of time a child had the illness would affect the response to probiotics," says Schnadower, MD, who conducted the research as a professor of pediatrics at Washington University School of Medicine in St. Louis and is now a professor at University of Cincinnati College of Medicine. "The findings in both studies were consistently negative regardless of how the data were analyzed."

Researchers tested two commercially available brands of probiotics. Recruitment for the Canadian double-blind randomized study began in 2013. Children ranged in age from three to 48 months. Half of the children received probiotics while the other half received a placebo.

"These findings, taken together, are very powerful. The findings show that children treated with probiotics have the exact same outcomes across a large range of symptoms, as those given placebo -- the probiotics had no effect," says Freedman, who is also a member of the O'Brien Institute for Public Health at the Cumming School of Medicine. "The results deliver a clear message that we need to question the role and benefits of probiotics for other health applications using large, patient oriented, rigorous clinical trials."

Probiotics are generally considered safe to use. They are classified as food ingredients in Canada and can be sold as natural health products. As such, they do not require the same rigorous scientific testing that medications require, such as multiple clinical trials, in order to make beneficial claims. "Until now, most studies into the effects of probiotics have been small and industry funded," says Freedman. "In order to better serve families we need independent research to either prove or disprove the claims marketers are making on health care products."

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The Canadian research was supported by the Canadian Institutes of Health Research (CIHR). The U.S. study was supported by the National Institutes of Health (NIH).