National Institutes of Health • National Center for Complementary and Alternative Medicine
Spotlight on a Modality: Oral Probiotics:
What the Science Says
Advances in our understanding of the human microbiome in health and disease have also stimulated great interest and activity among researchers in the potential of probiotics to benefit human health. Probiotic research is moving forward on two fronts: basic science and clinical trials to evaluate the safety and efficacy of probiotics for various medical conditions. While definitive clinical evidence to support using specific probiotic strains for specific health purposes is generally lacking, there is preliminary evidence for several uses of probiotics, and more studies are under way.
- A recent Cochrane review of the scientific evidence on the effectiveness of probiotics in acute infectious diarrhea concluded that there was evidence that probiotics may shorten the duration of diarrhea and reduce stool frequency but that more research was needed to establish exactly which probiotics should be used for which groups of people.
- In 2008, the journal Clinical Infectious Diseases published a special issue on probiotics, which included an overview of clinical applications. Based on a review of selected studies, the authors classified several applications according to the strength of evidence supporting the efficacy of probiotics in prevention and/or treatment.
- For example, the authors concluded that strong evidence exists for acute diarrhea and antibiotic-associated diarrhea, and substantial evidence exists for atopic eczema (a skin condition most commonly seen in infants).
- Promising applications include childhood respiratory infections, tooth decay, nasal pathogens (bacteria harbored in the nose), gastroenteritis relapses caused by Clostridium difficile bacteria after antibiotic therapy, and inflammatory bowel disease.
- Studies also indicate that probiotics may reduce side effects associated with treatment for Helicobacter pylori infection, the cause of most stomach ulcers.
- A systematic review suggests that there is strong evidence that probiotics may reduce the risk of necrotizing enterocolitis, a severe intestinal condition of premature newborns.
- Other potential future applications include use in reducing cholesterol levels, treating obesity, and managing irritable bowel syndrome.
Side Effects and Risks
It appears that most people do not experience side effects from probiotics or have only mild gastrointestinal side effects such as gas. But there have been some case reports of serious adverse effects, and research on safety is ongoing.
- A 2011 Agency for Healthcare Research and Quality assessment of the safety of probiotics, partly funded by NCCAM, concluded that the current evidence does not suggest a widespread risk of negative side effects associated with probiotics.
- Similarly, a 2008 review of probiotics safety noted that Lactobacillus rhamnosus GG has been widely studied in clinical trials for a variety of conditions and generally found to be safe.
- However, the data on safety, particularly long-term safety, are limited, and the risk of serious side effects may be greater in people who have underlying health conditions.
- A recent review of Lactobacillus and Bifidobacterium noted that the long-term, cumulative effects of probiotics use, especially in children, are unknown, and also pointed to evidence that probiotics should not be used in critically ill patients.
- Concerns have also been raised about the quality of some probiotic products. Some products have been found to contain smaller numbers of live microorganisms than expected. In addition, some products have been found to contain bacterial strains other than those listed as ingredients.
Talking With Your Patients About Probiotics
Our understanding of probiotics is a work in progress. If a patient is considering probiotics, be sure to explain that:
- Probiotic products generally appear to be safe, but scientific evidence supporting specific uses is still limited, and the FDA has not approved any health claims for probiotics.
- Probiotic products may contain different types of probiotic bacteria and have different effects in the human body. The effects also may vary from person to person.
- Patients should not replace scientifically proven treatments with unproven products and practices. They should not use a complementary health product, such as probiotics, as a reason to postpone seeing their health care provider about any health problem.
- Anyone with a serious underlying health problem should be monitored closely for potential negative side effects while taking probiotics.
NCCAM Clinical Digest is a service of the National Center for Complementary and Alternative Medicine, NIH, DHHS. NCCAM Clinical Digest, a monthly e-newsletter, offers evidence-based information on CAM, including scientific literature searches, summaries of NCCAM-funded research, fact sheets for patients, and more.
The National Center for Complementary and Alternative Medicine is dedicated to exploring complementary and alternative healing practices in the context of rigorous science, training CAM researchers, and disseminating authoritative information to the public and professionals. For additional information, call NCCAM's Clearinghouse toll-free at 1-888-644-6226, or visit the NCCAM Web site at nccam.nih.gov. NCCAM is 1 of 27 institutes and centers at the National Institutes of Health, the Federal focal point for medical research in the United States.
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