It is not possible to state one dose for all probiotics. The dose must be specific to the product based on the benefits shown to be delivered at that dose in clinical trials. 

What Happens Once You Consume a Probiotic? 

The probiotic definition does not dictate a method of administration. Probiotics are being studied as a topical application for skin and an intravaginal application for urogenital infections. Most probiotics are taken orally, as foods or dietary supplements. Probiotic strains—even those isolated from human sources—generally do not last in a consumer’s intestinal tract for more than 2 weeks. This is because the normal microbes colonizing the digestive tract effectively prevent transient microbes from colonizing. Therefore, regular consumption of probiotics is necessary for continued benefits. The benefits that probiotics impart are incurred during their transit through the alimentary canal, including the mouth, stomach, small intestine, and large intestine, into a woman’s vaginal tract, and onto a newborn’s body. Mucosal interfaces along this path provide a means for probiotics to intimately interact with the host immune system, and the relatively slow transit through the colon provides enough time for dynamic metabolic activity that can affect colonizing microbes or host cells, and interaction with the CNS through the vagus nerve. Bron and colleagues2 provide an excellent review of probiotic mechanisms of action.

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Safety of Probiotics

Probiotics have been studied and used safely for decades. Many probiotics were isolated either from the native microbiota of healthy humans or from fermented foods. Thus, traditional probiotics comprise genera and species with a history of safe use. They are included on the European Qualified Presumption of Safety list for live microbes used in foods. Many probiotic strains have also undergone testing and review and have fulfilled the FDA status of “Generally Recognized as Safe” for use in foods. Although more complete reporting of safety end points in published studies would be useful, most experts in the field recognize that use of common probiotic Lactobacillus and Bifidobacterium species and S cerevisiae (biovariant boulardii) in the generally healthy population carries little risk. Newly proposed probiotic species that do not have a history of safe use, such as those identified through the human microbiome project, will require safety assessments. In addition, use of probiotics in vulnerable populations may require more stringent quality standards than those for use in the general population. 

Benefits of Probiotics

Studies have provided evidence for efficacy of some probiotics for different health and clinical conditions, including antibiotic-associated diarrhea, digestive symptoms (including those associated with irritable bowel syndrome), necrotizing enterocolitis, respiratory tract infections, acute pediatric diarrhea, and pediatric eczema. Health care providers in the United States and elsewhere use probiotics in their practices, even though the quality of evidence varies and additional, well-controlled human trials would enable stronger conclusions on best probiotic use. Hospital formularies often carry one or more probiotics, but the ones carried are not necessarily probiotics with best evidence. Clinical use of probiotics for vulnerable patients (such as premature infants or critical care patients) must be done with care. Probiotics for such uses should have demonstrated safety for the target patient population and should meet high quality standards. In cases in which patient vulnerability is not a concern, probiotics may be a low-risk option for conditions lacking suitable, safe interventions. 

Research on new applications for probiotics includes use for different mental health conditions, such as depression, anxiety, and autism, and some metabolic syndrome applications, such as weight management, cholesterol lowering, and insulin sensitivity. 

See Table 1 for a list of end points with positive outcomes for probiotics.

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