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Science Review: Probiotic Research and Clinical Benefits

Introduction

The body of probiotic research, as well as probiotic use, is growing. Data from the 2012 National Health Interview Survey (NHIS) show probiotics to be the third most commonly used dietary supplement other than vitamins and minerals, and the use of probiotics quadrupled between 2007 and 2012.1 As public awareness of probiotics continues to expand, it is important for healthcare practitioners to increase their understanding of probiotic research and literacy surrounding probiotic definitions and use.2 In 2013, the International Scientific Association for Probiotics and Prebiotics (ISAPP) updated the definition of probiotics to “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.”3 This definition is consistent with the World Health Organization (WHO) and Food and Agriculture Organization (FAO) definition4 and helped to minimize confusion and bring clarity to researchers, consumers, industries, regulatory agencies, and healthcare professionals. For example, although fermented foods and commensal microorganisms in the gut may be sources for probiotic strains, until these strains have been clinically studied and adequately characterized for content, stability, and health effects at the sufficient amount, they cannot be called “probiotics.”

 

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Research highlights

✓ Probiotics are live microorganisms that provide health benefits to
the host when ingested in adequate amounts
✓ Mechanisms underlying the effects of probiotics include
supporting barrier function, competitive adherence to the mucosa
and epithelium, antimicrobial activity, production of beneficial
compounds, and modulation of the immune system to convey an
advantage to the host
✓ Strain-specific probiotics have demonstrated significant potential
as therapeutic options for the prevention and treatment of several
indications, such as:

• Reducing pain after colonoscopy
• Reducing traveler’s diarrhea
• Decreasing pain during IBS
• Decreasing duration of the common cold

✓ Appropriate strain and dose selection for specific clinical
applications is critical for eliciting positive outcomes

Clinical benefits

When evaluating clinical studies, the condition and ages of the population treated, the dose used, the methods used to evaluate outcomes, and many other factors need to be examined to understand the strength and specific relevance of the evidence.11 Clinical evidence pertaining to probiotics can be diverse, ranging from prevention of disease or side effects of standard disease therapies to the treatment of acute or chronic diseases or relief of disease symptoms.11 It is important to recognize that some published meta-analyses and reviews do not specify strains or doses and may pool probiotics inappropriately at the genus level.

Identification and safety

The ISAPP guidelines for defining probiotics provide a benchmark for the differentiation of probiotics based upon levels of scientific evidence for their efficacy.3 The establishment of standards and guidelines represents a necessary first step in helping ensure that probiotic use is safe and effective important for clinicians and patients alike.5 For example, a report of the Joint FAO/WHO working group on probiotics in food set forth guidelines that probiotic strains be characterized at a minimum with a series of tests, including resistance to antibiotics, production of metabolites, production of toxins, hemolytic activity, side effects in human studies, and postmarket adverse events, with an additional recommendation to evaluate whether immunocompromised animals would be infected by the probiotic strain.Further, the European Union assembled a panel to assess and substantiate methodologies to ensure the highest possible standards of products marketed as probiotics. These guidelines extended the FAO and WHO recommendations to include the stability of the strain through the gastrointestinal (GI) tract, resistance to technological processing, shelf life stability, and labeling direction.6

Probiotic consumption is considered safe, and complications are rare for most populations.7 Epidemiologic evidence suggests no overall increase in population risk or adverse events in healthy individuals based on usage data.8,9 However, some reports indicate probiotics should be avoided in certain at-risk populations.10 Safety concerns include the following:

• Common side effects are typically transient but include gas and bloating
• The critically ill and those who are severely immunocompromised should avoid probiotics

Clinically studied doses for efficacy

A meta-analysis of probiotic trials demonstrated that efficacy is specific both to the indication as well as to the specific strain.11 Therefore, each strain and each dose requires clinical evidence for demonstration of efficacy. Furthermore, increasing the dose of the probiotic strain or combination of strains may or may not be more effective.12 In the case of adult inpatients receiving antibiotic therapy, GI symptoms decreased more significantly with a higher dose (17 billion CFU v. 4.17 billion CFU) of a four-strain probiotic combination (L. acidophilus NCFM, L. paracasei Lpc-37, B. lactis Bi-07, and B. lactis BI-04), indicating a dose-dependent effect for antibiotic-associated diarrhea (AAD).13 In addition, whole gut transit time (WGTT) and the frequency of functional GI symptoms were improved in a dose-dependent manner in patients administered 1.8 and 17 billion CFU of B. lactis HN019.14 Conversely, in patients with irritable bowel syndrome (IBS), a metaanalysis demonstrated that a single strain, low dose, and short treatment duration were more effective with respect to overall symptom response and quality of life.15 Similarly, 5 and 50 billion CFU of B. lactis HN019 had similar effectiveness on enhancing cellular immunity in the elderly.16 Thus, increasing the dose does not always result in more significant benefits.

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