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In recent years there has been a surge in research investigating the human microbiome. Each individual has their own microbiota, the collection of microorganisms that colonise the human body, including bacteria, yeasts, fungi, and viruses, the majority of which reside in the gut. The microbiome describes the collection of genes within these microorganisms. Microbiomes are unique to the individual, and have a role in health and disease.1 There is incredible public interest in how the microbiome may be modulated to improve health. Probiotics have been defined by the World Health Organization (WHO) as “live microorganisms that, when administered in adequate amounts confer a health benefit to the host”. This definition means that products without a proven health benefit should not be labelled as probiotic; however, those who market probiotic products do not necessarily adhere to this definition. This is at least partly because there is no standardised process to define a ‘health benefit’ in this context. In this article, we refer to probiotics as those marketed as such.

Probiotics have been consumed for thousands of years in fermented food such as cheese, wine and bread.2 These foods were believed to confer health benefits; how they did, however, was unknown until the nineteenth century. In 1930, Minoru Shirota isolated the bacteria Lactobacillus casei strain Shirota, from the human intestine and developed it into the first commercially available probiotic product—Yakult®, a fermented milk drink.2 Since then, the probiotic market has exploded with a variety of products, including drinks, yoghurts, tablets and other food products containing a variety of bacterial strains.2 The majority of probiotics contain lactic acid bacteria (LAB) and Bifidobacteria species; both of which are part of the healthy human microbiota and are ubiquitous in food.3

Although promising, the reported health benefits of probiotics have been inconsistent. Some of the studied benefits of probiotic consumption include improvements in intestinal health by: physical exclusion of pathogens by secretion of inhibitory molecules, enhancement of epithelial cell function, modulation of the microbiota and modulation of the immune system.3–5 However, not all clinical trials investigating consumption of live microorganisms have measured the health benefits the same way or defined the same output as a ‘benefit’. These inconsistencies raise doubt for consumers and healthcare professionals.

Probiotics and disease

The main clinical interest in probiotics has been the prevention and treatment of gastrointestinal infections and diseases. Microbiota that deviate from a normal homeostasis have been associated with enhanced risk and severity of disease including autoimmune diseases.6 Inflammatory bowel disease (IBD) has been associated with microbial dysbiosis and an inappropriate immune response causing cytokine-induced epithelial damage.7 Numerous studies in humans and experimental animals have shown that consumption of probiotics may specifically modulate immune responses.8 For example, the replacement of missing Lactobacilli populations in an IL-10 deficient mouse model of colitis resulted in reduced caecal inflammation.9 Consumption of probiotics was associated with a reduction in the incidence of cold and influenza-like symptoms in children,10 and significantly shortened the duration and severity of viral respiratory tract infections in adults.11 A randomised, double-blind placebo-controlled study found that consumption of Lactobacillus plantarum HEAL 9 and Lactobacillus paracasei 8700:2 resulted in a lower incidence of infection with the common cold.12 The potential of probiotics to influence immune responses and the gut microbiota means that probiotic intervention is an attractive option for treatment of inflammatory diseases13 and prevention of infections.

The majority of probiotic marketing is targeted towards healthy individuals, therefore it is important to test the potential health benefits on this population. Changes in immune cell frequencies may indicate an immunological benefit, for example, induction or expansion of regulatory T cells, cells that are important in maintenance of immune tolerance. Takeda et al showed that the probiotic Lactobacillus casei Shirota enhanced Natural Killer cell cytotoxic activity after three weeks consumption.14 In contrast, other studies have found no significant difference in immune cell frequencies following the consumption of probiotics; for example, the consumption of L. paracasei NCC2461 did not alter peripheral blood mononuclear cell (PBMC) frequency or cytokine gene transcription, leading the authors to conclude that gene expression in PBMCs was tightly controlled and not easily manipulated.15

Immune activity of probiotics

The mechanisms of action by which probiotics exert beneficial immune effects are still under active investigation. Studies investigating peripheral immune cells give an indication of the systemic immune responses to probiotics. Investigation of the localised immune response in the human gut is logistically much more challenging. Intestinal epithelial cells are the principal site of contact between probiotic bacteria and the human host. Probiotic bacteria can potentially influence intestinal epithelial cells in multiple ways, for example, by increasing the secretion of mucus by intestinal epithelial cells, which enhances the physical barrier function of the gut,16 and by modulating intestinal epithelial cell signalling pathways. These signalling pathways are involved in regulating proinflammatory genes in epithelial cells and immune cells.

Probiotics in New Zealand

Pharmacies and health stores in New Zealand stock a range of probiotic products, containing a variety of bacterial species. Go Healthy®: Go Probiotic 75 billion contains 12 bacterial species, including Bifidobacterium lactis Bi-07 at a concentration of 10 billion cells (colony forming units (CFU)) per dose. A double blind, placebo-controlled human clinical trial showed that consumption of B. lactis Bi-07 for three weeks by healthy elderly adults significantly enhanced phagocytic activity of monocytes and granulocytes.17 Ethical Nutrients™ Inner Health contains the same bacterial species, B. lactis Bi-07 at a concentration of 15 billion CFU, as well as Lactobacillus acidophilus NCFM at 15 billion CFU. A double blind, placebo controlled study of consumption of this probiotic product by children over a six-month period demonstrated a statistically significant decrease in the incidence of cold and flu-like symptoms compared to the placebo.10 Another Ethical Nutrients™product,IBS Support contains Lactobacillus plantarum 299v at a concentration of 20 billion CFU per dose. Two hundred and fourteen irritable bowel syndrome (IBS) patients were recruited in a placebo-controlled, parallel design study of this product. They were randomised to receive probiotic or placebo for four weeks. This probiotic was shown to provide statistically significant symptom relief, particularly of abdominal pain and bloating.18 Other combination probiotic products available in New Zealand may contain bacterial strains that are completely safe for consumption; however, they may not have been tested in isolation in a human clinical trial to determine health benefits.

Limitations of probiotic trials

Trials investigating the benefits of probiotics usually involve administration of a probiotic or a placebo and collection of faecal and/or blood samples, before and after consumption. Results however, have been inconsistent and occasionally contradictory.19 This is likely due to a number of factors, including cohort size, variation in trial design, treatment duration, patient cohort characteristics, dosage, the use of live probiotics versus killed probiotic components and, especially, comparisons of different probiotic species and strains. Differences observed in the immune modulatory effects of probiotics are frequently bacterial strain specific.8,19 Investigation of the responses of the human host to probiotic consumption requires carefully designed and controlled clinical trials that consider the probiotic(s), the host population and the study design.

Meta-analyses of probiotic trials collate data from multiple studies. These are a powerful statistical analysis tool in many fields of research as they can resolve uncertainty from conflicting results.20 However, this research approach is inappropriate for analysing the health benefits of probiotics if these benefits are species and strain-specific. The term ‘probiotics’ can be a label for a range of different microbial species. The majority of probiotics are gram-positive bacteria, in particular, Lactobacillusspecies.21 There are also gram-negative probiotics available such as Escherichia coli Nissle 191722 and yeasts such as Saccharomyces boulardii.23 The physiological structures of these organisms are different and interact with the human body in distinctive ways.24 Even different strains of the same species can secrete a variety of molecules stimulating a unique response in the host. A meta-analysis study of probiotics for the treatment of IBS pooled studies totaling 20 different strains of bacteria.25 Conclusions from this study could only suggest that probiotic use may be associated with improvement in IBS symptoms, but noted these results should be interpreted with caution due to the variability of trial designs of the included studies.25 Strain-specific benefits cannot be seen when meta-analysis treats all probiotic strains as identical.

Another meta-analysis study, published in 2016, investigated the effect of probiotic supplementation on the faecal microbiota in healthy participants by pooling results from seven randomised control trials. The authors concluded probiotic consumption had no effect on faecal microbiota composition.26 However, the interpretation of this result failed to acknowledge that probiotics do not necessarily need to colonise and have a persistent presence in the gut to offer a health benefit, especially in healthy individuals. For example, transient microbial populations can still stimulate the immune system.27 The meta-analysis highlighted the importance of defining the primary and secondary outcomes in research.26 It may have been more appropriate for faecal composition to be considered as a secondary outcome, and the primary outcome stimulation of immune responses.

The majority of experimental research into the health benefits of probiotics has been conducted on groups of diseased subjects, measuring the effect of the probiotic on disease-related symptoms. These studies are often designed purely for methodological reasons, as significant positive results are easy to identify. Studies of the benefits of probiotics for the healthy population are more complicated, as it is difficult to record significant positive physiological effects when functional abnormalities are not present.28 However, probiotics are principally marketed for use by healthy consumers. A limitation of the ability to measure positive immune effects in a healthy population is the difficulty in measuring significant differences where there is wide natural variation in, for example, immune parameters.

For the beneficial claims of probiotics to gain credibility in the clinical field, future clinical trials may need to be standardised. The only way various probiotic species can be compared is if they are tested in the same way, with primary and secondary outcomes well defined. There are hundreds of species and strains of probiotic bacteria that have not yet been thoroughly researched, but which need to be analysed independently to determine strain specific effects.

An important consideration in trial design is the calculation of the appropriate cohort size in order to obtain sufficient power to detect significance. A limiting factor of this may be that large cohort sizes are required when studying populations with high natural variability. Once the cohort size has been determined and an effective probiotic dose has been established, the test parameters that could be set include the dosing regime (for example, consistent consumption of probiotics for two weeks) and format of delivery (for example as a pill, in milk, yoghurt, as a liquid). Studies should aim to collect multiple faecal samples to indicate viability or colonisation of the probiotic and blood samples to measure systemic immune responses, as well as recording health scores and incidence of sickness. Analysis and outcomes that are reported in a consistent format would allow comparisons across multiple studies. The probiotic benefits should be tested on both healthy and diseased state participants. A problem with investigating probiotic effects on target diseases, such as IBS, is that these diseases are heterogeneous and therefore difficult to categorise. Analysis of probiotics in a standardised way would enable development of a data bank containing effects of all probiotic strains and species and make interpretation of health benefits more straightforward for health professionals and consumers.

Regulation of probiotics

Probiotics are part of a global health supplement industry. Guidelines, regulations and categorisation of probiotics vary from country to country. In New Zealand, probiotics can be sold as a ‘functional food’, a product that serves a physiological role beyond the provision of simple nutrient requirements.29 In the US, probiotics can be sold in a range of categories including dietary supplementation or probiotic drug. If a probiotic is sold as a drug, then it must first undergo the regulatory processes as a drug, and evidence must be supplied for the claimed health benefits. If a probiotic is sold as a dietary supplement, it comes under the umbrella of ‘food’ and does not require FDA approval, which is typical for bacterial genera with a history of use such as Lactobacillus species.30 Next-generation probiotics contain bacteria (such as Akkermansia species) that are not necessarily ubiquitous in food and do not have a history of probiotic use. These products are therefore difficult to both categorise and regulate. As more research of the healthy microbiome is published, new candidate probiotics will also need to be regulated in the absence of historical data. The category in which probiotics are sold determines the claims that can be made surrounding the health benefits. Manufacturers selling probiotics as functional foods can make generalised statements, for example “improves digestive health”. This statement suggests a benefit for probiotic consumption.31 Advertising like this is attractive to consumers and encourages sales.

In New Zealand, companies can base generalised health claims on one of the pre-approved food-health relationships set in Standard 1.2.7 by Food Safety Australia and New Zealand (FSANZ).32 Under this standard, health claims require supporting scientific evidence, but this can be self-substantiated by manufacturers. Companies must notify FSANZ when making a generalised health claim. FSANZ will then publish the health claim; however, they do not guarantee the accuracy of the information in the claim, or take responsibility for enforcing this requirement; their role is solely in public notification. Manufacturers can initiate trials of their own probiotic products, and benefits are marketed directly to consumers. As evidence is not easily accessible to the general public, consumers must trust products have been through the correct regulatory processes to make these claims. This can also cause healthcare professionals to doubt product efficacy and make it difficult to advise patients that enquire about probiotics.

In 2001, the World Health Organization Expert Consultation for the Evaluation of Health and Nutritional Properties of Probiotics developed a set of standardised guidelines for manufacturers to follow during the assessment of probiotic health benefits.30 This was an endeavor to increase integrity of health claims. The guidelines included identification of the genus and species of probiotic, determination of the mechanism of action of the probiotic effect via in vitro analysis; and the verification of probiotic health benefit by a human clinical trial.30 It was then the responsibility of the manufacturers to follow these guidelines and prove the efficacy, however only a few manufacturers followed those guidelines in published literature.

Healthcare professionals and consumers need to be able to assess scientific information to make informed decisions when using probiotics. To address this issue, we would benefit from an online resource which collates and translates the scientific literature on probiotics available in New Zealand into practical, easy to understand clinically relevant information. Such tools have already been created in Canada and the US, for example, the AEProbio Clinical Guide to Probiotic Products.33 In the meantime, consumers and health professionals rely on labelling of probiotic products to facilitate decision making. Interpreting variable labels is difficult; the recommended minimum information is shown in Figure 1.

Figure 1: An example of appropriate labelling on a probiotic product, and guide to interpreting the information.

c

Conclusions

Probiotics contain a variety of bacterial species, and consumers have a diverse gut microbial population that affects their health, and health benefits from probiotics are species- and strain-specific. Personalised probiotics for each individual are a distinct possibility in the future. Standardisation of clinical trial design and reporting would enable the health benefits from probiotic trials to be compared. Healthcare professionals and consumers in New Zealand need accessible, scientifically valid information on the probiotics available here and the ability to interpret product labelling in order to make informed decisions.

Summary

Abstract

Research into the health benefits of probiotics has growing interest. Reported benefits of probiotic consumption range from the improvement of intestinal function to immune support. However, trials of probiotics lack the standardisation required to judge efficacy. It is important to acknowledge that probiotic products include a range of bacterial species and strains that can have varied effects. In this article, we address the importance of correctly interpreting trials of proposed probiotics. We discuss the necessity to treat probiotic bacterial strains independently, and to communicate findings consistently through both data reporting and product labelling. Finally, we propose a new approach to study the health effects of probiotics in the future.

Aim

Method

Results

Conclusion

Author Information

Gemma Laws, MSc Candidate, Department of Microbiology and Immunology, University of Otago, Dunedin; Roslyn Kemp, Associate Professor, Department of Microbiology and Immunology, University of Otago, Dunedin.

Acknowledgements

Correspondence

Roslyn Kemp, Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin.

Correspondence Email

roslyn.kemp@otago.ac.nz

Competing Interests

GAL completed an MSc and was supported by Blis Technologies and Callaghan Innovation during her studies. This manuscript was prepared after submission of the thesis.

  1. Bull MJ, Plummer NT. Part 1: The human gut microbiome in health and disease. Integrative Medicine 2014; 13(6):17–22.
  2. Ozen M, Dinleyici EC. The history of probiotics: the untold story. Beneficial Microbes. 2015; 6(2):159–65.
  3. Ljungh A, Wadstrom T. Lactic acid bacteria as probiotics. Current Issues in Intestinal Microbiology. 2006; 7(2):73–89.
  4. Anderson RC, Cookson AL, McNabb WC, Park Z, McCann MJ, Kelly WJ, et al. Lactobacillus plantarum MB452 enhances the function of the intestinal barrier by increasing the expression levels of genes involved in tight junction formation. BMC Microbiology. 2010; 10(1):316.
  5. Todoriki K, Mukai T, Sato S, Toba T. Inhibition of adhesion of food-borne pathogens to Caco-2 cells by Lactobacillus strains. Journal of Applied Microbiology. 2001; 91(1):154–9.
  6. Sheu B-S, Cheng H-C, Kao A-W, Wang S-T, Yang Y-J, Yang H-B, et al. Pretreatment with Lactobacillus- and Bifidobacterium-containing yogurt can improve the efficacy of quadruple therapy in eradicating residual Helicobacter pylori infection after failed triple therapy. The American Journal of Clinical Nutrition. 2006; 83(4):864–9.
  7. Sartor RB. Mechanisms of Disease: pathogenesis of Crohn’s disease and ulcerative colitis. Nature Clinical Practice Gastroenterology & Hepatology. 2006; 3:390.
  8. Ashraf R, Shah NP. Immune system stimulation by probiotic microorganisms. Critical Reviews in Food Science and Nutrition. 2014; 54(7):938–56.
  9. Madsen KL, Doyle JS, Jewell LD, Tavernini MM, Fedorak RN. Lactobacillus species prevents colitis in interleukin 10 gene–deficient mice. Gastroenterology. 1999; 116(5):1107–14.
  10. Leyer GJ, Li S, Mubasher ME, Reifer C, Ouwehand AC. Probiotic effects on cold and influenza-like symptom incidence and duration in children. Pediatrics. 2009; 124(2):e172–e9.
  11. de Vrese M, Winkler P, Rautenberg P, Harder T, Noah C, Laue C, et al. Probiotic bacteria reduced duration and severity but not the incidence of common cold episodes in a double blind, randomized, controlled trial. Vaccine. 2006; 24(44):6670–4.
  12. Berggren A, Lazou Ahren I, Larsson N, Onning G. Randomised, double-blind and placebo-controlled study using new probiotic lactobacilli for strengthening the body immune defence against viral infections. European Journal of Nutrition. 2011; 50(3):203–10.
  13. Hammer GE, Turer EE, Taylor KE, Fang CJ, Advincula R, Oshima S, et al. Expression of A20 by dendritic cells preserves immune homeostasis and prevents colitis and spondyloarthritis. Nature Immunology. 2011; 12(12):1184–93.
  14. Takeda K, Suzuki T, Shimada S-I, Shida K, Nanno M, Okumura K. Interleukin-12 is involved in the enhancement of human natural killer cell activity by Lactobacillus casei Shirota. Clinical & Experimental Immunology. 2006; 146(1):109–15.
  15. Bourdeau T, Spertini F, Raymond F, Audran R, Gosoniu L, Mercenier A, et al. Transcriptomic analysis of PBMCs from allergic patients after probiotic treatment. Austin Journal of Nutrition and Metabolism. 2017; 4(1).
  16. Caballero-Franco C, Keller K, De Simone C, Chadee K. The VSL#3 probiotic formula induces mucin gene expression and secretion in colonic epithelial cells. American Journal of Physiology-Gastrointestinal and Liver Physiology. 2007; 292(1):G315–G22.
  17. Maneerat S, Lehtinen MJ, Childs CE, Forssten SD, Alhoniemi E, Tiphaine M, et al. Consumption of Bifidobacterium lactis Bi-07 by healthy elderly adults enhances phagocytic activity of monocytes and granulocytes. Journal of Nutritional Science. 2014; 2:e44.
  18. Ducrotté P, Sawant P, Jayanthi V. Clinical trial: Lactobacillus plantarum 299v (DSM 9843) improves symptoms of irritable bowel syndrome. World Journal of Gastroenterology. 2012; 18(30):4012–8.
  19. Kechagia M, Basoulis D, Konstantopoulou S, Dimitriadi D, Gyftopoulou K, Skarmoutsou N, et al. Health benefits of probiotics: A Review. ISRN Nutrition. 2013; 2013:481651.
  20. Gurevitch J, Koricheva J, Nakagawa S, Stewart G. Meta-analysis and the science of research synthesis. Nature. 2018; 555:175.
  21. Preidis GA, Versalovic J. Targeting the human microbiome with antibiotics, probiotics, and prebiotics: gastroenterology enters the metagenomics era. Gastroenterology. 2009; 136(6):2015–31.
  22. Kandasamy S, Vlasova AN, Fischer DD, Chattha KS, Shao L, Kumar A, et al. Unraveling the differences between Gram-positive and Gram-negative probiotics in modulating protective immunity to enteric infections. Frontiers in Immunology. 2017; 8:334.
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  24. Liévin-Le Moal V, Servin AL. Anti-infective activities of lactobacillus strains in the human intestinal microbiota: from probiotics to gastrointestinal anti-infectious biotherapeutic agents. Clinical Microbiology Reviews. 2014; 27(2):167–99.
  25. McFarland LV, Dublin S. Meta-analysis of probiotics for the treatment of irritable bowel syndrome. World Journal of Gastroenterology. 2008; 14(17):2650–61.
  26. Kristensen NB, Bryrup T, Allin KH, Nielsen T, Hansen TH, Pedersen O. Alterations in fecal microbiota composition by probiotic supplementation in healthy adults: a systematic review of randomized controlled trials. Genome Medicine. 2016; 8(1):52.
  27. Ivanov II, Honda K. Intestinal commensal microbes as immune modulators. Cell Host & Microbe. 2012; 12(4):496–508.
  28. Shane AL, Cabana MD, Vidry S, Merenstein D, Hummelen R, Ellis CL, et al. Guide to designing, conducting, publishing and communicating results of clinical studies involving probiotic applications in human participants. Gut Microbes. 2010; 1(4):243–53.
  29. Arora M, Baldi A. Regulatory categories of probiotics across the globe: A review representing existing and recommended categorization. Indian Journal of Medical Microbiology. 2015; 33(5):2–10.
  30. Venugopalan V, Shriner KA, Wong-Beringer A. Regulatory oversight and safety of probiotic use. Emerging Infectious Diseases. 2010; 16(11):1661–5.
  31. Katan MB. Health claims for functional foods: Regulations vary between countries and often permit vague claims. British Medical Journal. 2004; 328(7433):180–1.
  32. FSANZ. Notified food-health relationship to make a health claim: Food Standards Australia New Zealand; 2018 [Available from: http://www.foodstandards.govt.nz/industry/labelling/fhr/Pages/default.aspx
  33. Skokovic-Sunjic D. Clinical Guide to Probiotic Products Available in Canada: AEProbio; 2019 [Available from: http://www.probioticchart.ca

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In recent years there has been a surge in research investigating the human microbiome. Each individual has their own microbiota, the collection of microorganisms that colonise the human body, including bacteria, yeasts, fungi, and viruses, the majority of which reside in the gut. The microbiome describes the collection of genes within these microorganisms. Microbiomes are unique to the individual, and have a role in health and disease.1 There is incredible public interest in how the microbiome may be modulated to improve health. Probiotics have been defined by the World Health Organization (WHO) as “live microorganisms that, when administered in adequate amounts confer a health benefit to the host”. This definition means that products without a proven health benefit should not be labelled as probiotic; however, those who market probiotic products do not necessarily adhere to this definition. This is at least partly because there is no standardised process to define a ‘health benefit’ in this context. In this article, we refer to probiotics as those marketed as such.

Probiotics have been consumed for thousands of years in fermented food such as cheese, wine and bread.2 These foods were believed to confer health benefits; how they did, however, was unknown until the nineteenth century. In 1930, Minoru Shirota isolated the bacteria Lactobacillus casei strain Shirota, from the human intestine and developed it into the first commercially available probiotic product—Yakult®, a fermented milk drink.2 Since then, the probiotic market has exploded with a variety of products, including drinks, yoghurts, tablets and other food products containing a variety of bacterial strains.2 The majority of probiotics contain lactic acid bacteria (LAB) and Bifidobacteria species; both of which are part of the healthy human microbiota and are ubiquitous in food.3

Although promising, the reported health benefits of probiotics have been inconsistent. Some of the studied benefits of probiotic consumption include improvements in intestinal health by: physical exclusion of pathogens by secretion of inhibitory molecules, enhancement of epithelial cell function, modulation of the microbiota and modulation of the immune system.3–5 However, not all clinical trials investigating consumption of live microorganisms have measured the health benefits the same way or defined the same output as a ‘benefit’. These inconsistencies raise doubt for consumers and healthcare professionals.

Probiotics and disease

The main clinical interest in probiotics has been the prevention and treatment of gastrointestinal infections and diseases. Microbiota that deviate from a normal homeostasis have been associated with enhanced risk and severity of disease including autoimmune diseases.6 Inflammatory bowel disease (IBD) has been associated with microbial dysbiosis and an inappropriate immune response causing cytokine-induced epithelial damage.7 Numerous studies in humans and experimental animals have shown that consumption of probiotics may specifically modulate immune responses.8 For example, the replacement of missing Lactobacilli populations in an IL-10 deficient mouse model of colitis resulted in reduced caecal inflammation.9 Consumption of probiotics was associated with a reduction in the incidence of cold and influenza-like symptoms in children,10 and significantly shortened the duration and severity of viral respiratory tract infections in adults.11 A randomised, double-blind placebo-controlled study found that consumption of Lactobacillus plantarum HEAL 9 and Lactobacillus paracasei 8700:2 resulted in a lower incidence of infection with the common cold.12 The potential of probiotics to influence immune responses and the gut microbiota means that probiotic intervention is an attractive option for treatment of inflammatory diseases13 and prevention of infections.

The majority of probiotic marketing is targeted towards healthy individuals, therefore it is important to test the potential health benefits on this population. Changes in immune cell frequencies may indicate an immunological benefit, for example, induction or expansion of regulatory T cells, cells that are important in maintenance of immune tolerance. Takeda et al showed that the probiotic Lactobacillus casei Shirota enhanced Natural Killer cell cytotoxic activity after three weeks consumption.14 In contrast, other studies have found no significant difference in immune cell frequencies following the consumption of probiotics; for example, the consumption of L. paracasei NCC2461 did not alter peripheral blood mononuclear cell (PBMC) frequency or cytokine gene transcription, leading the authors to conclude that gene expression in PBMCs was tightly controlled and not easily manipulated.15

Immune activity of probiotics

The mechanisms of action by which probiotics exert beneficial immune effects are still under active investigation. Studies investigating peripheral immune cells give an indication of the systemic immune responses to probiotics. Investigation of the localised immune response in the human gut is logistically much more challenging. Intestinal epithelial cells are the principal site of contact between probiotic bacteria and the human host. Probiotic bacteria can potentially influence intestinal epithelial cells in multiple ways, for example, by increasing the secretion of mucus by intestinal epithelial cells, which enhances the physical barrier function of the gut,16 and by modulating intestinal epithelial cell signalling pathways. These signalling pathways are involved in regulating proinflammatory genes in epithelial cells and immune cells.

Probiotics in New Zealand

Pharmacies and health stores in New Zealand stock a range of probiotic products, containing a variety of bacterial species. Go Healthy®: Go Probiotic 75 billion contains 12 bacterial species, including Bifidobacterium lactis Bi-07 at a concentration of 10 billion cells (colony forming units (CFU)) per dose. A double blind, placebo-controlled human clinical trial showed that consumption of B. lactis Bi-07 for three weeks by healthy elderly adults significantly enhanced phagocytic activity of monocytes and granulocytes.17 Ethical Nutrients™ Inner Health contains the same bacterial species, B. lactis Bi-07 at a concentration of 15 billion CFU, as well as Lactobacillus acidophilus NCFM at 15 billion CFU. A double blind, placebo controlled study of consumption of this probiotic product by children over a six-month period demonstrated a statistically significant decrease in the incidence of cold and flu-like symptoms compared to the placebo.10 Another Ethical Nutrients™product,IBS Support contains Lactobacillus plantarum 299v at a concentration of 20 billion CFU per dose. Two hundred and fourteen irritable bowel syndrome (IBS) patients were recruited in a placebo-controlled, parallel design study of this product. They were randomised to receive probiotic or placebo for four weeks. This probiotic was shown to provide statistically significant symptom relief, particularly of abdominal pain and bloating.18 Other combination probiotic products available in New Zealand may contain bacterial strains that are completely safe for consumption; however, they may not have been tested in isolation in a human clinical trial to determine health benefits.

Limitations of probiotic trials

Trials investigating the benefits of probiotics usually involve administration of a probiotic or a placebo and collection of faecal and/or blood samples, before and after consumption. Results however, have been inconsistent and occasionally contradictory.19 This is likely due to a number of factors, including cohort size, variation in trial design, treatment duration, patient cohort characteristics, dosage, the use of live probiotics versus killed probiotic components and, especially, comparisons of different probiotic species and strains. Differences observed in the immune modulatory effects of probiotics are frequently bacterial strain specific.8,19 Investigation of the responses of the human host to probiotic consumption requires carefully designed and controlled clinical trials that consider the probiotic(s), the host population and the study design.

Meta-analyses of probiotic trials collate data from multiple studies. These are a powerful statistical analysis tool in many fields of research as they can resolve uncertainty from conflicting results.20 However, this research approach is inappropriate for analysing the health benefits of probiotics if these benefits are species and strain-specific. The term ‘probiotics’ can be a label for a range of different microbial species. The majority of probiotics are gram-positive bacteria, in particular, Lactobacillusspecies.21 There are also gram-negative probiotics available such as Escherichia coli Nissle 191722 and yeasts such as Saccharomyces boulardii.23 The physiological structures of these organisms are different and interact with the human body in distinctive ways.24 Even different strains of the same species can secrete a variety of molecules stimulating a unique response in the host. A meta-analysis study of probiotics for the treatment of IBS pooled studies totaling 20 different strains of bacteria.25 Conclusions from this study could only suggest that probiotic use may be associated with improvement in IBS symptoms, but noted these results should be interpreted with caution due to the variability of trial designs of the included studies.25 Strain-specific benefits cannot be seen when meta-analysis treats all probiotic strains as identical.

Another meta-analysis study, published in 2016, investigated the effect of probiotic supplementation on the faecal microbiota in healthy participants by pooling results from seven randomised control trials. The authors concluded probiotic consumption had no effect on faecal microbiota composition.26 However, the interpretation of this result failed to acknowledge that probiotics do not necessarily need to colonise and have a persistent presence in the gut to offer a health benefit, especially in healthy individuals. For example, transient microbial populations can still stimulate the immune system.27 The meta-analysis highlighted the importance of defining the primary and secondary outcomes in research.26 It may have been more appropriate for faecal composition to be considered as a secondary outcome, and the primary outcome stimulation of immune responses.

The majority of experimental research into the health benefits of probiotics has been conducted on groups of diseased subjects, measuring the effect of the probiotic on disease-related symptoms. These studies are often designed purely for methodological reasons, as significant positive results are easy to identify. Studies of the benefits of probiotics for the healthy population are more complicated, as it is difficult to record significant positive physiological effects when functional abnormalities are not present.28 However, probiotics are principally marketed for use by healthy consumers. A limitation of the ability to measure positive immune effects in a healthy population is the difficulty in measuring significant differences where there is wide natural variation in, for example, immune parameters.

For the beneficial claims of probiotics to gain credibility in the clinical field, future clinical trials may need to be standardised. The only way various probiotic species can be compared is if they are tested in the same way, with primary and secondary outcomes well defined. There are hundreds of species and strains of probiotic bacteria that have not yet been thoroughly researched, but which need to be analysed independently to determine strain specific effects.

An important consideration in trial design is the calculation of the appropriate cohort size in order to obtain sufficient power to detect significance. A limiting factor of this may be that large cohort sizes are required when studying populations with high natural variability. Once the cohort size has been determined and an effective probiotic dose has been established, the test parameters that could be set include the dosing regime (for example, consistent consumption of probiotics for two weeks) and format of delivery (for example as a pill, in milk, yoghurt, as a liquid). Studies should aim to collect multiple faecal samples to indicate viability or colonisation of the probiotic and blood samples to measure systemic immune responses, as well as recording health scores and incidence of sickness. Analysis and outcomes that are reported in a consistent format would allow comparisons across multiple studies. The probiotic benefits should be tested on both healthy and diseased state participants. A problem with investigating probiotic effects on target diseases, such as IBS, is that these diseases are heterogeneous and therefore difficult to categorise. Analysis of probiotics in a standardised way would enable development of a data bank containing effects of all probiotic strains and species and make interpretation of health benefits more straightforward for health professionals and consumers.

Regulation of probiotics

Probiotics are part of a global health supplement industry. Guidelines, regulations and categorisation of probiotics vary from country to country. In New Zealand, probiotics can be sold as a ‘functional food’, a product that serves a physiological role beyond the provision of simple nutrient requirements.29 In the US, probiotics can be sold in a range of categories including dietary supplementation or probiotic drug. If a probiotic is sold as a drug, then it must first undergo the regulatory processes as a drug, and evidence must be supplied for the claimed health benefits. If a probiotic is sold as a dietary supplement, it comes under the umbrella of ‘food’ and does not require FDA approval, which is typical for bacterial genera with a history of use such as Lactobacillus species.30 Next-generation probiotics contain bacteria (such as Akkermansia species) that are not necessarily ubiquitous in food and do not have a history of probiotic use. These products are therefore difficult to both categorise and regulate. As more research of the healthy microbiome is published, new candidate probiotics will also need to be regulated in the absence of historical data. The category in which probiotics are sold determines the claims that can be made surrounding the health benefits. Manufacturers selling probiotics as functional foods can make generalised statements, for example “improves digestive health”. This statement suggests a benefit for probiotic consumption.31 Advertising like this is attractive to consumers and encourages sales.

In New Zealand, companies can base generalised health claims on one of the pre-approved food-health relationships set in Standard 1.2.7 by Food Safety Australia and New Zealand (FSANZ).32 Under this standard, health claims require supporting scientific evidence, but this can be self-substantiated by manufacturers. Companies must notify FSANZ when making a generalised health claim. FSANZ will then publish the health claim; however, they do not guarantee the accuracy of the information in the claim, or take responsibility for enforcing this requirement; their role is solely in public notification. Manufacturers can initiate trials of their own probiotic products, and benefits are marketed directly to consumers. As evidence is not easily accessible to the general public, consumers must trust products have been through the correct regulatory processes to make these claims. This can also cause healthcare professionals to doubt product efficacy and make it difficult to advise patients that enquire about probiotics.

In 2001, the World Health Organization Expert Consultation for the Evaluation of Health and Nutritional Properties of Probiotics developed a set of standardised guidelines for manufacturers to follow during the assessment of probiotic health benefits.30 This was an endeavor to increase integrity of health claims. The guidelines included identification of the genus and species of probiotic, determination of the mechanism of action of the probiotic effect via in vitro analysis; and the verification of probiotic health benefit by a human clinical trial.30 It was then the responsibility of the manufacturers to follow these guidelines and prove the efficacy, however only a few manufacturers followed those guidelines in published literature.

Healthcare professionals and consumers need to be able to assess scientific information to make informed decisions when using probiotics. To address this issue, we would benefit from an online resource which collates and translates the scientific literature on probiotics available in New Zealand into practical, easy to understand clinically relevant information. Such tools have already been created in Canada and the US, for example, the AEProbio Clinical Guide to Probiotic Products.33 In the meantime, consumers and health professionals rely on labelling of probiotic products to facilitate decision making. Interpreting variable labels is difficult; the recommended minimum information is shown in Figure 1.

Figure 1: An example of appropriate labelling on a probiotic product, and guide to interpreting the information.

c

Conclusions

Probiotics contain a variety of bacterial species, and consumers have a diverse gut microbial population that affects their health, and health benefits from probiotics are species- and strain-specific. Personalised probiotics for each individual are a distinct possibility in the future. Standardisation of clinical trial design and reporting would enable the health benefits from probiotic trials to be compared. Healthcare professionals and consumers in New Zealand need accessible, scientifically valid information on the probiotics available here and the ability to interpret product labelling in order to make informed decisions.

Summary

Abstract

Research into the health benefits of probiotics has growing interest. Reported benefits of probiotic consumption range from the improvement of intestinal function to immune support. However, trials of probiotics lack the standardisation required to judge efficacy. It is important to acknowledge that probiotic products include a range of bacterial species and strains that can have varied effects. In this article, we address the importance of correctly interpreting trials of proposed probiotics. We discuss the necessity to treat probiotic bacterial strains independently, and to communicate findings consistently through both data reporting and product labelling. Finally, we propose a new approach to study the health effects of probiotics in the future.

Aim

Method

Results

Conclusion

Author Information

Gemma Laws, MSc Candidate, Department of Microbiology and Immunology, University of Otago, Dunedin; Roslyn Kemp, Associate Professor, Department of Microbiology and Immunology, University of Otago, Dunedin.

Acknowledgements

Correspondence

Roslyn Kemp, Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin.

Correspondence Email

roslyn.kemp@otago.ac.nz

Competing Interests

GAL completed an MSc and was supported by Blis Technologies and Callaghan Innovation during her studies. This manuscript was prepared after submission of the thesis.

  1. Bull MJ, Plummer NT. Part 1: The human gut microbiome in health and disease. Integrative Medicine 2014; 13(6):17–22.
  2. Ozen M, Dinleyici EC. The history of probiotics: the untold story. Beneficial Microbes. 2015; 6(2):159–65.
  3. Ljungh A, Wadstrom T. Lactic acid bacteria as probiotics. Current Issues in Intestinal Microbiology. 2006; 7(2):73–89.
  4. Anderson RC, Cookson AL, McNabb WC, Park Z, McCann MJ, Kelly WJ, et al. Lactobacillus plantarum MB452 enhances the function of the intestinal barrier by increasing the expression levels of genes involved in tight junction formation. BMC Microbiology. 2010; 10(1):316.
  5. Todoriki K, Mukai T, Sato S, Toba T. Inhibition of adhesion of food-borne pathogens to Caco-2 cells by Lactobacillus strains. Journal of Applied Microbiology. 2001; 91(1):154–9.
  6. Sheu B-S, Cheng H-C, Kao A-W, Wang S-T, Yang Y-J, Yang H-B, et al. Pretreatment with Lactobacillus- and Bifidobacterium-containing yogurt can improve the efficacy of quadruple therapy in eradicating residual Helicobacter pylori infection after failed triple therapy. The American Journal of Clinical Nutrition. 2006; 83(4):864–9.
  7. Sartor RB. Mechanisms of Disease: pathogenesis of Crohn’s disease and ulcerative colitis. Nature Clinical Practice Gastroenterology & Hepatology. 2006; 3:390.
  8. Ashraf R, Shah NP. Immune system stimulation by probiotic microorganisms. Critical Reviews in Food Science and Nutrition. 2014; 54(7):938–56.
  9. Madsen KL, Doyle JS, Jewell LD, Tavernini MM, Fedorak RN. Lactobacillus species prevents colitis in interleukin 10 gene–deficient mice. Gastroenterology. 1999; 116(5):1107–14.
  10. Leyer GJ, Li S, Mubasher ME, Reifer C, Ouwehand AC. Probiotic effects on cold and influenza-like symptom incidence and duration in children. Pediatrics. 2009; 124(2):e172–e9.
  11. de Vrese M, Winkler P, Rautenberg P, Harder T, Noah C, Laue C, et al. Probiotic bacteria reduced duration and severity but not the incidence of common cold episodes in a double blind, randomized, controlled trial. Vaccine. 2006; 24(44):6670–4.
  12. Berggren A, Lazou Ahren I, Larsson N, Onning G. Randomised, double-blind and placebo-controlled study using new probiotic lactobacilli for strengthening the body immune defence against viral infections. European Journal of Nutrition. 2011; 50(3):203–10.
  13. Hammer GE, Turer EE, Taylor KE, Fang CJ, Advincula R, Oshima S, et al. Expression of A20 by dendritic cells preserves immune homeostasis and prevents colitis and spondyloarthritis. Nature Immunology. 2011; 12(12):1184–93.
  14. Takeda K, Suzuki T, Shimada S-I, Shida K, Nanno M, Okumura K. Interleukin-12 is involved in the enhancement of human natural killer cell activity by Lactobacillus casei Shirota. Clinical & Experimental Immunology. 2006; 146(1):109–15.
  15. Bourdeau T, Spertini F, Raymond F, Audran R, Gosoniu L, Mercenier A, et al. Transcriptomic analysis of PBMCs from allergic patients after probiotic treatment. Austin Journal of Nutrition and Metabolism. 2017; 4(1).
  16. Caballero-Franco C, Keller K, De Simone C, Chadee K. The VSL#3 probiotic formula induces mucin gene expression and secretion in colonic epithelial cells. American Journal of Physiology-Gastrointestinal and Liver Physiology. 2007; 292(1):G315–G22.
  17. Maneerat S, Lehtinen MJ, Childs CE, Forssten SD, Alhoniemi E, Tiphaine M, et al. Consumption of Bifidobacterium lactis Bi-07 by healthy elderly adults enhances phagocytic activity of monocytes and granulocytes. Journal of Nutritional Science. 2014; 2:e44.
  18. Ducrotté P, Sawant P, Jayanthi V. Clinical trial: Lactobacillus plantarum 299v (DSM 9843) improves symptoms of irritable bowel syndrome. World Journal of Gastroenterology. 2012; 18(30):4012–8.
  19. Kechagia M, Basoulis D, Konstantopoulou S, Dimitriadi D, Gyftopoulou K, Skarmoutsou N, et al. Health benefits of probiotics: A Review. ISRN Nutrition. 2013; 2013:481651.
  20. Gurevitch J, Koricheva J, Nakagawa S, Stewart G. Meta-analysis and the science of research synthesis. Nature. 2018; 555:175.
  21. Preidis GA, Versalovic J. Targeting the human microbiome with antibiotics, probiotics, and prebiotics: gastroenterology enters the metagenomics era. Gastroenterology. 2009; 136(6):2015–31.
  22. Kandasamy S, Vlasova AN, Fischer DD, Chattha KS, Shao L, Kumar A, et al. Unraveling the differences between Gram-positive and Gram-negative probiotics in modulating protective immunity to enteric infections. Frontiers in Immunology. 2017; 8:334.
  23. Kelesidis T, Pothoulakis C. Efficacy and safety of the probiotic Saccharomyces boulardii for the prevention and therapy of gastrointestinal disorders. Therapeutic Advances in Gastroenterology. 2012; 5(2):111–25.
  24. Liévin-Le Moal V, Servin AL. Anti-infective activities of lactobacillus strains in the human intestinal microbiota: from probiotics to gastrointestinal anti-infectious biotherapeutic agents. Clinical Microbiology Reviews. 2014; 27(2):167–99.
  25. McFarland LV, Dublin S. Meta-analysis of probiotics for the treatment of irritable bowel syndrome. World Journal of Gastroenterology. 2008; 14(17):2650–61.
  26. Kristensen NB, Bryrup T, Allin KH, Nielsen T, Hansen TH, Pedersen O. Alterations in fecal microbiota composition by probiotic supplementation in healthy adults: a systematic review of randomized controlled trials. Genome Medicine. 2016; 8(1):52.
  27. Ivanov II, Honda K. Intestinal commensal microbes as immune modulators. Cell Host & Microbe. 2012; 12(4):496–508.
  28. Shane AL, Cabana MD, Vidry S, Merenstein D, Hummelen R, Ellis CL, et al. Guide to designing, conducting, publishing and communicating results of clinical studies involving probiotic applications in human participants. Gut Microbes. 2010; 1(4):243–53.
  29. Arora M, Baldi A. Regulatory categories of probiotics across the globe: A review representing existing and recommended categorization. Indian Journal of Medical Microbiology. 2015; 33(5):2–10.
  30. Venugopalan V, Shriner KA, Wong-Beringer A. Regulatory oversight and safety of probiotic use. Emerging Infectious Diseases. 2010; 16(11):1661–5.
  31. Katan MB. Health claims for functional foods: Regulations vary between countries and often permit vague claims. British Medical Journal. 2004; 328(7433):180–1.
  32. FSANZ. Notified food-health relationship to make a health claim: Food Standards Australia New Zealand; 2018 [Available from: http://www.foodstandards.govt.nz/industry/labelling/fhr/Pages/default.aspx
  33. Skokovic-Sunjic D. Clinical Guide to Probiotic Products Available in Canada: AEProbio; 2019 [Available from: http://www.probioticchart.ca

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In recent years there has been a surge in research investigating the human microbiome. Each individual has their own microbiota, the collection of microorganisms that colonise the human body, including bacteria, yeasts, fungi, and viruses, the majority of which reside in the gut. The microbiome describes the collection of genes within these microorganisms. Microbiomes are unique to the individual, and have a role in health and disease.1 There is incredible public interest in how the microbiome may be modulated to improve health. Probiotics have been defined by the World Health Organization (WHO) as “live microorganisms that, when administered in adequate amounts confer a health benefit to the host”. This definition means that products without a proven health benefit should not be labelled as probiotic; however, those who market probiotic products do not necessarily adhere to this definition. This is at least partly because there is no standardised process to define a ‘health benefit’ in this context. In this article, we refer to probiotics as those marketed as such.

Probiotics have been consumed for thousands of years in fermented food such as cheese, wine and bread.2 These foods were believed to confer health benefits; how they did, however, was unknown until the nineteenth century. In 1930, Minoru Shirota isolated the bacteria Lactobacillus casei strain Shirota, from the human intestine and developed it into the first commercially available probiotic product—Yakult®, a fermented milk drink.2 Since then, the probiotic market has exploded with a variety of products, including drinks, yoghurts, tablets and other food products containing a variety of bacterial strains.2 The majority of probiotics contain lactic acid bacteria (LAB) and Bifidobacteria species; both of which are part of the healthy human microbiota and are ubiquitous in food.3

Although promising, the reported health benefits of probiotics have been inconsistent. Some of the studied benefits of probiotic consumption include improvements in intestinal health by: physical exclusion of pathogens by secretion of inhibitory molecules, enhancement of epithelial cell function, modulation of the microbiota and modulation of the immune system.3–5 However, not all clinical trials investigating consumption of live microorganisms have measured the health benefits the same way or defined the same output as a ‘benefit’. These inconsistencies raise doubt for consumers and healthcare professionals.

Probiotics and disease

The main clinical interest in probiotics has been the prevention and treatment of gastrointestinal infections and diseases. Microbiota that deviate from a normal homeostasis have been associated with enhanced risk and severity of disease including autoimmune diseases.6 Inflammatory bowel disease (IBD) has been associated with microbial dysbiosis and an inappropriate immune response causing cytokine-induced epithelial damage.7 Numerous studies in humans and experimental animals have shown that consumption of probiotics may specifically modulate immune responses.8 For example, the replacement of missing Lactobacilli populations in an IL-10 deficient mouse model of colitis resulted in reduced caecal inflammation.9 Consumption of probiotics was associated with a reduction in the incidence of cold and influenza-like symptoms in children,10 and significantly shortened the duration and severity of viral respiratory tract infections in adults.11 A randomised, double-blind placebo-controlled study found that consumption of Lactobacillus plantarum HEAL 9 and Lactobacillus paracasei 8700:2 resulted in a lower incidence of infection with the common cold.12 The potential of probiotics to influence immune responses and the gut microbiota means that probiotic intervention is an attractive option for treatment of inflammatory diseases13 and prevention of infections.

The majority of probiotic marketing is targeted towards healthy individuals, therefore it is important to test the potential health benefits on this population. Changes in immune cell frequencies may indicate an immunological benefit, for example, induction or expansion of regulatory T cells, cells that are important in maintenance of immune tolerance. Takeda et al showed that the probiotic Lactobacillus casei Shirota enhanced Natural Killer cell cytotoxic activity after three weeks consumption.14 In contrast, other studies have found no significant difference in immune cell frequencies following the consumption of probiotics; for example, the consumption of L. paracasei NCC2461 did not alter peripheral blood mononuclear cell (PBMC) frequency or cytokine gene transcription, leading the authors to conclude that gene expression in PBMCs was tightly controlled and not easily manipulated.15

Immune activity of probiotics

The mechanisms of action by which probiotics exert beneficial immune effects are still under active investigation. Studies investigating peripheral immune cells give an indication of the systemic immune responses to probiotics. Investigation of the localised immune response in the human gut is logistically much more challenging. Intestinal epithelial cells are the principal site of contact between probiotic bacteria and the human host. Probiotic bacteria can potentially influence intestinal epithelial cells in multiple ways, for example, by increasing the secretion of mucus by intestinal epithelial cells, which enhances the physical barrier function of the gut,16 and by modulating intestinal epithelial cell signalling pathways. These signalling pathways are involved in regulating proinflammatory genes in epithelial cells and immune cells.

Probiotics in New Zealand

Pharmacies and health stores in New Zealand stock a range of probiotic products, containing a variety of bacterial species. Go Healthy®: Go Probiotic 75 billion contains 12 bacterial species, including Bifidobacterium lactis Bi-07 at a concentration of 10 billion cells (colony forming units (CFU)) per dose. A double blind, placebo-controlled human clinical trial showed that consumption of B. lactis Bi-07 for three weeks by healthy elderly adults significantly enhanced phagocytic activity of monocytes and granulocytes.17 Ethical Nutrients™ Inner Health contains the same bacterial species, B. lactis Bi-07 at a concentration of 15 billion CFU, as well as Lactobacillus acidophilus NCFM at 15 billion CFU. A double blind, placebo controlled study of consumption of this probiotic product by children over a six-month period demonstrated a statistically significant decrease in the incidence of cold and flu-like symptoms compared to the placebo.10 Another Ethical Nutrients™product,IBS Support contains Lactobacillus plantarum 299v at a concentration of 20 billion CFU per dose. Two hundred and fourteen irritable bowel syndrome (IBS) patients were recruited in a placebo-controlled, parallel design study of this product. They were randomised to receive probiotic or placebo for four weeks. This probiotic was shown to provide statistically significant symptom relief, particularly of abdominal pain and bloating.18 Other combination probiotic products available in New Zealand may contain bacterial strains that are completely safe for consumption; however, they may not have been tested in isolation in a human clinical trial to determine health benefits.

Limitations of probiotic trials

Trials investigating the benefits of probiotics usually involve administration of a probiotic or a placebo and collection of faecal and/or blood samples, before and after consumption. Results however, have been inconsistent and occasionally contradictory.19 This is likely due to a number of factors, including cohort size, variation in trial design, treatment duration, patient cohort characteristics, dosage, the use of live probiotics versus killed probiotic components and, especially, comparisons of different probiotic species and strains. Differences observed in the immune modulatory effects of probiotics are frequently bacterial strain specific.8,19 Investigation of the responses of the human host to probiotic consumption requires carefully designed and controlled clinical trials that consider the probiotic(s), the host population and the study design.

Meta-analyses of probiotic trials collate data from multiple studies. These are a powerful statistical analysis tool in many fields of research as they can resolve uncertainty from conflicting results.20 However, this research approach is inappropriate for analysing the health benefits of probiotics if these benefits are species and strain-specific. The term ‘probiotics’ can be a label for a range of different microbial species. The majority of probiotics are gram-positive bacteria, in particular, Lactobacillusspecies.21 There are also gram-negative probiotics available such as Escherichia coli Nissle 191722 and yeasts such as Saccharomyces boulardii.23 The physiological structures of these organisms are different and interact with the human body in distinctive ways.24 Even different strains of the same species can secrete a variety of molecules stimulating a unique response in the host. A meta-analysis study of probiotics for the treatment of IBS pooled studies totaling 20 different strains of bacteria.25 Conclusions from this study could only suggest that probiotic use may be associated with improvement in IBS symptoms, but noted these results should be interpreted with caution due to the variability of trial designs of the included studies.25 Strain-specific benefits cannot be seen when meta-analysis treats all probiotic strains as identical.

Another meta-analysis study, published in 2016, investigated the effect of probiotic supplementation on the faecal microbiota in healthy participants by pooling results from seven randomised control trials. The authors concluded probiotic consumption had no effect on faecal microbiota composition.26 However, the interpretation of this result failed to acknowledge that probiotics do not necessarily need to colonise and have a persistent presence in the gut to offer a health benefit, especially in healthy individuals. For example, transient microbial populations can still stimulate the immune system.27 The meta-analysis highlighted the importance of defining the primary and secondary outcomes in research.26 It may have been more appropriate for faecal composition to be considered as a secondary outcome, and the primary outcome stimulation of immune responses.

The majority of experimental research into the health benefits of probiotics has been conducted on groups of diseased subjects, measuring the effect of the probiotic on disease-related symptoms. These studies are often designed purely for methodological reasons, as significant positive results are easy to identify. Studies of the benefits of probiotics for the healthy population are more complicated, as it is difficult to record significant positive physiological effects when functional abnormalities are not present.28 However, probiotics are principally marketed for use by healthy consumers. A limitation of the ability to measure positive immune effects in a healthy population is the difficulty in measuring significant differences where there is wide natural variation in, for example, immune parameters.

For the beneficial claims of probiotics to gain credibility in the clinical field, future clinical trials may need to be standardised. The only way various probiotic species can be compared is if they are tested in the same way, with primary and secondary outcomes well defined. There are hundreds of species and strains of probiotic bacteria that have not yet been thoroughly researched, but which need to be analysed independently to determine strain specific effects.

An important consideration in trial design is the calculation of the appropriate cohort size in order to obtain sufficient power to detect significance. A limiting factor of this may be that large cohort sizes are required when studying populations with high natural variability. Once the cohort size has been determined and an effective probiotic dose has been established, the test parameters that could be set include the dosing regime (for example, consistent consumption of probiotics for two weeks) and format of delivery (for example as a pill, in milk, yoghurt, as a liquid). Studies should aim to collect multiple faecal samples to indicate viability or colonisation of the probiotic and blood samples to measure systemic immune responses, as well as recording health scores and incidence of sickness. Analysis and outcomes that are reported in a consistent format would allow comparisons across multiple studies. The probiotic benefits should be tested on both healthy and diseased state participants. A problem with investigating probiotic effects on target diseases, such as IBS, is that these diseases are heterogeneous and therefore difficult to categorise. Analysis of probiotics in a standardised way would enable development of a data bank containing effects of all probiotic strains and species and make interpretation of health benefits more straightforward for health professionals and consumers.

Regulation of probiotics

Probiotics are part of a global health supplement industry. Guidelines, regulations and categorisation of probiotics vary from country to country. In New Zealand, probiotics can be sold as a ‘functional food’, a product that serves a physiological role beyond the provision of simple nutrient requirements.29 In the US, probiotics can be sold in a range of categories including dietary supplementation or probiotic drug. If a probiotic is sold as a drug, then it must first undergo the regulatory processes as a drug, and evidence must be supplied for the claimed health benefits. If a probiotic is sold as a dietary supplement, it comes under the umbrella of ‘food’ and does not require FDA approval, which is typical for bacterial genera with a history of use such as Lactobacillus species.30 Next-generation probiotics contain bacteria (such as Akkermansia species) that are not necessarily ubiquitous in food and do not have a history of probiotic use. These products are therefore difficult to both categorise and regulate. As more research of the healthy microbiome is published, new candidate probiotics will also need to be regulated in the absence of historical data. The category in which probiotics are sold determines the claims that can be made surrounding the health benefits. Manufacturers selling probiotics as functional foods can make generalised statements, for example “improves digestive health”. This statement suggests a benefit for probiotic consumption.31 Advertising like this is attractive to consumers and encourages sales.

In New Zealand, companies can base generalised health claims on one of the pre-approved food-health relationships set in Standard 1.2.7 by Food Safety Australia and New Zealand (FSANZ).32 Under this standard, health claims require supporting scientific evidence, but this can be self-substantiated by manufacturers. Companies must notify FSANZ when making a generalised health claim. FSANZ will then publish the health claim; however, they do not guarantee the accuracy of the information in the claim, or take responsibility for enforcing this requirement; their role is solely in public notification. Manufacturers can initiate trials of their own probiotic products, and benefits are marketed directly to consumers. As evidence is not easily accessible to the general public, consumers must trust products have been through the correct regulatory processes to make these claims. This can also cause healthcare professionals to doubt product efficacy and make it difficult to advise patients that enquire about probiotics.

In 2001, the World Health Organization Expert Consultation for the Evaluation of Health and Nutritional Properties of Probiotics developed a set of standardised guidelines for manufacturers to follow during the assessment of probiotic health benefits.30 This was an endeavor to increase integrity of health claims. The guidelines included identification of the genus and species of probiotic, determination of the mechanism of action of the probiotic effect via in vitro analysis; and the verification of probiotic health benefit by a human clinical trial.30 It was then the responsibility of the manufacturers to follow these guidelines and prove the efficacy, however only a few manufacturers followed those guidelines in published literature.

Healthcare professionals and consumers need to be able to assess scientific information to make informed decisions when using probiotics. To address this issue, we would benefit from an online resource which collates and translates the scientific literature on probiotics available in New Zealand into practical, easy to understand clinically relevant information. Such tools have already been created in Canada and the US, for example, the AEProbio Clinical Guide to Probiotic Products.33 In the meantime, consumers and health professionals rely on labelling of probiotic products to facilitate decision making. Interpreting variable labels is difficult; the recommended minimum information is shown in Figure 1.

Figure 1: An example of appropriate labelling on a probiotic product, and guide to interpreting the information.

c

Conclusions

Probiotics contain a variety of bacterial species, and consumers have a diverse gut microbial population that affects their health, and health benefits from probiotics are species- and strain-specific. Personalised probiotics for each individual are a distinct possibility in the future. Standardisation of clinical trial design and reporting would enable the health benefits from probiotic trials to be compared. Healthcare professionals and consumers in New Zealand need accessible, scientifically valid information on the probiotics available here and the ability to interpret product labelling in order to make informed decisions.

Summary

Abstract

Research into the health benefits of probiotics has growing interest. Reported benefits of probiotic consumption range from the improvement of intestinal function to immune support. However, trials of probiotics lack the standardisation required to judge efficacy. It is important to acknowledge that probiotic products include a range of bacterial species and strains that can have varied effects. In this article, we address the importance of correctly interpreting trials of proposed probiotics. We discuss the necessity to treat probiotic bacterial strains independently, and to communicate findings consistently through both data reporting and product labelling. Finally, we propose a new approach to study the health effects of probiotics in the future.

Aim

Method

Results

Conclusion

Author Information

Gemma Laws, MSc Candidate, Department of Microbiology and Immunology, University of Otago, Dunedin; Roslyn Kemp, Associate Professor, Department of Microbiology and Immunology, University of Otago, Dunedin.

Acknowledgements

Correspondence

Roslyn Kemp, Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin.

Correspondence Email

roslyn.kemp@otago.ac.nz

Competing Interests

GAL completed an MSc and was supported by Blis Technologies and Callaghan Innovation during her studies. This manuscript was prepared after submission of the thesis.

  1. Bull MJ, Plummer NT. Part 1: The human gut microbiome in health and disease. Integrative Medicine 2014; 13(6):17–22.
  2. Ozen M, Dinleyici EC. The history of probiotics: the untold story. Beneficial Microbes. 2015; 6(2):159–65.
  3. Ljungh A, Wadstrom T. Lactic acid bacteria as probiotics. Current Issues in Intestinal Microbiology. 2006; 7(2):73–89.
  4. Anderson RC, Cookson AL, McNabb WC, Park Z, McCann MJ, Kelly WJ, et al. Lactobacillus plantarum MB452 enhances the function of the intestinal barrier by increasing the expression levels of genes involved in tight junction formation. BMC Microbiology. 2010; 10(1):316.
  5. Todoriki K, Mukai T, Sato S, Toba T. Inhibition of adhesion of food-borne pathogens to Caco-2 cells by Lactobacillus strains. Journal of Applied Microbiology. 2001; 91(1):154–9.
  6. Sheu B-S, Cheng H-C, Kao A-W, Wang S-T, Yang Y-J, Yang H-B, et al. Pretreatment with Lactobacillus- and Bifidobacterium-containing yogurt can improve the efficacy of quadruple therapy in eradicating residual Helicobacter pylori infection after failed triple therapy. The American Journal of Clinical Nutrition. 2006; 83(4):864–9.
  7. Sartor RB. Mechanisms of Disease: pathogenesis of Crohn’s disease and ulcerative colitis. Nature Clinical Practice Gastroenterology & Hepatology. 2006; 3:390.
  8. Ashraf R, Shah NP. Immune system stimulation by probiotic microorganisms. Critical Reviews in Food Science and Nutrition. 2014; 54(7):938–56.
  9. Madsen KL, Doyle JS, Jewell LD, Tavernini MM, Fedorak RN. Lactobacillus species prevents colitis in interleukin 10 gene–deficient mice. Gastroenterology. 1999; 116(5):1107–14.
  10. Leyer GJ, Li S, Mubasher ME, Reifer C, Ouwehand AC. Probiotic effects on cold and influenza-like symptom incidence and duration in children. Pediatrics. 2009; 124(2):e172–e9.
  11. de Vrese M, Winkler P, Rautenberg P, Harder T, Noah C, Laue C, et al. Probiotic bacteria reduced duration and severity but not the incidence of common cold episodes in a double blind, randomized, controlled trial. Vaccine. 2006; 24(44):6670–4.
  12. Berggren A, Lazou Ahren I, Larsson N, Onning G. Randomised, double-blind and placebo-controlled study using new probiotic lactobacilli for strengthening the body immune defence against viral infections. European Journal of Nutrition. 2011; 50(3):203–10.
  13. Hammer GE, Turer EE, Taylor KE, Fang CJ, Advincula R, Oshima S, et al. Expression of A20 by dendritic cells preserves immune homeostasis and prevents colitis and spondyloarthritis. Nature Immunology. 2011; 12(12):1184–93.
  14. Takeda K, Suzuki T, Shimada S-I, Shida K, Nanno M, Okumura K. Interleukin-12 is involved in the enhancement of human natural killer cell activity by Lactobacillus casei Shirota. Clinical & Experimental Immunology. 2006; 146(1):109–15.
  15. Bourdeau T, Spertini F, Raymond F, Audran R, Gosoniu L, Mercenier A, et al. Transcriptomic analysis of PBMCs from allergic patients after probiotic treatment. Austin Journal of Nutrition and Metabolism. 2017; 4(1).
  16. Caballero-Franco C, Keller K, De Simone C, Chadee K. The VSL#3 probiotic formula induces mucin gene expression and secretion in colonic epithelial cells. American Journal of Physiology-Gastrointestinal and Liver Physiology. 2007; 292(1):G315–G22.
  17. Maneerat S, Lehtinen MJ, Childs CE, Forssten SD, Alhoniemi E, Tiphaine M, et al. Consumption of Bifidobacterium lactis Bi-07 by healthy elderly adults enhances phagocytic activity of monocytes and granulocytes. Journal of Nutritional Science. 2014; 2:e44.
  18. Ducrotté P, Sawant P, Jayanthi V. Clinical trial: Lactobacillus plantarum 299v (DSM 9843) improves symptoms of irritable bowel syndrome. World Journal of Gastroenterology. 2012; 18(30):4012–8.
  19. Kechagia M, Basoulis D, Konstantopoulou S, Dimitriadi D, Gyftopoulou K, Skarmoutsou N, et al. Health benefits of probiotics: A Review. ISRN Nutrition. 2013; 2013:481651.
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