The anxiolytic effect of probiotics: A systematic review and meta-analysis of the clinical and preclinical literature

• Published in: PloS one Vol. 13; no. 6; p. e0199041
• Main Authors: Reis, Daniel J, Ilardi, Stephen S, Punt, Stephanie E W
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 20-06-2018; Public Library of Science (PLoS)
• Subjects: Animal behavior; Animal diseases; Animals; Anti-Anxiety Agents - therapeutic use; Antibiotics; Anxiety; Anxiety - drug therapy; Anxiety Disorders - drug therapy; Biology and Life Sciences; Cardiovascular disease; Care and treatment; Drug Evaluation, Preclinical; Exploratory Behavior - drug effects; Female; Humans; Inflammatory bowel disease; Irritable bowel syndrome; Lactobacillus rhamnosus; Male; Maze Learning - drug effects; Medicine and Health Sciences; Mental disorders; Meta-analysis; Metabolism; Mice; Microbiota; Microorganisms; Patient outcomes; Physical Sciences; Probiotics; Probiotics - pharmacology; Probiotics - therapeutic use; Psychology; Randomized Controlled Trials as Topic; Rats; Research and Analysis Methods; Research Design; Social Sciences; Species; Species Specificity; Studies; Subgroups; Systematic review; United States > US
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0199041

Probiotics have generated intensive research interest in recent years as a novel mode of treatment for physical and mental illness. Nevertheless, the anxiolytic potential of probiotics remains unclear. The present systematic review and meta-analysis aimed to evaluate the clinical and preclinical (animal model) evidence regarding the effect of probiotic administration on anxiety.
The PubMed, PsycINFO, and Web of Science databases were reviewed for preclinical and clinical studies that met the defined inclusion and exclusion criteria. The effects of probiotics on anxiety-like behavior and symptoms of anxiety were analyzed by meta-analyses. Separate subgroup analyses were conducted on diseased versus healthy animals, specific preclinical probiotic species, and clinical versus healthy human samples.
Data were extracted from 22 preclinical studies (743 animals) and 14 clinical studies (1527 individuals). Overall, probiotics reduced anxiety-like behavior in animals (Hedges' g = -0.47, 95% CI -0.77 --0.16, p = 0.004). Subgroup analyses revealed a significant reduction only among diseased animals. Probiotic species-level analyses identified only Lactobacillus (L.) rhamnosus as an anxiolytic species, but these analyses were broadly under-powered. Probiotics did not significantly reduce symptoms of anxiety in humans (Hedges' g = -0.12, 95% CI -0.29-0.05, p = 0.151), and did not differentially affect clinical and healthy human samples.
While preclinical (animal) studies suggest that probiotics may help reduce anxiety, such findings have not yet translated to clinical research in humans, perhaps due to the dearth of extant research with clinically anxious populations. Further investigation of probiotic treatment for clinically relevant anxiety is warranted, particularly with respect to the probiotic species L. rhamnosus.