title: Probiotics and Subclinical Psychological Symptoms in Healthy Participants: A Systematic Review and Meta-Analysis.
abstract: OBJECTIVE
  Interest in the gut-brain axis and emerging evidence that the intestinal microbiota can influence central nervous system function has led to the hypothesis that probiotic supplementation can have a positive effect on mood and psychological symptoms such as depression and anxiety. Although several human clinical trials have investigated this, results have been inconsistent. Therefore, a systematic review and meta-analytic approach was chosen to examine if probiotic consumption has an effect on psychological symptoms.
  
  
  METHODS
  The online databases PubMed, Scopus, and the Cochrane Library were searched for relevant studies up to July 2016. Those that were randomized and placebo controlled and measured preclinical psychological symptoms of depression, anxiety, and perceived stress in healthy volunteers pre and post supplementation with a probiotic were included. To control for differences in scales of measurement, data were converted to percentage change, and the standardized mean difference between the probiotic and control groups was investigated using Revman software. A random effects model was used for analysis. Heterogeneity was assessed using the I2statistic. Quality assessment was undertaken using the Rosendal scale.
  
  
  RESULTS
  Seven studies met the inclusion criteria and provided data for nine comparisons. All studies passed the quality analysis. The meta-analysis showed that supplementation with probiotics resulted in a statistically significant improvement in psychological symptoms (standardized mean difference 0.34; 95% confidence interval 0.07-0.61, Z = 2.49) compared with placebo.
  
  
  CONCLUSIONS
  These results show that probiotic consumption may have a positive effect on psychological symptoms of depression, anxiety, and perceived stress in healthy human volunteers.
authors.affiliation: 1 School of Medical Science, Griffith University , Gold Coast, Australia .
authors.forename: Jennifer
authors.initials: J
authors.lastname: McKean
authors.affiliation: 1 School of Medical Science, Griffith University , Gold Coast, Australia .|2 Menzies Health Institute , Gold Coast, Australia .
authors.forename: Helen
authors.initials: H
authors.lastname: Naug
authors.affiliation: 1 School of Medical Science, Griffith University , Gold Coast, Australia .|2 Menzies Health Institute , Gold Coast, Australia .
authors.forename: Elham
authors.initials: E
authors.lastname: Nikbakht
authors.affiliation: 1 School of Medical Science, Griffith University , Gold Coast, Australia .|2 Menzies Health Institute , Gold Coast, Australia .
authors.forename: Bianca
authors.initials: B
authors.lastname: Amiet
authors.affiliation: 1 School of Medical Science, Griffith University , Gold Coast, Australia .|2 Menzies Health Institute , Gold Coast, Australia .
authors.forename: Natalie
authors.initials: N
authors.lastname: Colson
mesh_terms: D000339:Affect; D001007:Anxiety / Q000188:drug therapy; D035843:Biomedical Research; D003863:Depression / Q000188:drug therapy; D000069196:Gastrointestinal Microbiome; D064368:Healthy Volunteers / Q000523:psychology* / Q000706:statistics & numerical data*; D006801:Humans; D009752:Nutritional Status; D019936:Probiotics / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D016896:Treatment Outcome
keywords: meta-analysis; neuropsychology; nutrition; probiotics