A meta-analysis of the use of probiotics to alleviate depressive symptoms

Introduction: Some preclinical and clinical studies have demonstrated the positive impact of probiotic supplementation on depressive symptoms. This paper aims to provide an updated meta-analysis on the topic. Methods: Using the keywords [probiotics OR gut OR microflora OR microbiome OR bacteria OR yeast OR yoghurt OR lactobacillus OR bifidobacterium] AND [mood OR depression OR MDD OR suicide], a preliminary search on the PubMed, Ovid, Clinical Trials Register of the Cochrane Collaboration Depression, Anxiety and Neurosis Group (CCDANTR) and Cochrane Field for Complementary Medicine database yielded 917 papers published in English between 1-Jan-1960 and 1-June-2017. Results: 10 clinical trials with a total of 1349 patients were reviewed, comparing the use of probiotics to placebo controls. There was no significant difference in mood between the treatment and placebo group post-intervention as the standardized mean difference (SMD) was -0.128 (95% CI -0.261 to 0.00463, P=0.059). A separate subgroup analysis of studies conducted in healthy versus depressed individuals found significant improvements in the moods of individuals with mild to moderate depressive symptoms (SMD -0.684, 95% CI -1.296 to -0.0712, P=0.029) and non-significant effects in healthy individuals (SMD -0.0999, 95% CI -0.235 to 0.0348, P=0.146). Limitations: Inter-study discrepancies with respect to probiotic dosing, bacterial strains and strain combinations limit the comparability of current clinical trials. Furthermore, majority of existing RCTs were conducted in healthy individuals, making it difficult to extrapolate the results to depressed individuals. Conclusion: Probiotic supplementation has an overall insignificant effect on mood. Future studies should be conducted on more patients with clinically diagnosed depression.