Efficacy of probiotics on anxiety—A meta‐analysis of randomized controlled trials

BACKGROUND: The concept "psychobiotics" claims potential beneficial effect of probiotics on anxiety, whereas findings from clinical trials are inconsistent. Thus, a meta-analysis is needed to clarify the effect of probiotics on anxiety. METHODS: Randomized controlled trials (RCTs) assessing the effect of probiotics on anxiety were systematically retrieved from online databases and manually screened for references of relevant published literature through September 1, 2017. Standardized mean difference in change from baseline of anxiety rating scales between probiotics groups and placebo groups was selected as the main effect index. Subgroup analyses were conducted with respect to overall health status of the sample, existence of gastrointestinal symptoms, strains of flora, trial duration, and risk of bias assessment. Publication bias was evaluated by funnel plot and Egger's test. The reliability of the result was assessed by leave-one-out sensitivity analysis. RESULTS: Twelve studies with 1,551 subjects (871 in probiotics group and 680 in control group) were included. All the studies were rated as low or moderate risk of bias. The meta-analysis and subgroup analyses all showed no significant difference between probiotics and placebo in alleviating anxiety symptoms. The Egger's test revealed no evidence of significant publication bias. Sensitivity analysis showed that leaving out one study would result in marginal significance. CONCLUSIONS: The evidence for the efficacy of probiotics in alleviating anxiety, as presented in currently published RCTs, is insufficient. More reliable evidence from clinical trials is needed before a case can be made for promoting the use of probiotics for alleviating anxiety.