Strain-specific effects of probiotics on depression and anxiety: a meta-analysis.

Introduction: Depression and anxiety are pervasive mental health disorders with substantial global burdens. Probiotics, live microorganisms known for their health benefits, have emerged as a potential therapeutic intervention for these conditions. This systematic review and meta-analysis aim to evaluate the strain-specific effects of probiotics on relieving depressive and anxiety symptoms while elucidating underlying mechanisms.

Methods: EMBASE, Cochrane CENTRAL and PubMed/Medline were systematically queried to identify studies released until May 15, 2024. Randomized Controlled Trials (RCTs) that employed standardized assessment tools for depression and anxiety namely Beck Depression Inventory (BDI), Hamilton Depression Rating Scale (HAMD), Depression Anxiety Stress Scales (DASS), or Montgomery-Asberg Depression Rating Scale (MADRS) were included.

Results: 12 RCTs involving 707 participants were included. Seven RCTs utilizing the BDI questionnaire demonstrated a significant decrease in depressive symptoms favoring probiotics containing strains such as Lactobacillus acidophilus, Lactobacillus paracasei, Lactobacillus casei, Lactobacillus plantarum, Lactobacillus salivarius, Bifidobacterium bifidum, Bifidobacterium lactis, Bifidobacterium breve, and Bifidobacterium longum (MD: -2.69, CI95%: -4.22/-1.16, p value: 0.00). Conversely, RCTs using HAMD showed a non-significant reduction in depressive symptoms (MD: -1.40, CI95%: -3.29/0.48, p value: 0.14). RCTs employing DASS and MADRS scales also showed no significant differences.

Conclusion: This meta-analysis offers valuable insights into the strain-specific effects of probiotics containing Lactobacillus and Bifidobacterium species on depressive and anxiety symptoms. While our findings suggest a significant reduction in depressive symptoms based on the BDI scale favoring probiotics, the lack of significant effects observed on the HAMD, DASS, and MADRS scales underscores the complexity inherent in these conditions. It is imperative to acknowledge the mixed results across different measurement scales, indicating the need for cautious interpretation. Therefore, we advocate for a nuanced understanding of probiotics' impacts on various dimensions of mood, emphasizing the necessity for further research.