Effectiveness of probiotic supplementation in managing depressive symptoms and inflammatory status in patients with depression: A systematic review and meta-analysis

BACKGROUND AND AIMS: Depression is a multifactorial disorder influenced by genetic, biochemical, psychological, and environmental factors, and it significantly impacts quality of life. Probiotics, especially Lactobacillus and Bifidobacterium strains, have been proposed as adjunct therapies due to their capacity to modulate gut microbiota and the gut-brain axis. This systematic review and meta-analysis aimed to evaluate the effectiveness of probiotic supplementation on depressive symptoms and inflammatory status in individuals with depression. METHODS: Articles were identified through searches in databases including PubMed, Scopus, CINAHL, and Zenodo, using terms related to depression, microbiome, and probiotics. The search, conducted between January and February 2025, yielded 780 articles. After removing duplicates and applying eligibility criteria, 13 studies were included in the systematic review and 7 in the meta-analysis. RESULTS: Probiotic supplementation was significantly associated with improvement in depressive symptoms (p < 0.00001). However, no significant changes were found in inflammatory biomarkers, including interleukin-6 (p = 0.45) and tumor necrosis factor-alpha (p = 0.21). CONCLUSIONS: These results suggest that probiotics may help alleviate depressive symptoms, although their effect on inflammation remains uncertain. Further high-quality studies are necessary to clarify underlying mechanisms and determine the clinical relevance of probiotics as adjunctive therapy in depression..