Effects of probiotic supplementation on depression, anxiety, and sleep quality in healthy participants: A systematic review and meta-analysis

This systematic review and meta-analysis evaluated the effects of probiotic supplementation on depression, anxiety, and sleep quality in healthy adults. PubMed, Cochrane Library, Web of Science, and Embase were searched from inception to September 18, 2026. Randomized controlled trials (RCTs) comparing probiotics with placebo for ≥4 weeks were included. Data from 20 studies involving 1,508 participants were analyzed using Stata 17.0. Random-effects or fixed-effects models were selected according to heterogeneity. The GRADE approach was used to assess evidence certainty. Probiotics significantly reduced depression scores (SMD = -0.23, 95% CI: -0.36 to -0.10, P < 0.01; I² = 4.67%) and improved sleep quality (SMD = -0.37, 95% CI: -0.52 to -0.22, P < 0.01; I² = 41.67%). However, the overall effect on anxiety was not significant (SMD = -0.11, 95% CI: -0.31 to 0.09, P = 0.27; I² = 61.41%). Subgroup analyses were exploratory and unadjusted; no definitive conclusion can be drawn regarding intervention duration or strain type. GRADE certainty was moderate for depression and sleep quality, but very low for anxiety. In conclusion, probiotic supplementation may alleviate depressive symptoms and improve sleep quality in healthy adults, whereas its effect on anxiety remains inconclusive. Larger, standardized RCTs are needed to confirm these findings and clarify strain-specific effects.