The effect of probiotics on select cognitive domains in mild cognitive impairment and Alzheimer's disease: A systematic review and meta-analysis

Background Mild cognitive impairment (MCI) and Alzheimer's disease (AD) are progressive neurodegenerative disorders, and probiotics may offer therapeutic benefits by modulating gut microbiota and reducing inflammation. Objective This study systematically evaluated the impact of probiotics on cognitive function in MCI and AD through a meta-analysis of randomized controlled trials (RCTs). Methods A systematic review and meta-analysis were performed following PRISMA 2020 guidelines. PubMed, Embase, EBSCO, and Cochrane databases were searched for RCTs (January 2000–January 2024) on probiotic interventions lasting 8–24 weeks. Cognitive outcomes included Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), language, naming, visual-spatial, memory, and attention. Data were analyzed using R with a random-effects model to calculate pooled standardized mean differences (SMDs) with 95% confidence intervals (CIs). Risk of bias was rigorously assessed. Results Out of 2000 articles, 500 full texts were screened, and 10 studies were included. The meta-analysis showed varied effect sizes: MMSE (SMD: 0.28, 95%CI −0.35–0.91, p = 0.38), MoCA (SMD: 0.51, 95%CI −0.49–1.52, p = 0.33), language (SMD: −0.12, 95% CI −0.54–0.29, p = 0.56), naming (SMD: 0.02, 95%CI −0.69–0.74, p = 0.95), visual-spatial (SMD: 0.38, 95%CI −0.13–0.88, p = 0.14), memory (SMD: 0.20, 95%CI −0.15–0.55, p = 0.26), and attention (SMD: −0.07, 95%CI −0.44–0.30, p = 0.71). Positive SMDs suggest cognitive improvement, while non-significant negative SMDs indicate trends toward decline, inclined by probiotic strains, duration, and participant characteristics. Conclusions Probiotics did not significantly improve cognitive function in MCI and AD patients, with variability in effects across cognitive domains, suggesting the need for tailored interventions and future studies.