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.