Effect of probiotics on cognitive function and cardiovascular risk factors in mild cognitive impairment and Alzheimer's disease: an umbrella meta-analysis.

Background: This umbrella meta-analysis evaluates the effects of probiotics on cognitive function and metabolic health in Alzheimer's disease (AD) and mild cognitive impairment (MCI) by synthesizing findings from meta-analyses of randomized controlled trials (RCTs), as existing evidence remains inconclusive.

Methods: A systematic search was conducted in PubMed, Web of Science, and Scopus to identify meta-analyses of RCTs investigating the impact of probiotic supplementation on cognitive function and metabolic biomarkers. The random-effects model was used. Heterogeneity and publication bias were assessed.

Results: Thirteen meta-analyses, comprising 3910 patients, were included. Probiotics significantly improved cognitive function in AD (SMD = 0.78, 95% CI: 0.33 to 1.23) and MCI (SMD = 0.43, 95% CI: 0.15 to 0.70). Probiotics also increased total antioxidant capacity (SMD = 0.40, 95% CI: 0.11 to 0.70) and reduced MDA (SMD =  - 0.35, 95% CI: - 0.62 to - 0.09) and hs-CRP (SMD =  - 0.59, 95% CI: - 0.87 to - 0.30). Insulin resistance improved, as reflected by decreased HOMA-IR (SMD =  - 0.34, 95% CI: - 0.43 to - 0.26). No significant effects were observed on glutathione, nitric oxide, or lipid profiles.

Conclusion: Probiotic supplementation appears to enhance cognitive function and metabolic parameters in individuals with MCI and AD, likely through mechanisms involving inflammation reduction, oxidative stress modulation, and improved insulin sensitivity. Further high-quality RCTs are required to validate these findings and determine optimal probiotic formulations.