Effect of Probiotic Supplementation on Cognitive Function and Metabolic Status in Mild Cognitive Impairment and Alzheimer's Disease: A Meta-Analysis

Background: Alzheimer's disease (AD) is a progressive and multifactorial neurodegenerative disease accounting for 80% of dementia worldwide.Objective: To assess the influence of probiotics on cognitive function in patients with mild cognitive impairment (MCI) and AD.Methods: PubMed, Embase, and Cochrane Library databases were searched for relevant studies.Results: Six randomized controlled trials involving 462 patients with MCI and AD were included in this meta-analysis. The probiotic administration had favorable effects on homeostasis model assessment-insulin resistance [HOMA-IR; Weighted mean difference (WMD) = -0.34, 95% confidence intervals (95% CI): -0.44 to 0.24, P < 0.001, I-2 = 0%], very low-density lipoprotein levels (VLDL; WMD = -3.71, 95% CI: -6.11 to -1.32, P=0.002, I-2 = 57.7%), quantitative insulin sensitivity check index (QUICKI; WMD = 0.01, 95% CI: 0.00-0.01, P = 0.003, I-2 = 51%), and triglyceride levels (WMD = -15.65, 95% CI: -27.48 to -3.83, P = 0.009, I-2 = 63.4%) in patients with AD. However, after Hartung-Knapp adjustment, all effects were non-significant except for HOMA-IR (MD = -0.34, 95%CI = -0.58 to -0.11). The changes in the Mini-Mental State Examination, repeatable battery for the assessment of neuropsychological status, and other biomarkers of oxidative stress, inflammation, and lipid profiles (high-sensitivity C-reactive protein, malondialdehyde, and total cholesterol) were negligible.Conclusion: The findings suggested that the consumption of probiotics had favorable effects on the HOMA-IR in patients with AD. However, the probiotic treatment did not affect cognitive function, other biomarkers of oxidative stress, and other lipid profiles.