Probiotics for Mild Cognitive Impairment and Alzheimer’s Disease: A Systematic Review and Meta-Analysis

Study answer

What this study found

Probiotic and synbiotic supplementation improved cognitive function, with a significant effect in MCI and a modest effect in AD; overall results showed high heterogeneity; benefits were more pronounced with multiple strains, higher doses, longer duration, and earlier disease stage; therefore probiotics may improve cognitive function in MCI or AD, but evidence is insufficient and longer-term, large-scale trials are needed to confirm and optimize regimens.

Study & population

Eight randomized, double-blind, placebo-controlled trials in individuals with Alzheimer's disease (AD) or mild cognitive impairment (MCI); participants aged 50–90 years; total N = 174 AD and 446 MCI; studies conducted in Iran, Korea, Japan, USA, and Brazil.

Intervention

Daily probiotic (≥1×10^9 CFU) or synbiotic regimens for ~12 weeks (mostly 12 weeks; some 90 days or 16 weeks); delivery forms included encapsulated probiotics, probiotic-enriched pasteurized milk, and Kefir grain synbiotic; includes Lactobacillus rhamnosus GG, Lactobacillus spp., Bifidobacterium spp., and DW2009.

Key limitation

Some trials had small sample sizes; substantial heterogeneity across included studies due to differences in strains, dosages, durations, and disease stage; varied cognitive outcome measures; inconsistent diagnostic criteria; potential confounding from concurrent lifestyle/diet; incomplete reporting of adverse events;…

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Original abstract