Probiotics for Mild Cognitive Impairment and Alzheimer’s Disease: A Systematic Review and Meta-Analysis
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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Open PDFOriginal abstract
Accumulating evidence from animal studies supports the potential role of probiotics and prebiotics in alleviating neurodegenerative diseases. However, whether dietary supplementation with probiotics improves cognitive function in patients with Alzheimer’s disease (AD) or mild cognitive impairment (MCI) is unclear. We searched literature databases for relevant randomized control trials and compared the outcomes between control/placebo and intervention groups. The results of the included studies were meta-analyzed using a random-effects model, with standardized mean differences (SMDs) and 95% confidence intervals (CIs) calculated as summary statistics. We also performed a risk-of-bias assessment, sensitivity analysis and subgroup analysis. Among the 294 articles identified, eight articles involving 174 patients with AD and 446 with MCI were included in the qualitative synthesis and seven studies were meta-analyzed. Our analysis detected high between-group heterogeneity (SMD = 0.43, 95% CI −0.02–0.88, p < 0.0001, I2 = 86.4%) in cognitive function across the included studies. Subgroup analyses identified a significant effect of probiotics on cognitive function only in the studies involving people with MCI (I2 = 44%, p = 0.15 for heterogeneity, p = 0.0002 for overall effect). Our findings suggest that dietary supplementation with probiotics improves cognitive function, especially in people with MCI.