Systematic review of probiotic supplementation in Alzheimer’s patients with results on cognitive function, health biomarkers, and microbiota

Background: Alzheimer’s disease (AD) is a prevalent neurodegenerative disorder in older adults, and growing evidence suggests that alterations in the gut-brain axis may contribute to its pathophysiology. Probiotics have been proposed as a potential adjunctive strategy to modulate gut microbiota and related systemic pathways; however, clinical evidence in AD remains limited and heterogeneous. This systematic review evaluated current evidence on the effects of probiotic supplementation on cognitive outcomes and health-related biomarkers in patients with AD. Methods: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, PubMed, Web of Science, and Scopus were systematically searched for double-blind randomized controlled trials published within the last 10 years (up to November 30, 2025). Studies assessing probiotic supplementation in clinically diagnosed AD patients were included. Methodological quality and risk of bias were evaluated using the Physiotherapy Evidence Database (PEDro) scale, the McMaster assessment tool, and the Cochrane Risk of Bias 2.0 tool. Results: Of 253 records identified, five randomized controlled trials met the inclusion criteria, comprising 328 participants. The studies evaluated different probiotic formulations, mainly involving Lactobacillus and Bifidobacterium species, administered over short-term interventions (12 weeks). Some trials reported statistically significant improvements in selected cognitive outcomes, inflammatory and oxidative stress markers, metabolic parameters, brain-derived neurotrophic factor levels, anxiety, and instrumental activities of daily living. However, results were heterogeneous and several outcomes were non-significant. No serious adverse events related to probiotic supplementation were reported. Discussion: Probiotic supplementation may be associated with strain-specific and short-term effects on selected cognitive and biological outcomes in patients with AD. Nevertheless, limited trial numbers, small sample sizes, and substantial heterogeneity preclude definitive conclusions. Further well-designed randomized controlled trials with standardized probiotic formulations and longer follow-up periods are required.