Probiotics and aging: Impacts on cognitive function, brain-derived neurotrophic factor, inflammation, and antioxidant activity. A systematic review and meta-analysis

Background Cognitive decline represents a major challenge in aging populations. Probiotics have been proposed to influence cognitive function through gut–brain interactions, but clinical findings remain inconsistent. Objective This study evaluated the effects of probiotic supplementation on cognitive function as the primary outcome, and on BDNF levels, inflammatory markers, and oxidative stress biomarkers as secondary outcomes in adults aged 50 years and older. Methods A systematic search of PubMed, EBSCO, ProQuest, and Google Scholar was conducted through 1 May 2024 using predefined search terms related to probiotics, cognitive function, BDNF, inflammation, and antioxidant activity. Study quality was assessed using the RoB 2 tool. Meta-analyses were performed using random-effects models, and publication bias was explored using Egger's test where study counts permitted. Results Sixteen studies demonstrated significant improvement in cognitive function among participants receiving probiotics compared to placebo. Cognitive function, measured using the Mini-Mental State Examination (MMSE), yielded a standardized mean difference (SMD) of 0.747 (95% CI 0.307–1.186) which corresponds to moderate-to-large effects. In comparison, the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) showed significant results with an SMD of 0.340 (95% CI 0.032–1.366) which corresponds to small-to-moderate effects. Probiotics also led to significant changes in several biochemical parameters, including BDNF, TNF-α, 8-OHdG, IL-6, IL-10, MDA, TAC, and GSH. Multi-strain probiotics showed better results compared to single-strain. Conclusions Probiotic supplementation may offer modest cognitive benefits in aging populations, particularly in studies enrolling cognitively impaired individuals, but substantial heterogeneity and limited biomarker evidence restrict the certainty of these findings. Larger, longer-duration, and standardized trials are needed to clarify the clinical relevance and potential biological pathways underlying probiotic effects on cognition.