The role of probiotics in the improvement of cognitive performance of older adults: a meta-analysis.

With our increasing lifespan comes an increasing prevalence of age-related neurological diseases, which are often difficult to treat. The gut-brain axis may provide opportunities for cognitive health improvement through gut microbiota-targeting interventions, such as probiotics. The aim of this meta-analysis is to determine the clinical potential of probiotics for the amelioration of cognitive functioning in older adults. Systematic searches were executed in PubMed, Scopus, and Web of Science to retrieve published records of randomised controlled trials (RCTs). Records were assessed to fit the criteria of focusing on probiotic supplementation with cognitive functioning as the main outcome. After screening and assessment of 56 identified records, 20 RCTs were included for analysis. Reported means and standard deviations of cognitive test scores were used to calculate standardised mean differences (SMD) with a random effects model. Where applicable, blood concentrations of pro-inflammatory cytokines were taken as a secondary outcome. Based on the calculated SMDs it appears, overall, that supplementation of probiotics tends to have positive effects on both cognitive performance and reduction of inflammatory markers in older adults, albeit not significant (SMD [95%CI] = 0.19 [-0.13, 0.52] for cognitive performance, and SMD [95%CI] = -0.44 [-0.94, 0.06] for inflammation). The set of RCTs studied here is characterised by high heterogeneity, preventing the determination of a true overall effect size.