Probiotics and Cognitive-Related Health Outcomes: An Umbrella Review of Systematic Reviews and Meta-Analyses of Randomized Controlled Trials

Context Numerous randomized controlled trial (RCT) meta-analyses have shown how beneficial probiotics are for a variety of health conditions. To date, to our knowledge, however, there has not been any synthesis of the overall strength and caliber of this evidence. Objective The objective is to evaluate the quality of evidence from published meta-analyses of RCTs that have examined the connections between probiotics and cognitive-related health outcomes. Data Sources The databases PubMed, Embase, Web of Science, Scopus, and Cochrane database of systematic reviews were searched from their respective starting dates until April 20, 2024. Included in the study were meta-analyses of RCTs that examined the effects of probiotics in adults. Data Extraction The meta-analysis extracted standardized mean differences, mean differences, 95% CIs, P values, and I2 statistics for each probiotic-related outcome. The effect sizes were recalibrated. We evaluated the evidence quality for each association using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) criteria and categorized it as high, moderate, low, or very low. Data Analysis A total of 17 meta-analyses included 156 RCTs (n = 51 unique RCTs) with sample sizes ranging from 37 to 409 and follow-up periods ranging from 0.5 to 28 weeks. A total of 106 unique associations were identified among various health outcomes. The median number of studies per association was 3, ranging from 2 to 14. Using the GRADE framework, among the 106 evaluated associations, 47 (44.3%) were nominally statistically significant (P < .05). Specifically, 18 associations (38.3%) demonstrated high evidence levels, 18 (38.3%) moderate, 10 (21.3%) low, and 1 (2.1%) very low. Among these significant associations, 21 (44.7%) concerned cognitive function, 3 (6.4%) involved blood glucose outcomes, 7 (14.9%) addressed lipid profile outcomes, 10 (21.3%) focused on oxidative stress markers, 2 (4.3%) examined inflammatory markers, and 4 (8.5%) related to other indicators. Conclusions In this comprehensive review, we found that the beneficial associations between probiotics and cognitive health outcomes are supported by moderate- to high-quality evidence. However, additional clinical trials are needed to investigate the effects of different probiotic strains, doses, and intervention durations on clinical outcomes. Systematic Review Registration PROSPERO registration No. CRD42024537769.