Effect of probiotics on cognitive function in adults with mild cognitive impairment or Alzheimer's disease: A meta-analysis of randomized controlled trials

Background Recent clinical studies have yielded controversial results regarding the effect of probiotics on cognitive function in Alzheimer's disease (AD) or mild cognitive impairment (MCI) subjects. To clarify the efficacy of probiotics on cognition, we conducted a meta-analysis of randomized controlled trials (RCTs). Methods Instructions of the PRISMA 2020 statement were followed. Literature from the PubMed, Embase and Cochrane databases were systematically searched and manually screened for relevant published RCTs. We performed statistical analysis using RevMan, and assessed the risk of bias using the R software. Results A total of 12 studies comprising 852 patients with MCI or AD were identified. The results of meta-analysis showed that probiotics improved global cognitive function (SMD=0.67; 95% CI, 0.32, 1.02), recall/delayed memory (SMD=0.67; 95% CI: 0.32, 1.02), attention (SMD=0.31; 95% CI: 0.04, 0.58) and visuospatial/constructional (SMD=0.24; 95% CI: 0.06, 0.42) cognitive domain. Conclusion This meta-analysis found that probiotic supplementation is associated with an improvement in cognitive performance among patients with AD and MCI. However, current evidence is limited, and more reliable large-scale RCTs with higher methodological quality are needed.