Six trials administered multistrain probiotics, and 4 trials administered single-strain probiotics, primarily from the Lactobacillus and/or Bifidobacterium genera. The intervention duration ranged from 8 to 24 weeks.

Compared to a placebo, supplementation with probiotics had no effect on overall cognition or cognitive domains (including language, naming, visuospatial skills, memory, and attention). There was considerable heterogeneity in all of the analyses.

All of the trials were of good methodological quality.

Probiotics have no effect on cognition in adults with cognitive impairment Original paper