Magnitude of cognitive dysfunction in adults with type 2 diabetes: a meta-analysis of six cognitive domains and the most frequently reported neuropsychological tests within domains

The objectives were to conduct a meta-analysis in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards to determine effect sizes (Cohen’s d) for cognitive dysfunction in adults with type 2 diabetes, relative to nondiabetic controls, and to obtain effect sizes for the most commonly reported neuropsychological tests within domains. Twenty-four studies, totaling 26,137 patients (n53351 with diabetes), met study inclusion criteria. Small to moderate effect sizes were obtained for five of six domains: motor function (3 studies, n52374; d520.36), executive function (12 studies, n51784; d520.33), processing speed (16 studies, n53076; d520.33), verbal memory (15 studies, n54,608; d520.28), and visual memory (6 studies, n51754; d520.26). Effect size was smallest for attention/concentration (14 studies, n523,143; d520.19). The following tests demonstrated the most notable performance decrements in diabetes samples: Grooved Pegboard (dominant hand) (d520.60), Rey Auditory Verbal Learning Test (immediate) (d520.40), Trails B (d520.39), Rey-Osterreith Complex Figure (delayed) (d520.38), Trails A (d520.34), and Stroop Part I (d520.28). This study provides effect sizes to power future epidemiological and clinical diabetes research studies examining cognitive function and to help inform the selection of neuropsychological tests