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

Abstract

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 (n = 3351 with diabetes), met study inclusion criteria. Small to moderate effect sizes were obtained for five of six domains: motor function (3 studies, n = 2374; d = -0.36), executive function (12 studies, n = 1784; d = -0.33), processing speed (16 studies, n = 3076; d = -0.33), verbal memory (15 studies, n = 4,608; d = -0.28), and visual memory (6 studies, n = 1754; d = -0.26). Effect size was smallest for attention/concentration (14 studies, n = 23,143; d = -0.19). The following tests demonstrated the most notable performance decrements in diabetes samples: Grooved Pegboard (dominant hand) (d = -0.60), Rey Auditory Verbal Learning Test (immediate) (d = -0.40), Trails B (d = -0.39), Rey-Osterreith Complex Figure (delayed) (d = -0.38), Trails A (d = -0.34), and Stroop Part I (d = -0.28). 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.

Fig. 1

Forest plot depicting effect sizes for neuropsychological tests within the verbal memory domain. Shown are Cohen’s d effect sizes (95% CI) for each study reporting the test and the pooled Cohen’s d effect size (95% CI) for the neuropsychological test and domain. The dotted line represents the Cohen’s d pooled effect size for the verbal memory domain. The overall effect size for the verbal memory domain is −0.28 (−0.37, −0.19). A negative Cohen’s d effect size estimate reflects poorer cognitive performance among individuals with type 2 diabetes relative to the nondiabetic comparison group. CVLT = California Verbal Learning Test, RAVLT = Rey Auditory Verbal Learning Test, WMS = Wechsler Memory Scale.

Fig. 2

Forest plot depicting effect sizes for neuropsychological tests within the visual memory domain. Shown are Cohen’s d effect sizes (95% CI) for each study reporting the test and the pooled Cohen’s d effect size (95% CI) for the neuropsychological test and domain. The dotted line represents the Cohen’s d pooled effect size for the visual memory domain. A positive Cohen’s d effect size estimate reflects better cognitive performance among individuals with type 2 diabetes relative to the nondiabetic comparison group. The overall effect size for the visual memory domain is−0.26 (−0.38,−0.14). A negative Cohen’s d effect size estimate reflects poorer cognitive performance among individuals with type 2 diabetes relative to the nondiabetic comparison group. Rey-O = Rey-Osterrieth Complex Figure Test, WMS = Wechsler Memory Scale.

Fig. 3

Forest plot depicting effect sizes for neuropsychological tests within the attention/concentration domain. Shown are Cohen’s d effect sizes (95% CI) for each study reporting the test and the pooled Cohen’s d effect size (95% CI) for the neuropsychological test and domain. The dotted line represents the Cohen’s d pooled effect size for the attention/ concentration domain. The overall effect size for the attention/concentration domain is −0.19 (−0.26, −0.12). A negative Cohen’s d effect size estimate reflects poorer cognitive performance among individuals with type 2 diabetes relative to the nondiabetic comparison group. WAIS = Wechsler Adult Intelligence Scale; WMS = Wechsler Memory Scale.

Fig. 4

Forest plot depicting effect sizes for neuropsychological tests within the processing speed domain. Shown are Cohen’s d effect sizes (95% CI) for each study reporting the test and the pooled Cohen’s d effect size (95% CI) for the neuropsychological test and domain. The dotted line represents the Cohen’s d pooled effect size for the processing speed domain. The overall effect size for the processing speed domain is−0.33 (−0.41,−0.26). A negative Cohen’s d effect size estimate reflects poorer cognitive performance among individuals with type 2 diabetes relative to the nondiabetic comparison group. WAIS = Wechsler Adult Intelligence Scale.

Fig. 5

Forest plot depicting effect sizes for neuropsychological tests within the executive function domain. Shown are Cohen’s d effect sizes (95% CI) for each study reporting the test and the pooled Cohen’s d effect size (95% CI) for the neuropsychological test and domain. The dotted line represents the Cohen’s d pooled effect size for the executive function domain. The overall effect size for the executive function domain is −0.33 (−0.42, −0.24). A negative Cohen’s d.

Fig. 6

Forest plot depicting effect sizes for neuropsychological tests within the motor function domain. Shown are Cohen’s d effect sizes (95% CI) for each study reporting the test and the pooled Cohen’s d effect size (95% CI) for the neuropsychological test and domain. The dotted line represents the Cohen’s d pooled effect size for the motor function domain. The overall effect size for the motor function domain is −0.36 (−0.52, −0.19). A negative Cohen’s d effect size estimate reflects poorer cognitive performance among individuals with type 2 diabetes relative to the nondiabetic comparison group.