Type 2 Diabetes and Cognitive Functions in Middle Age: A Meta-Analysis.

Objectives: Type 2 diabetes mellitus has been linked with cognitive decrement and an increased risk of dementia in older people. Less is known about whether diabetes affects cognition at younger ages. The objective of this meta-analysis was to examine possible differences (effect sizes) in cognitive performance between middle-aged type 2 diabetic patients and healthy controls. Secondary aim was to examine whether age is related to the magnitude of effect sizes. Methods: Electronic databases and lists of references of selected articles were used to search for studies examining type 2 diabetes and cognition in patients under age 65 compared to healthy controls. Twelve studies met the inclusion criteria. Standardized mean differences (Hedges's g) were calculated for main cognitive domains and their subdomains. Association between age and effect sizes was evaluated with meta-regression analyses. Publication bias and methodological quality of the studies were assessed. Results: Patients performed worse than controls in several cognitive functions. The largest differences were found in information processing speed (g = -0.68), attention/concentration (g = -0.55), executive functions (g = -0.51), and working memory (g = -0.51). There was no significance difference in visual memory (g = -0.15). Age was significantly related to the effect size in information processing speed, language, verbal memory and visual memory. However, the direction of association varied across these cognitive domains. Conclusions: The results suggest that cognitive decrement in diabetes is not restricted to older people, but may begin to appear in middle age. More attention should be paid to early recognition and treatment of diabetes-related cognitive decrement in healthcare systems. (JINS, 2019, 25, 215-229).