1. According to a community-based study, diabetes during midlife was associated with increased rates of cognitive decline.
2. Patients with an increased duration of diabetes were associated with increased cognitive decline.
Evidence Rating Level: 2 (Good)
Study Rundown: There are approximately 20 million adults living in the US with diabetes. Previous research has shown an association between diabetes and dementia, but few large trials have investigated the nature of this relationship. In this study, middle-aged American adults were followed for 20 years following initial testing for diabetes and pre-diabetes. Cognitive decline was measured using standard tests of executive function, memory, language, and cognitive processing speed. Over 20 years, patients with diabetes and pre-diabetes had a greater extent of cognitive decline than patients without these conditions. Additionally, a longer duration of diabetes was associated with greater cognitive decline. Although this study used long-term data and a large sample size, its findings were limited by the relatively smaller percentage of black patients included, reducing its generalizability to the population at large. Furthermore, blood tests for diabetes were only conducted at a single baseline visit, meaning that the relationship between cognitive decline and subjects’ control of their blood sugars over time could not be evaluated.
In-Depth [prospective cohort]: This investigation employed data from the Atherosclerosis Risk in Communities study. Baseline glycated hemoglobin (HbA1c) values were collected for 13,351 black and white Americans, and three standardized tests of cognitive function—the delayed word recall test, a digit symbol substitution test, and the word fluency test—were used to assess cognitive function at baseline and after 20 years of follow-up. Global cognitive function scores were computed by averaging scores from these individual tests. Overall, patients with diabetes had increased cognitive decline (adjusted Z-score -0.15; 95% CI, -0.22 to -0.08) compared to those without diabetes after 20 years on the global function score, a difference that was approximately equivalent to 5 years of age. Poorly controlled diabetes (i.e., HbA1c ≥7.0%) was linked with greater cognitive decline, though this association was not significant (p=0.071). Longer duration of diabetes was associated with decreased cognitive scores (p<0.001), even after adjustment for potential cofounders, such as history of stroke. Overall, this study provides strong support for the association between diabetes and cognitive decline, and raises the possibility that improving glycemic control in mid-life may delay cognitive decline.
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