Cognitive impairment, ranging from mild cognitive impairment to dementia, is increasingly recognized as a potential complication of diabetes. The increase in the prevalence of diabetes along with the aging of the population may result in a large increase in the prevalence of cognitive impairment in persons with diabetes. Approximately one-third of the United States adult population has prediabetes or diabetes. However, about one-half of persons age ≥60 years, who are most at risk for cognitive impairment, have prediabetes or diabetes. The association of diabetes and cognitive impairment may reflect a direct effect on the brain of hyperglycemia or the effects of the diabetes-associated comorbidities, such as hypertension, dyslipidemia, or hyperinsulinemia. There is evidence for an effect of diabetes-related processes on both neurodegenerative and vascular processes, thus contributing to both Alzheimer’s-like cognitive impairment, i.e., amnestic, and cerebrovascular-type cognitive impairment characterized by impairment in executive cognitive function.
This chapter reviews epidemiologic studies of the association between diabetes and cognitive impairment in large clinical or community-based studies, emphasizing studies in the United States. Type 1 diabetes is, in general, related to modest decrements in cognitive abilities, primarily in executive-frontal abilities. Type 2 diabetes seems to be more strongly related to vascular and non-amnestic forms of cognitive impairment, including non-amnestic mild cognitive impairment and vascular dementia, but it also seems to have a less strong association with amnestic forms of cognitive impairment, including amnestic mild cognitive impairment and Alzheimer’s dementia.
The relation of diabetes to cognitive impairment has therapeutic implications. There is conflicting evidence from clinical trials of diabetes interventions examining the effects of better glucose control on cognition and the brain. Lifestyle interventions among persons with diabetes and prediabetes do not seem to be related to better cognitive outcomes in the long term.
Despite many studies documenting the association between diabetes and cognitive impairment, the causal nature and the mechanisms of this association have not been fully established and require further study.