Cognitive Decline and Dementia Risk in Type 2 Diabetes
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Liesel-Ann Meusel1, PhD, Ekaterina Tchistiakova2,3, BSc, William Yuen4,5, BSc, Bradley J Macintosh2,3, PhD, Nicole D Anderson1,6, PhD, and Carol E Greenwood4,5, PhD
1Rotman Research Institute, Baycrest Centre, Toronto, ON. 2HSF Centre for Stroke Recovery, Sunnybrook Research Institute, Toronto, ON. 3Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, ON.
4Kunin-Lunenfeld Applied and Evaluative Research Unit, Baycrest Centre, Toronto, ON. 5Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, ON. 6Departments of Psychology and Psychiatry, University of Toronto, Toronto, ON.
Abstract
Type 2 diabetes mellitus is increasingly common, and previously unrecognized complications are emerging; namely, cognitive impairment and dementia. The mechanisms that link these factors together are still unknown, but likely result from the interplay of several variables, including vascular change, poor glycemic control, inflammation, and hypothalamic pituitary adrenal overactivity. At present, it is still too early to propose best practices related to the management of diabetes-induced cognitive change. All things considered, however, patients should be aware that proper management of metabolic and vascular complications may minimize the adverse effects of type 2 diabetes on cognitive function and quality of life.
Keywords: type 2 diabetes, cognition, dementia, vascular, metabolic.
Type 2 diabetes mellitus is becoming increasingly common; over the next two decades, the number of adults diagnosed with diabetes in developed countries is expected to rise by 20% overall, and by 38% for those over 60 years of age.1 This rise in prevalence has been attributed to a sedentary lifestyle, obesity, and critically, to better health care, which has improved longevity for aging adults.
As a result of people living longer with diabetes, previously unrecognized complications are emerging; namely, cognitive impairment and dementia. Subtle cognitive deficits on tests of processing speed,2 working memory,3 declarative memory, attention, and executive function4 are evident even in middle-aged adults with type 2 diabetes. In addition, longitudinal studies show cognitive declines that significantly exceed the effects of normal aging.5 Beyond the age of 65 years, type 2 diabetes conveys the highest risk for progression to dementia: a 6-8% population attributable risk, over and above that of hypertension, dyslipidaemia, and obesity.6
The mechanisms that link type 2 diabetes to cognitive impairment and dementia are still unknown, however they are most likely multifactorial and result from the interplay of a range of variables, including macro- and microvascular changes, poor glycemic control, inflammatory mediators, rheological factors, and heightened hypothalamic pituitary adrenal (HPA) axis activity.7 This represents an expanded understanding of the impact of type 2 diabetes on brain health. The adverse effects of vascular dysfunction remain a concern; however, it is now acknowledged that other metabolic disturbances in type 2 diabetes are equally harmful.