Link between diabetes and cognitive impairment

Abstract

Clinical experience and multiple research studies suggest that persons with diabetes are more likely to develop cognitive impairment or frank dementia, which may be Alzheimer’s type or vascular dementia. Initially, this may be subtle and manifest itself as mental slowing or apathy. On the other hand, patients with Alzheimer’s disease have an increased risk of developing type 2 diabetes. What both these groups have in common is advanced age, a genetic predisposition, and comparable pathological features in the pancreatic islets and the brain, namely amyloid derived from amyloid B protein in the brain of Alzheimer’s disease and islet amyloid derived from islet amyloid polypeptide in the pancreas in type 2 diabetes. A study of subjects from the Mayo Clinic Alzheimer Disease Patient Registry found that both Type 2 diabetes (35 percent vs. 18 percent; P<0.05) and impaired fasting glucose (46 percent vs. 24 percent; P<0.01) were more prevalent in Alzheimer’s disease vs. non-Alzheimer disease control subjects. Hence, 81 percent of cases of Alzheimer’s disease had either Type 2 diabetes or IFG. In selected subjects where autopsy data were available, isletcell amyloid was more frequent and extensive in patients with Alzheimer’s disease than the non-Alzheimer’s disease controls. However, diffuse neuritic plaques were not more common in patients with type 2 diabetes than in control subjects. The Honolulu-Asia Aging Study investigated the effects of brain aging in very old men of Japanese-American descent born between 1900 and 1919 utilizing MRI. The prevalence of diabetes in this cohort was 38 percent, and subjects with type 2 diabetes had a moderately increased risk of lacunes (small brain infarcts), (odds ratio (OR) 1.6), and atrophy of the hippocampus (OR 1.7). Those with a longer history of diabetes, those taking insulin, and those with complications had more common pathological changes commonly seen in dementia.