Spotlight on cognitive effects of diabetes

Two recent studies looked at the effects of diabetes on the brain, one focusing on mild cognitive impairment and the other on brain imaging findings.

The first study, published in the Journal of Diabetes and its Complications on April 19, included 202 patients with mild cognitive impairment (MCI). Half had type 2 diabetes and half were nondiabetic, and they were matched by age and gender. Over a mean follow-up of 28 months, 57.4% of the diabetes patients developed dementia, compared to 42.6% of the nondiabetic patients (P=0.02). Alzheimer's was the most common form of dementia (23%), followed by vascular dementia (14%). After adjustment, diabetes was found to be a risk factor for dementia (odds ratio, 2.09; 95% CI, 1.15 to 3.79), as was the APOE4 genotype. Patients who developed dementia were also more likely to have diabetic retinopathy.

The results show that type 2 diabetes is a risk factor for conversion to dementia from MCI, and both the APOE4 allele and diabetic retinopathy “might be contemplated as a herald of dementia risk in MCI patients,” the authors said. The study raises the question of whether diabetes patients should be screened for MCI, they added. Although an argument against this would be the lack of treatment for MCI, the authors support diagnosing impairment “because it would permit us to design specific patient-centered programs addressed to improve their treatment adherence and quality of life.”

The second study, published by Diabetologia on April 27, included 100 Korean patients with type 2 diabetes between ages 30 and 60 years with disease duration of less than five years. Half were overweight or obese (body mass index ≥25 kg/m2) and the other half were normal weight (body mass index <25 kg/m2). Fifty normal-weight patients without type 2 diabetes were also included as controls. Using brain imaging, the study found significantly lower global mean cortical thickness in the overweight/obese group than in the normal-weight diabetes group. The overweight/obese group also had negative correlations between disease duration and global mean white matter integrity and psychomotor speed performance, while the normal-weight diabetes patients showed neither.

The results reveal the presence of pronounced brain changes early in diabetes and suggest that weight status may play an additive role in diabetes-related brain and cognitive alterations, the study authors said. They noted that effects were primarily observed in the temporal lobe of the brain, which is also where the earliest changes associated with Alzheimer's disease are seen. “Our findings also highlight the need for early intervention aimed to reduce risk factors for overweight or obesity in type 2 diabetic individuals to preserve their brain structure and cognitive function,” the authors wrote. They noted that people of Asian ethnicity appear to be more prone to developing insulin resistance with slight increases in body mass index.