25-hydroxyvitamin D Levels are Associated with Cognitive Dysfunction in Type 2 Diabetes and the Metabolic Syndrome: A Preliminary Examination

Abstract

Background: Type 2 diabetes (T2DM) and metabolic syndrome are linked to pathological changes in the brain and increased likelihood of cognitive impairment. Vitamin D insufficiency is commonly found in this population and is associated with cognitive dysfunction in other patient groups. The present study aims to demonstrate the presence of cognitive deficit in individuals with T2DM and metabolic syndrome, and determine if level of vitamin D is associated with cognitive deficit in this population. Methods: Twenty individuals with T2DM and metabolic syndrome (n = 20, aged 45 to 72) were recruited for this cross-sectional study from a subspecialty diabetes center. All completed computerized cognitive testing and clinical evaluation, including assessment of circulating vitamin D values. Pearson correlations determined the association between vitamin D value and test performance. Results: Cognitive dysfunction was prevalent, particularly in domains of executive function (e.g., Verbal Interference-Color Word, 47%) and attention (e.g., Working Memory Reaction Time, 50%; Digit Span, 30%). Lower vitamin D values were associated with poorer executive function test performance (Switching of Attention-Letters/Numbers, r = 0.64; Maze Errors, r = 0.47). Conclusions: Cognitive dysfunction was prevalent, and lower vitamin D values were associated with poorer executive function test performance. It is unclear if vitamin D directly affects cognition in this population, or if it serves as a proxy for another mechanism affecting cognition, such as poorer glycemic control or sedentary lifestyle. Prospective studies involving vitamin D supplementation may be of benefit in addressing the possible causal role of vitamin D in cognition for this population.