The Neuropsychological Impact of Insulin Levels: Roles of Insulin in Parkinson's Disease and Cognitive Functioning

Abstract

Numerous studies demonstrate a relationship between insulin and Alzheimer's disease; however, little research exists on insulin's association to Parkinson's disease (PD) and Parkinson's disease dementia (PDD). The current study examined the connection between insulin and cognitive functioning in PD, PDD, and age-matched controls. A total of 22 older adult participants with PD completed the present study: 12 participants with PD (mean age = 67.50; 41.67% men; mean Mini Mental State Exam (MMSE) = 28.67) and 10 participants with PDD (mean age = 75.10; 90.00% men; mean MMSE = 22.90). Twenty-two non-demented older adults (mean age = 71.77; 63.64% men; mean MMSE = 29.23) from the University of Kansas Brain Aging Project served as the control group. Participants completed a neuropsychological assessment battery designed to represent cognitive domains of interest for individuals with PD and PDD as well as a two-hour glucose tolerance test. Total area under the curve (AUC) for blood insulin served as overall indices for insulin levels. PDD participants had lower absolute insulin values compared to PD participants and lower insulin levels were associated with decreased motor performance based on the Unified Parkinson's Disease Rating Scale (UPDRS) motor score. Contrary to predictions, higher insulin levels predicted poorer executive functioning performance for both PD and PDD participants. More research is needed to establish specific mechanisms to explain the relationship between higher insulin levels and reduced executive functioning performance. Additional research would also provide further evidence for insulin's role in cognitive changes for older adults with PD, PDD, and other neurodegenerative diseases.