Abstract
Objectives
Peripheral insulin resistance (IR) and impaired glucose metabolism increases the risk for cognitive decline. However, data looking at peripheral IR's relationship with cognition in cognitively normal adults is limited. This study aimed to assess the relationship between peripheral IR and tests of speed of processing (SOP) in cognitively normal older adults using a novel IR measure.
Methods
Baseline data from 56 cognitively normal older adults participating in a nutrition intervention study (Nutrition Interventions for Cognitive Enhancement study; NICE study) were analyzed. Fasting blood draws were attained, and peripheral IR was measured using Quest Diagnostics’ Cardio IQ Insulin Resistance Panel (Test Code: 36,509). A cognitive battery was conducted by a trained psychometrician. Z-Scores of the Digit Symbol Substitution Test, Stroop Color, Stroop Word, Stroop Interference, and Stroop Letter Number Sequencing and Crossing-Off tests were combined to give a global SOP score. We constructed ordinary least squares regression models to assess IR's relationships with individual SOP tests and global SOP, including age and education as covariates. Statistical analyses were performed using R (v. 3.6.2; R Foundation, Vienna, Austria). Statistical significance was set at P < 0.05.
Results
Participants were 77% female and had a mean age of 72.1 ± 4.9 years. Higher IR scores were related to poorer performance on the Digit Symbol Substitution Test (β = −0.26, P = 0.04). IR scores were not related to other individual cognitive tests: Stroop Color (β = −0.17, P = 0.20), Stroop Word (β = −0.19, P = 0.11), Stroop Interference (β = −0.14, P = 0.28), Stroop Letter Number Sequencing (β = 0.03, P = 0.83), Crossing-Off (β = −0.18, P = 0.15), or Global SOP (β = −0.20, P = 0.11).
Conclusions
There was a relationship between higher IR scores and poorer performance on the Digit Symbol Substitution Test. Although other SOP tests were not significantly correlated with IR scores, directionality of the relationships indicated trend for higher IR being related to lower SOP. Consequently, maintaining insulin sensitivity with healthy lifestyle choices may be important for healthy aging. Future analyses with a larger sample size will be more informative for understanding the relationship between IR and SOP.
Funding Sources
National Institute on Aging.
Discriminant Validity of the WAIS-R Digit Symbol Substitution Test in Subjective Cognitive Decline, Mild Cognitive Impairment (Amnestic Subtype) and Alzheimer’s Disease Dementia (ADD) in Greece
