Higher fasting insulin levels and increased insulin resistance predict future memory decline as measured by verbal fluency. About 4,000 individuals, average age 50, were followed for 11 years. These findings imply the need of addressing insulin resistance early rather then later, when prediabetes or diabetes emerge.
Objective: The aim of this study was to examine whether insulin resistance, assessed by HOMA of insulin resistance (HOMA-IR), is an independent predictor of cognitive decline.
Research Design and Methods: The roles of HOMA-IR, fasting insulin and glucose, HbA1c, and hs-CRP as predictors of cognitive performance and its change were evaluated in the Finnish nationwide, population-based Health 2000 Health Examination Survey and its 11-year follow-up, the Health 2011 study (n = 3,695, mean age at baseline 49.3 years, 55.5% women). Categorical verbal fluency, word-list learning, and word-list delayed recall were used as measures of cognitive function. Multivariate linear regression analysis was performed and adjusted for previously reported risk factors for cognitive decline.
Higher baseline HOMA-IR and fasting insulin levels were independent predictors of poorer verbal fluency performance (P = 0.0002 for both) and of a greater decline in verbal fluency during the follow-up time (P = 0.004 for both).
Baseline HOMA-IR and insulin did not predict word-list learning or delayed recall scores.
There were no interactions between HOMA-IR and apolipoprotein E ε4 (APOEε4) genotype, hs-CRP, or type 2 diabetes on the cognitive tests.
Fasting glucose and hs-CRP levels at baseline were not associated with cognitive functioning.
Our results show that higher serum fasting insulin and insulin resistance predict poorer verbal fluency and a steeper decline in verbal fluency during 11 years in a representative sample of an adult population.
Prevention and treatment of insulin resistance might help reduce cognitive decline later in life.