Science

Laura L. Ekblad, MD, Jarkko Johansson, PhD, Semi Helin, MSc, Matti Viitanen, PhD, Hanna Laine, PhD, Pauli Puukka, MSocSc, Antti Jula, PhD, and Juha O. Rinne, PhD

Objective
To examine whether midlife insulin resistance is an independent risk factor for brain amyloid accumulation in vivo after 15 years, and whether this risk is modulated by APOE4 genotype.
Methods
This observational study examined 60 elderly volunteers without dementia (mean age at
baseline 55.4 and at follow-up 70.9 years, 55.5% women) from the Finnish population-based, nationwide Health2000 study with [11C]Pittsburgh compound B–PET imaging in 2014–2016. The participants were recruited according to their homeostatic model assessment of insulin resistance (HOMA-IR) values in the year 2000, and their APOE e4 genotype. The exposure group (IR+, n = 30) consisted of individuals with HOMA-IR >2.17 at baseline (highest tertile of the Health2000 study population), and the control group (IR−, n = 30) consisted of individuals with HOMA-IR < 1.25 at baseline (lowest tertile). The groups were enriched for APOE4 carriers, resulting in 50% (n = 15) APOE e4 carriers in both groups. Analyses were performed with multivariate logistic and linear regression. Results An amyloid-positive PET scan was found in 33.3% of the IR− group and 60.0% of the IR+ group (odds ratio 3.0, 95% confidence interval 1.1–8.9, p = 0.04). The increased risk was seen in carriers and noncarriers of APOE e4 genotype. Higher midlife, but not late-life continuous HOMA-IR was associated with a greater brain amyloid burden at follow-up after multivariate adjustments for other cognitive and metabolic risk factors (β = 0.11, 95% confidence interval 0.002–0.22, p = 0.04). Conclusions These results indicate that midlife insulin resistance is an independent risk factor for brain amyloid accumulation in elderly individuals without dementia.