Association of Midlife Plasma Amyloid-β Levels With Cognitive Impairment in Late Life: The ARIC Neurocognitive Study

BACKGROUND AND OBJECTIVES: To evaluate the association between midlife plasma amyloid-β (Aβ1-42, Aβ1-40, Aβ42:Aβ40) and risk of mild cognitive impairment (MCI) and dementia. METHODS: Plasma Aβ42 and Aβ40 were retrospectively measured with a fluorometric bead-based immunoassay in a subsample of the Atherosclerosis Risk in Communities cohort study. We investigated the relationship of plasma Aβ42, Aβ40, and Aβ42:Aβ40 ratio measured in midlife and late life and the change from midlife to late life to risk of MCI, dementia, and combined MCI/dementia outcomes in late life (from 2011-2019). We used multinomial logistic regressions estimating relative risk ratios (RRRs) of these cognitive outcomes vs cognitively normal adjusted for age, sex, education, site-race, APOE, hypertension, diabetes, and body mass index. RESULTS: A total of 2,284 participants were included (midlife mean age 59.2 ± 5.2, 57% female, 22% Black). Each doubling of midlife Aβ42:Aβ40 was associated with 37% lower risk of MCI/dementia (RRR 0.63, 95% confidence interval [CI] 0.46-0.87), but only up to approximately the median (spline model threshold 0.20). Every 1-SD increase in plasma Aβ42 (10 pg/mL) was associated with 13% lower risk of MCI/dementia (RRR 0.87, 95% CI 0.77-0.98), whereas every 1-SD increase in plasma Aβ40 (67 pg/mL) was associated with 15% higher risk of MCI/dementia (RRR 1.15, 95% CI 1.01-1.29). Associations were comparable but slightly weaker statistically when models were repeated using late-life plasma Aβ predictors. Aβ42 and Aβ40 increased from midlife to late life, but changes were not associated with cognitive outcomes. DISCUSSION: Midlife measurement of plasma Aβ may have utility as a blood-based biomarker indicative of risk for future cognitive impairment.