Lower levels of Aβ1–38 and Aβ1–42 were associated with increased risk of dementia, specifically AD (HR for AD per SD decrease in Aβ1–38 levels, 1.39; 95% CI, 1.00–2.16; HR for AD per SD decrease in Aβ1–42 levels, 1.35; 95% CI, 1.05–1.75) after adjustment for age, sex, education, cardiovascular risk factors, apolipoprotein E ε4 allele carrier status, and other Aβ isoforms. This evidence concerns the gene APOE and Alzheimer disease.