Among participants with zero APOE-ε4 allele, 0.89% (95% CI 0.73–1.08%) current and 0.64% (95% CI 0.58–0.71%) former smokers developed dementia compared with 0.49% (95% CI 0.44–0.55%) of never smokers (adjusted HR 1.78; 95% CI 1.39–2.29; P = 0.01 and HR 1.23; 95% CI 1.05–1.46; P < 0.001, respectively) (Fig. 1a; Table 3). Here, APOE is linked to dementia.