APOE and dementia: The results showed that the interaction between PPI use and APOE ε4 genotype was still present for all-cause dementia (P for interaction = 0.012; Additional file 1: Fig. S6), and the HR of PPI users among APOE ε4 heterozygote was 1.68 (95% CI, 1.36–2.07; P < 0.001).