Prior research on dementia risk reported interactions between APOE4 and smoking in the UK Biobank [8] and between APOE4 and depression in Canadian Study of Health and Aging, [9] while other studies have reported no interaction between smoking, [8] healthy lifestyle, [10, 11] or self-reported hearing loss [12] and polygenic risk for dementia [8, 10, 12, 13] or cognitive decline [11, 12]. This evidence concerns the gene APOE and major depressive disorder.