There was a significant negative interaction between APOE ε4 status and type 2 diabetes on the risk of dementia for all-cause dementia (HR for interaction term 0.62, P = 0.011), as well as Alzheimer’s disease (HR 0.46, P = 0.047), but not for mixed dementia or vascular dementia. The gene discussed is APOE; the disease is Alzheimer disease.