Results have been inconsistent because of restricted statistical power, as some studies indicated no interaction between genetic risk and cardiovascular risk factors16, 33 whereas others suggest factors such as midlife smoking increase dementia risk in APOE ε4 carriers but not non-carriers,34 and a favourable risk profile corresponded to a reduced dementia risk in APOE ε4 non-carriers only.17 Here, APOE is linked to dementia.