Antiherpetic medication and incident dementia: observational cohort studies in four countries

Introduction Recent meta-analysis of the association between herpesvirus infection and dementia concluded that the evidence for an association to date is insufficient. Methods 2.5 million individuals aged ≥65 years were followed up using linked electronic health records in four national observational cohort studies. Exposure and outcome were classified using coded data from primary and secondary care. Data were analyzed using survival analysis with time-dependent covariates. Results Results: were heterogeneous, with a tendency towards decreased dementia risk in individuals exposed to antiherpetic medication. Associations were not affected by treatment number, herpes subtype, dementia subtype, or specific medication. In one cohort, individuals diagnosed with herpes but not exposed to antiherpetic medication were at higher dementia risk. Discussion Short-term antiherpetic medication is not markedly associated with incident dementia. Because neither dementia subtype nor herpes subtype modified the association, the small but significant decrease in dementia incidence with antiherpetic adminstration may reflect confounding and misclassification.