Researchers at Taiwan's National Defense Medical Center followed 33,448 people in the national health insurance database, comparing dementia rates between those newly diagnosed with herpes simplex infections and age- and sex-matched people without the diagnosis.
People with a herpes simplex diagnosis had about 2.6 times the risk of later developing dementia compared with matched controls. Among those with herpes infections, the subgroup treated with antiviral medication had a far lower dementia risk than the untreated subgroup, a difference large enough that the authors flagged it as a signal worth testing directly.
This was a single-country, insurance-database study, not a randomized trial, and reliant on diagnostic codes rather than direct brain measurement, so it cannot prove the virus or the antivirals caused the dementia difference. A 2025 randomized trial of valacyclovir in people with early Alzheimer's and herpes antibodies found no benefit, with slightly faster cognitive decline on the drug.
Read the original study
Tzeng et al., Neurotherapeutics, 2018 · doi.org/10.1007/s13311-018-0611-x
A virus hiding in the brain tied to dementia.
Source
- Tzeng, N.-S., Chung, C.-H., Lin, F.-H., Chiang, C.-P., Yeh, C.-B., Huang, S.-Y., Lu, R.-B., Chang, H.-A., Kao, Y.-C., Yeh, H.-W., Chiang, W.-S., Chou, Y.-C., Tsao, C.-H., Wu, Y.-F., & Chien, W.-C. (2018). Anti-herpetic Medications and Reduced Risk of Dementia in Patients with Herpes Simplex Virus Infections-a Nationwide, Population-Based Cohort Study in Taiwan. Neurotherapeutics, 15(2), 417–429. https://doi.org/10.1007/s13311-018-0611-x