This retrospective cohort study is to investigate the association between herpes simplex virus (HSV) infections and dementia, and the effects of anti-herpetic medications on the risk involved, using Taiwan's National Health Insurance Research Database (NHIRD). We enrolled a total of 33,448 subjects, and identified 8362 with newly diagnosed HSV infections and 25,086 randomly selected sex- and age-matched controls without HSV infections in a ratio of 1:3, selected from January 1, to December 31, 2000. A multivariable Cox proportional hazards regression model was used to evaluate the risk of developing dementia in the HSV cohort. This analysis revealed an adjusted hazard ratio of 2.564 (95% CI: 2.351-2.795, P < 0.001) for the development of dementia in the HSV-infected cohort relative to the non-HSV cohort. Thus, patients with HSV infections may have a 2.56-fold increased risk of developing dementia. A risk reduction of dementia development in patients affected by HSV infections was found upon treatment with anti-herpetic medications (adjusted HR = 0.092 [95% CI 0.079-0.108], P < 0.001). The usage of anti-herpetic medications in the treatment of HSV infections was associated with a decreased risk of dementia. These findings could be a signal to clinicians caring for patients with HSV infections. Further research is, therefore, necessary to explore the underlying mechanism(s) of these associations.

Background: Chronic periodontitis and gingivitis are associated with various diseases; however, their impact on dementia is yet to be elucidated. This study is aimed at investigating the association between chronic periodontitis and gingivitis, and the risk of developing dementia. Methods: A total of 2,207 patients, with newly diagnosed chronic periodontitis and gingivitis between January 1, 2000 and December 31, 2000, were selected from the National Health Insurance Research Database of Taiwan, along with 6,621 controls matched for sex and age. After adjusting for confounding factors, Cox proportional hazards analysis was used to compare the risk of developing dementia during the 10-year follow-up period. Results: Of the study subjects, 25 (1.13%) developed dementia compared to 61 (0.92%) in the control group. Cox proportional hazards regression analysis revealed that the study subjects were more likely to develop dementia (hazard ratio (HR) 2.085, 95% CI 1.552-4.156, p < 0.001). After adjusting for sex, age, monthly income, urbanization level, geographic region, and comorbidities, the HR for dementia was 2.54 (95% CI 1.297-3.352, p = 0.002). Conclusions: Patients with chronic periodontitis and gingivitis have a higher risk of developing dementia. However, further studies on other large or national data sets are required to support the current findings.

Adults with ADHD have a 3.4-fold risk of developing dementia, and other large or national data sets should be explored to support the current findings.