Associations of Chinese Herbal Medicine Usage with Risk of Dementia in Patients with Parkinson's Disease: A Population-Based, Nested Case–Control Study

Background: Patients who have Parkinson's disease (PD) comorbid with dementia is common. With the prolonged life expectancy, dementia is gradually becoming prevalent and affects most patients' life qualities. However, the efficacy of current treatments in dementia of PD is limited. Previous studies indicated the potential roles of Chinese herbal medicine (CHM) in treating dementia, yet the correlation between CHM usage and risk of dementia in PD patients is unclear. Methods: This case-control study was nested within a National Health Insurance database of patients over 50 years with newly diagnosed PD from year 2000 to 2010. Among these PD patients, dementia and nondementia groups were discussed, respectively, in terms of the duration of taking CHM (≥90 vs. <90 days), age (50-64 vs. ≥65 years) and gender. Results: The risk of dementia in patients with PD is lower in CHM users compared with non-CHM users, especially in those taking CHM for more than 90 days (adjusted odds ratio [aOR] 0.58; 95% confidence interval [95% CI] 0.39-0.87). The use of CHM was significantly related to the lower risk of dementia in the subgroups of patients with age ≥65 years for CHM usage <90 days (aOR 0.68; 95% CI 0.53-0.88), patients with age ≥65 years for CHM usage ≥90 days (aOR 0.63; 95% CI 0.42-0.94), female patients using CHM for ≥90 days (aOR 0.43; 95% CI 0.22-0.84), and male patients using CHM for <90 days (aOR 0.62; 95% CI 0.43-0.88). Conclusions: The authors demonstrated the association of CHM usage with lower risk of dementia in patients with PD, especially in women with the usage of CHM for more than 90 days. Since no arbitrary causal conclusions could be drawn from retrospective cohort studies, the finding in this study could be used to generate a hypothesis for a subsequent design of prospective longitudinal study.