Parkinson's disease and tea: a quantitative review

To evaluate the risk of PD associated with tea consumption.

We reviewed all observational studies that evaluated the association between PD risk and tea consumption. Only, 12 studies were identified: 11 case-control and 1 cohort. These studies were carried out between 1981 and 2003. The studies represented different populations from 3 continents; North America, Europe and Asia. The 3 studies from Asia were case-control studies of Chinese populations.

There was a clear protective effect of tea consumption in the pooled risk estimate [OR: 0.83 (95% confidence interval 0.74 to 0.92)] with 2215 cases and 145578 controls. However, the homogeneity test was significant (p value of 0.008), denoting heterogeneity across the pooled studies. Pooled analysis applying the random effect model was OR: 0.81 with 95% confidence interval nearly overlapping unity (95% confidence interval 0.67 to 0.98). Tea consumers versus non-consumers in Chinese populations had pooled OR of 0.73 with 95% confidence interval 0.60 to 0.90 (470 cases and 623 controls). The p value of homogeneity test was 0.96, denoting homogeneity across the pooled 3 studies.

Tea consumption can protect against PD and this protective effect is clearer in Chinese populations. The low rate of tea consumption among persons with PD should provide us many valuable insights into the nature of the illness.