Drinking tea may protect against Parkinson's Disease
A review of the current literature has concluded that tea consumption may provide protection from Parkinson's Disease (PD), the results being most striking in Chinese populations.
The lower rates of cardiovascular disease and cancer in Asian populations have been attributed, by some, to tea consumption. The prevalence of PD in Chinese populations is much lower than in Caucasian populations and some have also linked this to a high tea consumption.
The present study involved a comprehensive review of published data investigating the association between PD and tea consumption.
Published observational studies on PD and tea consumption were identified through a comprehensive search including MEDLINE and PsycLIT. Twelve studies were identified based on the inclusion criteria: 11 case-control and 1 cohort study published between 1981 and 2003. The studies represented different populations from 3 continents; North America, Europe and Asia.
Data were extracted from each study in the form of a risk estimate (odds ratio, OR) and its 95% confidence interval. Pooled risk estimates were calculated and the validity of this pooling was then tested (the test of homogeneity). If this test was significant, denoting heterogeneity across the studies (i.e. studies being grouped together differed from one another), a random effects analysis was performed instead. The random effects analysis accounts for the heterogeneity between different studies. The pooled OR for all 12 studies investigating the risk of PD in tea consumers versus non-consumers suggested a protective effect of tea (pooled OR, 0.83; 95% CI, 0.74-0.92) and included 2,215 cases and 145,578 controls. However the test for homogeneity was significant and therefore the random effects analysis was applied (OR, 0.81; 95% CI, 0.67-0.98). As these results were close to no effect, in reality there may be little effect of tea drinking on PD. However, pooling the results of the 7 case-control studies using only population based controls showed a clear, protective effect (OR, 0.76; 95% CI, 0.66-0.88) with homogeneity between the populations. Therefore it could be that the reason for heterogeneity when all the studies were analysed is due to the study design, i.e. population based versus hospital based. The risk of PD according to numbers of cups of tea consumed was also assessed. Three case-control studies had sufficient data to calculate the risk for consumers of ≤1 cup of tea per day compared to non-consumers. The pooled OR indicated a probable protective effect of drinking up to one cup per day (pooled OR, 0.75; 95% CI, 0.60-0.93). Four case-control studies had sufficient data to calculate the risk for consumers of >1 cup of tea per day compared to non-consumers. However the 95% confidence interval crosses the line of no effect (pooled OR, 0.81; 95% CI, 0.64-1.03) and thus is not significant.
Pooled data for the 3 studies carried out in Chinese populations was homogeneous with a suggestion that tea drinking is protective against PD in this population (pooled OR, 0.73; 95% CI, 0.60-0.90).
The limited number of identified studies on tea consumption and PD reveal it is an under researched area. Nevertheless the findings of a protective effect of tea consumption are encouraging and warrant further research to confirm the association and to quantify the level of consumption needed in order to confer protection.
Quintana, J.L.B., Allam, M. F., Del Castillo, A. S. and Navajas, R. F. (2009). Parkinson's Disease and Tea: A Quantitative review. J. Am. Coll. Nutr. 28:1, 1-6.
