The benefits of the beverage were not linked to the caffeine content, suggest the results of the study of 63,257 Chinese men and women published in the American Journal of Epidemiology. Parkinson's disease is a degenerative condition affecting movement and balance in more than one million Americans each year, a figure expected to rise due to ageing populations. Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent. Oolong tea is semi-fermented tea and is somewhere between green and black tea. The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).
Despite results from previous studies reporting that green tea may reduce the risk of Parkinson's, the new study, reported no benefits among participants of the Singapore Chinese Health Study. Lead author Louis Tan from Singapore's National Neuroscience Institute states that data was collected through in-person interviews using structured questionnaires. Over the course of the study, 57 incident cases of Parkinson's disease were documented, and while caffeine was associated with a protective effect, reducing disease risk by 45 per cent, the benefits of black tea were not affected by caffeine content, wrote Tan and co-authors. "Black tea, a caffeine-containing beverage, showed an inverse association with Parkinson's disease risk that was not confounded by total caffeine intake or tobacco smoking," wrote the authors.
"Ingredients of black tea other than caffeine appear to be responsible for the beverage's inverse association with Parkinson's disease," they concluded. Tea Advisory Panel welcomes the results Commenting on the study, Dr Ann Walker, a member of The Tea Advisory Panel (TAP) said that the latest research study was great news for all UK 'black tea' drinkers. "In the past there seems to have been more of a focus by scientists reviewing the health benefits of green tea," she said.
She added that previous studies looking at tea drinking and Parkinson's disease risk did not differentiate between black tea and green tea, while the protective effect of tea were attributed to the caffeine content. "In the current study, however, the beneficial effect of black tea did not appear to be influenced by caffeine intake, indicating that ingredients other than caffeine are responsible for black tea's protective effects," said Dr. Walker. "A key difference between black tea and green tea lies in the types and amounts of flavonoids. Green teas contain more of the simple flavonoids called catechins. But when black tea is made, the catechins undergo oxidation resulting in the generation of more complex varieties, called thearubigins and theaflavins." "The underlying mechanisms for this protective effect of black tea on Parkinson's disease remains unclear until further research is done. But drinking even one cup of black tea per day could help to reduce the risk of Parkinson's disease," she concluded.
Source: American Journal of Epidemiology Published online ahead of print 20 December 2007, doi: doi:10.1093/aje/kwm338 "Differential Effects of Black versus Green Tea on Risk of Parkinson's Disease in the Singapore Chinese Health Study"
Authors: Louis C. Tan, W.-P. Koh, J.-M. Yuan, R. Wang, W.-L. Au, J.H. Tan, E.-K. Tan, M.C. Yu