The study, published in the Annals of Epidemiology , followed almost 50,000 men and women and found that increasing consumption of the beverage among women decreased the risk of developing oral cancer, a disease with a higher proportion of deaths per number of cases than breast, skin, or cervical cancer, with a mortality rate of about 50 per cent due to late detection, according to British charity the Mouth Cancer Foundation.
The results, while not conclusive, add to an ever-growing body of science linking consumption to a wide range of health benefits, including lower risk of certain cancers, increased weight loss, improved heart health, and protection against Alzheimer's.
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.
The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.
The Japan Collaborative Cohort (JACC) Study Group, sponsored by the Ministry of Education, Science, Sports and Culture of Japan, analysed tea consumption using a comprehensive self-administered questionnaire amongst 20,550 men and 29,671 women (average age 57) in 24 areas of Japan.
During a mean follow-up period of 10.3 years, 37 oral cancer cases were documented by the researchers.
Of this total, 20 patients had died: 13 from oral cancer and seven from other causes.
After adjusting for potentially confounding factors, such as age, sex, smoking, and the consumption of alcohol, green and yellow vegetables, salty foods, fruit and coffee, lead author Reiko Ide and colleagues report that women who consumed five or more cups of green tea per day had an associated risk reduction of 70 per cent, compared to women who consumed between one and two cups per day.
However, due to the small number of oral cancer cases in the study group, this reduction was not classed as statistically significant.
For men, there was no tendency for protection against oral cancer observed, stated Ide.
The study had notable limitations, said the researchers.
Being epidemiological, no measures were made of the polyphenol content of the tea consumed, and no mechanistic study was performed to identify the active component or components of the beverages.
Also, questionnaires were only completed at baseline, raising questions about whether dietary habits changed over the course of the study.
"The Japanese population is unique in its long tradition of high consumption of green tea.
Additional epidemiologic studies are needed to evaluate the association between green tea consumption and oral cancer in Japan," concluded the researchers.
European demand for tea extracts is currently surging, and this has seen companies such as DSM, with its Teavigo boasting 95 per cent purity of EGCG, and Taiyo International, with its Sunphenon claiming more than 90 per cent purity, position themselves firmly in specific catechin markets.
Source: Annals of Epidemiology (Elsevier) Published on-line ahead of print, doi: 10.1016/j.annepidem.2007.04.003 "Prospective Study of Green Tea Consumption and Oral Cancer Incidence in Japan" Authors: R. Ide, Y. Fujino, Y. Hoshiyama, T. Mizoue, T. Kubo, T.-M. Pham, K. Shirane, N. Tokui, K. Sakata, A. Tamakoshi, T. Yoshimura, and for the JACC Study Group