Drinking five or more cups of green tea per day may reduce the risk of blood- and lymph-based cancers by about 50 per cent, says a new study from Japan.
Compared to people who drank only one cup per day, five cups of green tea a day were associated with a 42 per cent reduction in hematologic malignancies, and a 48 per cent risk reduction in lymphoid neoplasms, according to findings published in the American Journal of Epidemiology.
The study, led by Toru Naganuma from Tohoku University School of Medicine in Japan, adds to the ever-growing body of science supporting the anti-cancer benefits of green tea and its polyphenols.
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).
Naganuma and his co-workers followed 41,761 adults participating in the Ohsaki National Health Insurance Cohort Study. A questionnaire completed at the start of the study allowed the researchers to quantify green tea consumption.
During nine years of follow-up, the researchers documented 157 hematologic malignancies, including 119 cases of lymphoid neoplasms and 36 cases of myeloid neoplasms.
The risk reductions observed for people who drank five or more cups a day, compared to those who drank only cup, was not affected by the gender of the participants, or their body mass index.
While the result does not prove causality, it does support other studies which reported a protective effect of green tea and its constituents.
Being an epidemiological study, 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.
Global tea market
The global tea market is worth about €790 (£540, $941) million, with green tea accounting for about 20 per cent of total global production, while black tea accounts for about 78 per cent.
Consumer awareness of the benefits of green tea and green tea extracts continues to rise with growing numbers of studies, from 430 papers in 2000 to almost 1500 in 2003, reporting benefits of the main compounds, catechins.
This has seen European demand surge, having reached 500 metric tonnes in 2003. Companies such as DSM, with its Teavigo boasting 95 per cent purity of epigallocatechin gallate (EGCG), and Taiyo International, with its Sunphenon claiming more than 90 per cent purity, position themselves firmly in specific catechin markets.
Source: American Journal of Epidemiology
Published online ahead of print, doi:10.1093/aje/kwp187
“Green Tea Consumption and Hematologic Malignancies in Japan - The Ohsaki Study”
Authors: T. Naganuma, S. Kuriyama, M. Kakizaki, T. Sone, N. Nakaya, K. Ohmori-Matsuda, A. Hozawa, Y. Nishino, I. Tsuji