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New Health Study on Benefits of Green Tea
Results Vary for Men and Women - Over 50,000 People Included in Study
By Stephen Daniells
8/22/2007- Drinking five or more cups of green tea a day may reduce a
woman's risk of mouth cancer, but men may not experience similar
benefits, suggests a new study from Japan.
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. |
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Green Tea Contains More Polyphenols Than Black Tea
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. |
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Some Notable Limitations of the Study
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.
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More Research Needed - Rise of Catechin Markets
"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 |
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