Why Green Tea Does Not Reduce Cancer Risk in Northeast Japan?

- A Japanese Study Reported in JAMA (page 360) January 24 issue, 2007

- The U.S. FDA (link to Landa’s June 30, 2005 letter) also found that it is highly unlikely that the green tea consumed in northeast Japan reduces the risk of breast cancer or prostate cancer whereas the green tea consumed by the Asian Americans living in Los Angeles or by the residents of Hangzhou City may reduce the risk of breast cancer and prostate cancer, respectively.

In a reply to Dr. Sin Hang Lee’s Letter to the Editor of the Journal of American Medical Association, Dr. Kuriyama and Colleagues stated that “Our study found a statistically nonsignificant increase in the risk of cancer death among participants who consumed 5 or more cups of green tea per day…” in 14 municipalities of Miyagi in the Tohoku (Northeast) region of Japan. This finding is contrary to those of 15 other Japanese studies referenced below [1-15], which all show a reduced cancer risk associated with green tea consumption. It all depends on what green tea is used and how the tea is prepared, explains Dr. Lee as follows:

There are other studies in Japan that failed to find a connection between green tea consumption and a reduced stomach cancer rate. One group of authors concluded: “This failure may be due to some crudeness in the assessment of green tea intake; green tea consumption was determined only in terms of self-reported daily frequency of drinking, and the highest category was five or more cups per day. Bioactivity of a cup of green tea obviously differs by the amount of green tea leaves used to brew it and the frequency of renewing a tea batch in the pot. In Shizuoka prefecture, which has the highest production of green tea leaves in Japan, residents of towns with low mortality from stomach cancer were found not only to drink green tea more frequently, but also to renew tea leaves more frequently than those of a town with high mortality from stomach cancer [16] .”

Numerous grades of green tea leaves are sold on the Japanese market, all under the generic name Sencha. A high-grade Sencha may contain 7.51% EGCG in dry weight; and Hojicha is the lowest grade of Sencha with only 1.68% EGCG [17]. High-grade green teas are expensive. They are the beverage of the aristocrats in Japan and are also consumed by the residents living in the tea plantation regions. According to a Japanese Cabinet Office report on “Regional Income Gap and Dependency on Public Investment” [18], Miyagi, a non-tea producing prefecture, is one of 22 prefectures with lower income levels that have high dependence on public investment to maintain their local economy. During the cold winters, many of Tohoku’s farmers move to Tokyo and other cities for seasonal work in construction and factories. Many young people move away too, often permanently, to enter the labor market and build careers in other regions [19]. Since the participants in answering Dr. Kuriyama’s self-reported questionnaires were the less mobile “residents of 14 municipalities in Miyagi Prefecture” [20], it is conceivable that some subjects recruited in the study were Hojicha drinkers living in the rural municipalities in which the bioactivity of the green tea consumed may be below the lowest effective anticancer dose in humans based on the pharmacodynamic data calculated from animal studies [21].

Another confounding factor in studying green tea health effects in the “Northeast” of Japan is the local custom of the residents of Tohoku to put their traditional cast-iron teapots atop the stoves during the long winters [22]. The ferrous/ferric ions extracted by the hot tea will form metal complexes with the tea catechins and invariably act as an electron shuttle between catechin molecules and the atmospheric oxygen, like the iron in the human red blood cells, turning the tea catechins into less bioactive polymerized polyphenols [23]. In addition, cast iron contains polycyclic aromatic hydrocarbons (PAHs), a well-known carcinogen [24]. The high cancer mortality associated with green tea consumption in Miyagi may be caused by the carcinogens extracted from the cast-iron teapots by the hot water during prolonged heating. It is important for the readers to be aware of the limitation of the Miyagi study.

References

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[2] Fujiki H, Suganuma M, Okabe S, et al. Cancer prevention with green tea and monitoring by a new biomarker, hnRNP B1. Mutat Res 2001;480-481:299-304.

[3] Goto R, Masuoka H, Yoshida K, et al. A case control study of cancer of the pancreas. Gan No Rinsho 1990 Feb;Spec No:344-50 [Article in Japanese]

[4] Imai K, Suga K, Nakachi K. Cancer-preventive effects of drinking green tea among a Japanese population. Prev Med 1997;26:769-775.

[5] Inoue M, Tajima K, Hirose K, et al. Tea and coffee consumption and the risk of digestive tract cancers: data from a comparative case-referent study in Japan. Cancer Causes Control. 1998;9:209-16.

[6] Ioue M, Tajima K, Mizutani M, et al. Regular consumption of green tea and the risk of breast cancer recurrence: follow-up study from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), Japan. Cancer Lett 2001;167:175-82.

[7] Kato I, Tominaga S, Matsuura A, et al. A comparative case-control study of colorectal cancer and adenoma. Jpn J Cancer Res. 1990;81:1101-8.

[8] Kono S, Ikeda M, Tokudome S, et al. A case-control study of gastric cancer and diet in northern Kyushu, Japan. Jpn J Cancer Res. 1988 ;79:1067-74.

[9] Kono S, Shinchi K, Ikeda N, et al. Physical activity, dietary habits and adenomatous polyps of the sigmoid colon: a study of self-defense officials in Japan. J Clin Epidemiol 1991;44:1255-61.

[10] Nakachi K, Eguchi H, Imai K. Can teatime increase one's lifetime? Ageing Res Rev 2003;2:1-10.

[11] Nakachi K, Matsuyama S, Miyake S, et al. Preventive effects of drinking green tea on cancer and cardiovascular disease: epidemiological evidence for multiple targeting prevention. BioFactors 2000;13:49-54.

[12] Nakachi K, Suemasu K, Suga K, et al. Influence of drinking green tea on breast cancer malignancy among Japanese patients. Jpn J Cancer Res. 1998;89:254-61.

[13] Ohno Y, Aoki K, Obata K, et al. Case-control study of urinary bladder cancer in metropolitan Nagoya. Natl Cancer Inst Monogr. 1985;69:229-34.

[14] Ohno Y, Wakai K, Genka K, et al. Tea consumption and lung cancer risk: a case-control study in Okinawa, Japan. Jpn J Cancer Res. 1995;86:1027-34.

[15] Wakai K, Ohno Y, Obata K, et al. Prognostic significance of selected lifestyle factors in urinary bladder cancer. Jpn J Cancer Res 1993 ;84:1223-9.

[16] Nagano J, Kono S, Preston DL, et al. A prospective study of green tea consumption and cancer incidence, Hiroshima and Nagasaki (Japan). Cancer Causes Control 2001;12:501-8.

[17] Fujiki H. Green tea: Health benefits as cancer preventive for humans. Chem Rec 2005;5:119-132.

[18] http://www.mhlw.go.jp/english/wp/l-economy/2005/dl/02-01-03.pdf

[19] East Asian Region -Japan - http://www.ibiblio.org/chinesehistory/contents/04ear/c02.html

[20] Kuriyama S, Shimazu T, Ohmori K, et al. Green tea consumption and mortality due to cardiovascular disease, cancer and all causes in Japan. JAMA 2006; 296:1255-1265.

[21] NCI, DCPC Chemoprevention Branch and Agent Development Committee. Clinical development plan: tea extracts. Green tea polyphenols. Epigallocatechin gallate. J. Cell Biochem Suppl. 1996;26:236-257.

[22] http://www.answers.com/topic/t-hoku-region

[23] Kumamoto M, Sonda T, Nagayama K, et al. Effects of pH and metal ions on antioxidative activities of catechins. Biosci Biotechnol Biochem. 2001;65:126-32.

[24] Moulin JJ, Portefaix P, Wild P, Mur JM, Smagghe G, Mantout B. Mortality study among workers producing ferroalloys and stainless steel in France. Br J Ind Med. 1990;47:537-43.

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