Tea and Cancer Prevention: An Evaluation of the Epidemiological Literature
Lenore Kohlmeier, Karen G C Weterings, Susan Steck, and Frans J Kok

Animal and in vitro studies provide evidence of an anticarcinogenic potential of active ingredients in teas. This review encompasses epidemologic studies of stomach, colon and lung cancer as well as the evidence of a relationship between tea drinking and cancer at large in humans. Cohort studies do not suggest a protective role for tea drinking in the total risk of cancer. Site-specific studies reveal a more complex picture. The epidemiological studies on tea drinking and stomach cancer do not justify claims of a cancer-protective effect. A protective effect of green tea on the development of colon cancer is suggested. The evidence regarding black tea is less clear, with some indication of a risk of colon or rectal cancer associated with regular use of black tea. The studies on tea and lung cancer also suggest an increased risk with increased tea consumption. The range and crude categorisation of tea consumption, choice of control groups and inadequate control for confounding might have obscured possible relationships. From the limited studies that suggest a favourable effect from tea, it is likely that benefits are restricted to high intakes in high-risk populations.

Flavonoid Constituents of Chorizanthe diffuse with Potential Cancer Chemopreventive Activity
Ha Sook Chung, Leng Chee Chang, Sang Kook Lee, Lisa A. Shamon, Richard B. van Breemen, Rajendra G.Mehta, Norman R. Farnsworth, John M. Pezzuto, and A. Douglas Kinghorn. -- Program for Collaborative Research in the Pharmaceutical Sciences and Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, and Department Surgical Oncology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612.

An ethyl acetate-soluble extract of Chorizanthe diffusa was found to exhibit significant antioxidant activity, as judged by scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals and inhibition of 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced free radical formation with cultured HL-60 cells. Bioassay-directed fractionation of this extract using ghe DPPH antioxidant assay as a monitor led to the isolation of five structurally related flavonoids (1-5), including the novel compound 5,8,3’,4’,5’-pentahydroxy-3,7-dimethoxyflavone (1). Isolates 1-5 demonstrated varying degrees of antioxidant or antimutagenic activity. Two of the compounds, 5,7,3’,4’-tetrahydroxy-3-methoxyflavone (2) and quercetin (4), were subsequently found to inhibit carcinogen-induced preneoplastic lesions in a mouse mammary organ culture model. Inhibitory activity of this type is known to correlate with cancer chemopreventive effects in full-term models of tumorigenesis.

Tea Consumption and Cancer Incidence in a Prospective Cohort Study of Postmenopausal Women
Wel Zheng.1 Timothy J Doyle.2 Lawrence H.Kushi.1Thomas A Sellers, 1 Ching-Ping Hong1 and Aaron B Felsom’ Am J Epidemiol 1996; 144; 175-82.

Tea has consistently been shown to inhibit the occurrence of tumors in experimental animals. The evidence for such a beneficial effect in humans, however, it limited. The authors examined the association between non-herbal tea consumption and cancer incidence in a prospective cohort study of 35,369 postmenopausal Iowa women. In this cohort, information on the frequency of tea drinking and other dietary and lifestyle factors was collected by mailed survey in 1986. After 8 years of follow-up, 2,936 incident non-skin cancer cases were ascertained in this cohort through the State Health Registry of Iowa. Proportional hazards regressions were used to derive adjusted relative risks and 95% confidence intervals for the association between tea consumption and cancer incidence. After controlling for confounding factors, the authors found that regular tea consumption was related to a slight, but not statistically significant, reduced incidence of all cancers combined. Inverse associations with increasing frequency of tea drinking were seen for cancers of the digestive tract (p for trend, 0.04) and the urinary tract (p for trend, 0.02). For women who reported drinking > 2 cups (474 ml) of tea per day, compared with those who never or occasionally drank tea, the relative risk for digestive tract cancers was 0.68 (95% confidence interval (CI) 0.47-0.98) and for urinary tract cancers, 0.40 (95% CI 0.16-0.98). Similar inverse associations were seen for specific digestive and urinary tract cancers, although site-specific analyses were not statistically significant. No appreciable association of tea drinking was fond with melanoma, non-Hodgkin’s lymphoma, or cancers of the pancreas, lung, breast, uterine corpus, or ovary. This study suggests that tea, one of the most popular beverages consumed worldwide, may protect against some cancers in postmenopausal women.

Compounds in tea inhibit the progression of major cancers
Weisburger-J-H, Hara-Y, Dolan-L, Luo-F-Q, Pittman-B, Zang-E, Mutat-Res 1996 Nov 4, VOL: 371(1-2), P: 57-63, ISSN: 0027-5107.

Previous research suggested that the mutagenicity of some genotoxic carcinogens, mainly heterocyclic amines, was decreased by green or black tea extracts, or tea polyphenol fractions. Thus, it seemed important to test a variety of genotoxic carcinogens with distinct chemical structures and means of biochemical activations as regards modification of mutagenicity in appropriate strains of Salmonella typhumurium by 3 concentrations of polyphenols 60, 100 or B, standard commercial polyphenol preparations from green or black tea.

Polyphenols sharply decreased the mutagenicity of a number of aryl-and heterocyclic amines, of aflatoxin B1, bonzo (a) pyrene, 1,2-dibromoethane, and more selectively, of 2-nitorpropane, all involving an induced rat liver S9 fraction. Good inhibition was found with 2 nitrosamines that required a hamster S9 fraction for biochemical activation. No effect was found with 1-nitropyrene, and with the direct acting (noS9) 2-chloro-4-methyl-thiobutanoic acid. Thus, with some exceptions, polyphenols considerably decreased the mutagenicity of diverse types of carcinogens.