1: Altern Ther Health Med 2000 May;6(3):61-8, 70-2, 74 Green tea monograph. McKenna DJ, Hughes K, Jones K. Institute for Natural Products Research, St. Croix, MN 55047, USA.Green Tea Description and Constituents
"Tea is one of the most widely consumed beverages in the world today, second only to water, and its medicinal properties have been widely explored. The tea plant, Camellia sinensis, is a member of the Theaceae family, and black, oolong, and green tea are produced from its leaves. It is an evergreen shrub or tree and can grow to heights of 30 feet, but is usually pruned to 2-5 feet for cultivation. The leaves are dark green, alternate and oval, with serrated edges, and the blossoms are white, fragrant, and appear in clusters or singly. Unlike black and oolong tea, green tea production does not involve oxidation of young tea leaves.
Green tea is produced from steaming fresh leaves at high temperatures, thereby inactivating the oxidizing enzymes and leaving the polyphenol content intact. The polyphenols found in tea are more commonly known as flavanols or catechins and comprise 30-40 percent of the extractable solids of dried green tea leaves. The main catechins in green tea are epicatechin, epicatechin-3-gallate, epigallocatechin, and epigallocatechin-3-gallate (EGCG), with the latter being the highest in concentration. Green tea polyphenols have demonstrated significant antioxidant, anticarcinogenic, anti-inflammatory, thermogenic, probiotic, and antimicrobial properties in numerous human, animal, and in vitro studies.1,2
Mechanisms of Action The anticarcinogenic properties of green tea polyphenols, mainly EGCG, are likely a result of inhibition of biochemical markers of tumor initiation and promotion, induction of apoptosis, and inhibition of cell replication rates, thus retarding the growth and development of neoplasms.3,4 Their antioxidant potential is directly related to the combination of aromatic rings and hydroxyl groups that make up their structure, and is a result of binding and neutralization of free radicals by the hydroxyl groups. In addition, green tea polyphenols stimulate the activity of hepatic detoxification enzymes, thereby promoting detoxification of xenobiotic compounds, and are also capable of chelating metal ions, such as iron, that can generate radical oxygen species.5,6
Green tea polyphenols inhibit the production of arachidonic acid metabolites such as pro-inflammatory prostaglandins and leukotrienes, resulting in a decreased inflammatory response.
Human and animal studies have demonstrated EGCG's ability to block inflammatory responses to ultraviolet A and B radiation as well as significantly inhibiting the neutrophil migration that occurs during the inflammatory process.7-9 Research on green tea's thermogenic properties indicates a synergistic interaction between its caffeine content and catechin polyphenols may result in prolonged stimulation of thermogenesis. Studies have also shown green tea extracts are capable of reducing fat digestion by inhibiting digestive enzymes.10,11
Although the exact mechanism is unknown, green tea catechins have been shown to significantly raise levels of Lactobacilli and Bifidobacteria while decreasing levels of numerous potential pathogens.12 Studies have also demonstrated green tea's antibacterial properties against a variety of gram-positive and gram-negative species.
Clinical Indications Cancer Prevention/Inhibition: Several studies have demonstrated green tea polyphenols' preventative and inhibitory effects against tumor formation and growth. While the studies are not conclusive, green tea polyphenols, particularly EGCG, may be effective in preventing cancer of the prostate, breast, esophagus, stomach, pancreas, and colon.14 There is also some evidence that green tea polyphenols may be chemopreventative or inhibitory toward lung, skin, and liver cancer,15-17 bladder and ovarian tumors,18,19 leukemia,20 and oral leukoplakia.21
Antioxidant Applications: Many chronic disease states and inflammatory conditions are a result of oxidative stress and subsequent generation of free radicals. Some of these include heart disease (resulting from LDL oxidation), renal disease and failure, several types of cancer, skin exposure damage caused by ultraviolet (A and B) rays, as well as diseases associated with aging. Green tea polyphenols are potent free radical scavengers due to the hydroxyl groups in their chemical structure. The hydroxyl groups can form complexes with free radicals and neutralize them, preventing the progression of the disease process.22
Obesity/Weight Control: Recent studies on green tea's thermogenic properties have demonstrated a synergistic interaction between caffeine and catechin polyphenols that appears to prolong sympathetic stimulation of thermogenesis. A human study of green tea extract containing 90 mg EGCG taken three times daily concluded that men taking the extract burned 266 more calories per day than did those in the placebo group and that green tea extract's thermogenic effects may play a role in controlling obesity.23 Green tea polyphenols have also beeen shown to markedly inhibit digestive lipases in vitro, resulting in decreased lipolysis of triglycerides, which may translate to reduced fat digestion in humans.10,11
Intestinal Dysbiosis and Infection: A small study in Japan demonstrated a special green tea catechin preparation (30.5% EGCG) was able to positively affect intestinal dysbiosis in nursing home patients by raising levels of Lactobacilli and Bifidobacteria while lowering levels of Enterobacteriaceae, Bacteroidaceae, and eubacteria. Levels of pathogenic bacterial metabolites were also decreased.12 An in vitro study also demonstrated green tea's antimicrobial activity against a variety of gram-positive and gram-negative pathogenic bacteria that cause cystitis, pyelonephritis, diarrhea, dental caries,24 pneumonia, and skin infections.13
Other Applications: Sickle cell anemia is characterized by a population of "dense cells" that may trigger vaso-occlusion and the painful sickle cell "crisis." One study demonstrated that 0.13 mg/mL green tea extract was capable of inhibiting dense-cell formation by 50 percent.25 Another potential therapeutic application of green tea is the treatment of psoriasis. The combination therapy of psoralens and ultraviolet A radiation is highly effective but has unfortunately been shown to substantially increase the risk for developing squamous cell carcinoma and melanoma. An in vitro study using human and mouse skin demonstrated that pre- and post-treatment with green tea extract inhibited DNA damage induced by the psoralen/ultraviolet A radiation exposure.8
Dosage and Toxicity Green tea is generally considered a safe, non-toxic beverage and consumption is usually without side-effects. The average cup of green tea, however, contains from 10-50 mg of caffeine and overconsumption may cause irritability, insomnia, nervousness, and tachycardia. Because studies on its possible teratogenic effect are inconclusive, caffeine consumption is contraindicated during pregnancy. Lactating women should also limit caffeine intake to avoid sleep disorders in infants.26 The dosage for green tea beverage varies, depending on the clinical situation and desired therapeutic effect. The phenolic content of green tea infusion is between 50-100 mg polyphenols per cup, depending on species, harvesting variables, and brewing methods,27 with typical dosages ranging from 3 to 10 cups per day. Cancer preventative effects are usually associated with dosages in the higher end of the range.28 Green tea extracts standardized to 80-percent total polyphenols are dosed at an average of 500-1500 mg per day.
References 1. Alschuler L. Grean Tea: Healing tonic. Am J Natur Med 1998;5:28-31. 2. Graham HN. Green tea composition, consumption, and polyphenol chemistry. Prev Med 1992;21:334-350. 3. Nihal A, Hasan M. Green tea polyphenols and cancer: biological mechanisms and practical implications. Nutr Rev 1999;57:78-83. 4. Ahmad N, Feyes DK, Nieminen AL, et al. Green tea constituent epigallacatechin-3-gallate and induction of apoptosis and cell cycle arrest in human carcinoma cells. J Natl Cancer Inst 1997;89:1881-1886. 5. Serafini M, Ghiselli A, Ferro-Luzzi A. In vivo antioxidant effect of green and black tea in man. Eur J Clin Nutr 1996;50:28-32. 6. Erba D, Riso P, Colombo A, Testolin G. Supplementation of Jurkat T cells with green tea extract decreases oxidative damage due to iron treatment. J Nutr 1999;129:2130-2134. 7. Katiyar SK, Matsui MS, Elmets CA, Mukhtar H. Polyphenolic antioxidant (-)-epigallocatechin-3-gallate from green tea reduces UVB-induced inflammatory responses and infiltration of leukocytes in human skin. Photochem Photobiol 1999;69:148-153. 8. Zhao JF, Zhang YJ, Jin XH, et al. Green tea protects against psoralen plus ultraviolet A-induced photochemical damage to skin. J Invest Dermatol 1999;113:1070-1075. 9. Hofbauer R, Frass M, Gmeiner B, et al. The green tea extract epigallocatechin gallate is able to reduce neutrophil transmigration through monolayers of endothelial cells. Wien Klin Wochenschr 1999;111:276-282. 10. Dulloo AG, Seydoux J, Girardier L, et al. Green tea and thermogenesis: interactions between catechin-polyphenols, caffeine, and sympathetic activity. Int J Obes Relat Metab Disord 2000;24:252-258. 11. J uhel C, Armand M, Pafumi Y, et al. Green tea extract (AR25) inhibits lipolysis of triglycerides in gastric and duodenal medium in vitro. J Nutr Biochem 2000;11:45-51. 12. Goto K, Kanaya S, Nishikawa T, et al. Green tea catechins improve gut flora. Ann Long-Term Care 1998;6:1-7. 13. Chou CC, Lin LL, Chung KT. Antimicrobial activity of tea as affected by the degree of fermentation and manufacturing season. Int J Food Microbiol 1999;48:125-130. 14. Katiyar SK, Mukhtar H. Tea antioxidants in cancer chemoprevention. J Cell Biochem 1997;27:S59-S67. 15. Lee IP, Kim YH, Kang MH, et al. Chemopreventative effect of green tea (Camellia sinensis) against cigarette smoke-induced mutations (SCE) in humans. J Cell Biochem 1997;27:S68-S75. 16. Picard D. The biochemistry of green tea polyphenols and their potential application in human skin cancer. Altern Med Rev 1996;1:31-42. 17. Hirose M, Hoshiya T, Akagi K, et al. Effects of green tea catechins in a rat multi-organ carcinogenesis model. Carcinogenesis 1993;14:1549-1553. 18. Sato D. Inhibition of urinary bladder tumors induced by N-butyl-N-(4-hydroxybutyl)-nitrosamine in rats by green tea. Int J Urol 1999;6:93-99. 19. Sugiyama T, Sadzuka Y. Enhancing effects of green tea components on the antitumor activity of adriamycin against M5076 ovarian sarcoma. Cancer Lett 1998;133:19-26. 20. Otsuka T, Ogo T, Eto T, et al. Growth inhibition of leukemic cells by (-)-epigallocatechin gallate, the main constituent of green tea. Life Sci 1998;63:1387-1403. 21. Khafif A, Schantz SP, al-Rawi M, et al. Green tea regulates cell cycle progression in oral leukoplakia. Head Neck 1998;20:528-534. 22. Ichihashi M, Ahmed NU, Budiyanto A, et al. Preventive effect of antioxidant on ultraviolet-induced skin cancer in mice. J Dermatol Sci 2000;23:S45-S50. 23. Dulloo AG, Duret C, Rohrer D, et al. Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. Am J Clin Nutrition 1999;70:1040-1045. 24. You S. Study on feasibility of Chinese green tea polyphenols (CTP) for preventing dental caries. Chung Hua Kou Hsueh Tsa Chih 1993;28:197-199. 25. Ohnishi ST, Ohnishi T, Ogunmola GB. Sickle cell anemia: a potential nutritional approach for a molecular disease. Nutrition 2000;16:330-338. 26. DerMarderosian A. The Review of Natural Products. St. Louis, MO: Facts and Comparisons, Wolters Kluwer Co. 1999. 27. Yamimoto T, Juneja LR, Djoing-Chu C, Kim M. Chemistry and Applications of Green Tea. Boca Raton, FL: CRC Press, 1997: 51-52, 28. Imai K, Suga K, Nakachi K. Cancer-preventative effects of drinking tea among a Japanese population. Prev Med 1997;26:769-775.
Tea and health: the underlying mechanisms. Weisburger JH. American Health Foundation, Valhalla, New York 10595, USA. John_Weisburger@nymc.edu Detailed multidisciplinary research on the effect of tea and the associated tea polyphenols has led to major advances on the underlying mechanisms. In most studies, green and black tea have similar effects, four of which are reviewed in this paper. 1) Tea polyphenols are powerful antioxidants that may play a role in lowering the oxidation of LDL-cholesterol, with a consequent decreased risk of heart disease, and also diminish the formation of oxidized metabolites of DNA, with an associated lower risk of specific types of cancer. 2) Tea and tea polyphenols selectively induce Phase I and Phase II metabolic enzymes that increase the formation and excretion of detoxified metabolites of carcinogens. 3) Tea lowers the rate of cell replication and thus the growth and development of neoplasms. 4) Tea modifies the intestinal microflora, reducing undesirable bacteria and increasing beneficial bacteria. The accumulated knowledge suggests that regular tea intake by humans might provide an approach to decrease the incidence of and mortality from major chronic diseases. Publication Types: Review Review, tutorial PMID: 10202402 [PubMed - indexed for MEDLINE]
10: Am J Clin Nutr 2000 Jun;71(6 Suppl):1698S-702S; discussion 1703S-4S Tea polyphenols: prevention of cancer and optimizing health. Mukhtar H, Ahmad N. Department of Dermatology, Case Western Reserve University, Cleveland, OH 44106, USA. hxm4@po.cwru.edu The tea plant Camellia sinesis is cultivated in >30 countries. Epidemiologic observations and laboratory studies have indicated that polyphenolic compounds present in tea may reduce the risk of a variety of illnesses, including cancer and coronary heart disease. Most studies involved green tea, however; only a few evaluated black tea. Results from studies in rats, mice, and hamsters showed that tea consumption protects against lung, forestomach, esophagus, duodenum, pancreas, liver, breast, colon, and skin cancers induced by chemical carcinogens. Other studies showed the preventive effect of green tea consumption against atherosclerosis and coronary heart disease, high blood cholesterol concentrations, and high blood pressure. Because the epidemiologic studies and research findings in laboratory animals have shown the chemopreventive potential of tea polyphenols in cancer, the usefulness of tea polyphenols for humans should be evaluated in clinical trials. One such phase 1 clinical trial is currently under way at the MD Anderson Cancer Center in collaboration with Memorial Sloan-Kettering Cancer Center. This study will examine the safety and possible efficacy of consuming the equivalent of > or =10 cups (> or =2.4 L) of green tea per day. The usefulness of tea polyphenols may be extended by combining them with other consumer products such as food items and vitamin supplements. This "designer-item" approach may be useful for human populations, but it requires further study. Publication Types: Review Review, tutorial PMID: 10837321 [PubMed - indexed for MEDLINE]
11: Nutr Cancer 1999;35(1):80-6 Chemopreventive effects of tea extracts and various components on human pancreatic and prostate tumor cells in vitro. Lyn-Cook BD, Rogers T, Yan Y, Blann EB, Kadlubar FF, Hammons GJ. Division of Molecular Epidemiology, National Center for Toxicological Research, Jefferson, AR 72079, USA. Pancreatic and prostate cancers pose serious problems to human health. To determine the potential for chemopreventive intervention against pancreatic and prostate cancers, black and green tea extracts and components of these extracts were examined in vitro for their effect on tumor cell growth. Components included a mixture of polyphenols from green tea (GTP), mixtures of polyphenols (BTP) and of theaflavins (MF) from black tea, and the purified components epicatechin-3-gallate (ECG) and epigallocatechin-3-gallate (EGCG). Two human cell lines, pancreatic adenocarcinoma (HPAC) and prostate tumor (LNCaP), were exposed to these agents for 24 hours. Results showed inhibition (approx 90%) of cell growth in pancreatic tumor cells by black and green tea extracts (0.02%). GTP (10 micrograms/ml) and MF (100 micrograms/ml) significantly inhibited growth (approx 90%); ECG and EGCG inhibited growth as well (approx 95%). Black and green tea extracts, GTP, and EGCG decreased the expression of the K-ras gene, as determined by reverse transcription-polymerase chain reaction. Green and black tea extracts decreased the multidrug-resistant gene (mdr-1), although GTP and EGCG increased expression. Similar data were obtained in the prostate cell line LNCaP. All agents significantly inhibited growth. These agents increased expression of the mdr-1 gene. This study suggests that components from black and green tea extracts can modulate the expression of genes known to play a role in the carcinogenesis process and, therefore, may be potential agents for chemoprevention against pancreatic cancer. PMID: 10624710 [PubMed - indexed for MEDLINE]
18: Proc Soc Exp Biol Med 1999 Apr;220(4):255-61 Antioxidant capacity and polyphenolic components of teas: implications for altering in vivo antioxidant status. Prior RL, Cao G. US Department of Agriculture, Agriculture Research Service, Jean Mayer Human Nutrition Research Center on Aging at Tufts University, Boston, Massachusetts 02111, USA.prior@hnrc.tufts.edu The Oxygen Radical Absorbance Capacity (ORAC) assay was used to determine the total antioxidant capacity of tea. Green and black teas (n = 18) had a mean antioxidant capacity of 761.1 +/- 85.3 micromol Trolox Equivalents (TE) per g dry matter. However, their antioxidant capacity varied from 235 micromol to over 1526 micromol Trolox equivalents (TE)/g dry matter, and total phenolics ranged from 32 to 147 mg/g in different commercial teas. One tea phenolics extract had an antioxidant capacity of 4796 micromol TE/g dry matter and 625 mg total phenolics/g. On a dry matter basis, an antioxidant capacity of 761 micromol TE/g is considerably higher than any of the other fruits and vegetables measured in our laboratory. However, since dry tea is not consumed directly, brewing conditions may influence the final antioxidant capacity in the tea as consumed. We tested both green and black teas by placing one tea bag (1.95 g) in 150 ml (5 oz.) of boiling water. In the first brewed cup, approximately 84% of the total antioxidant activity was solubilized within the first 5 min of brewing. An additional 13% of the antioxidant activity was extracted into the second glass of 150 ml with an additional 5 min of brewing. At the dilutions obtained after the first brewing, the tea as consumed would contain approximately 8. 31 micromol TE per ml. This total antioxidant capacity compares to other drinks from fruits and vegetables that had antioxidant capacity values ranging from 1.6 to 15 micromol TE/ml. At these antioxidant levels, consumption of 150 ml of tea could make a significant contribution to the total daily antioxidant capacity intake. (-)-Epicatechin and (+)-catechin, two components from tea, had an antioxidant capacity of 2.36 and 2.49 micromol/micromol or 8. 13 and 8.58 micromol/mg, respectively. In 16 tea samples we observed a mean of 10.0 +/- 0.6 micromol TE/mg total phenolics. Tea can be an important source of what has been referred to as "non-nutrient" antioxidant phytochemicals. However, with the variation that exists in antioxidant capacity with various tea preparations, measures of antioxidant capacity intake are critical to the study of intake and health outcomes and/or biomarkers of health outcomes. Publication Types: Review Review, tutorial PMID: 10202399 [PubMed - indexed for MEDLINE]
19: Proc Natl Acad Sci U S A 1999 Apr 13;96(8):4524-9 Prevention of collagen-induced arthritis in mice by a polyphenolic fraction from green tea. Haqqi TM, Anthony DD, Gupta S, Ahmad N, Lee MS, Kumar GK, Mukhtar H. Department of Medicine, Division of Rheumatic Diseases, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA. Identification of common dietary substances capable of affording protection or modulating the onset and severity of arthritis may have important human health implications. An antioxidant-rich polyphenolic fraction isolated from green tea (green tea polyphenols, GTPs) has been shown to possess anti-inflammatory and anticarcinogenic properties in experimental animals. In this study we determined the effect of oral consumption of GTP on collagen-induced arthritis in mice. In three independent experiments mice given GTP in water exhibited significantly reduced incidence of arthritis (33% to 50%) as compared with mice not given GTP in water (84% to 100%). The arthritis index also was significantly lower in GTP-fed animals. Western blot analysis showed a marked reduction in the expression of inflammatory mediators such as cyclooxygenase 2, IFN-gamma, and tumor necrosis factor alpha in arthritic joints of GTP-fed mice. Histologic and immunohistochemical analysis of the arthritic joints in GTP-fed mice demonstrated only marginal joint infiltration by IFN-gamma and tumor necrosis factor alpha-producing cells as opposed to massive cellular infiltration and fully developed pannus in arthritic joints of non-GTP-fed mice. The neutral endopeptidase activity was approximately 7-fold higher in arthritic joints of non-GTP-fed mice in comparison to nonarthritic joints of unimmunized mice whereas it was only 2-fold higher in the arthritic joints of GTP-fed mice. Additionally, total IgG and type II collagen-specific IgG levels were lower in serum and arthritic joints of GTP-fed mice. Taken together our studies suggest that a polyphenolic fraction from green tea that is rich in antioxidants may be useful in the prevention of onset and severity of arthritis. PMID: 10200295 [PubMed - indexed for MEDLINE]
1: Mutat Res 2001 Aug 22;495(1-2):61-74 Potent antimutagenic activity of white tea in comparison with green tea in the Salmonella assay. Santana-Rios G, Orner GA, Amantana A, Provost C, Wu S, Dashwood RH. Linus Pauling Institute, Department of Environmental and Molecular Toxicology, Oregon State University, 571 Weniger Hall, 97331-6512, Corvallis, OR, USA There is growing interest in the potential health benefits of tea, including the antimutagenic properties. Four varieties of white tea, which represent the least processed form of tea, were shown to have marked antimutagenic activity in the Salmonella assay, particularly in the presence of S9. The most active of these teas, Exotica China white tea, was significantly more effective than Premium green tea (Dragonwell special grade) against 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and four other heterocyclic amine mutagens, namely 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethyl-3H-imidazo[4,5-f]quinoxaline (4,8-DiMeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2). Mechanism studies were performed using rat liver S9 in assays for methoxyresorufin O-demethylase (MROD), a marker for the enzyme cytochrome P4501A2 that activates heterocyclic amines, as well as Salmonella assays with the direct-acting mutagen 2-hydroxyamino-3-methylimidazo[4,5-f]quinoline (N-hydroxy-IQ). White tea at low concentrations in the assay inhibited MROD activity, and attenuated the mutagenic activity of N-hydroxy-IQ in the absence of S9. Nine of the major constituents found in green tea also were detected in white tea, including high levels of epigallocatechin-3-gallate (EGCG) and several other polyphenols. When these major constituents were mixed to produce 'artificial' teas, according to their relative levels in white and green teas, the complete tea exhibited higher antimutagenic potency compared with the corresponding artificial tea. The results suggest that the greater inhibitory potency of white versus green tea in the Salmonella assay might be related to the relative levels of the nine major constituents, perhaps acting synergistically with other (minor) constituents, to inhibit mutagen activation as well as 'scavenging' the reactive intermediate(s). PMID: 11448643 [PubMed - in process]
2: J Nutr Biochem 2001 Jul;12(7):404-421 A review of latest research findings on the health promotion properties of tea. Dufresne CJ, Farnworth ER. Food Research and Development Centre, Agriculture and Agri-food Canada, 3600 Casavant Boulevard West, J2S 8E3, Saint Hyacinthe, Quebec, Canada Important progress has been made in the past five years concerning the effects of green and black tea on health. Experimentation with new accurate tools provide useful information about the metabolism of tea components in the body, their mode of action as antioxidants at the cellular level and their protective role in the development of cancer, cardiovascular disease and other pathologies. The use of tea components as nutraceuticals and functional foods are also discussed. PMID: 11448616 [PubMed - as supplied by publisher]
3: QJM 2001 May;94(5):277-82 Tea flavonoids and cardiovascular health. Riemersma RA, Rice-Evans CA, Tyrrell RM, Clifford MN, Lean ME. Cardiovascular Research Unit, University of Edinburgh, UK. rudolph.riemersma@ed.ac.uk Tea is rich in antioxidant polyphenols (catechins, flavonols, theaflavins and thearubigins). Epidemiological evidence relating regular consumption of tea or related polyphenols to CHD is equivocal. Catechins are absorbed from tea, but low plasma concentrations are attained. The bioavailability of theaflavins and thearubigins is unknown. Tea does not reduce blood pressure or plasma lipids in well-controlled human trials. Tea polyphenols inhibit LDL lipid peroxidation in vitro, but the effect ex vivo is small. The plasma antioxidant potential increases after drinking green but not black tea. Tea consumption tended to reduce the development of aortic atherosclerosis in rabbits. Tea polyphenols exert marked effects on cells, and inhibit neutrophil migration and inflammatory responses, sometimes at low concentrations. These diverging results suggest potential beneficial effects, but emphasize the need for good human trials of tea using early markers of CHD before firm conclusions can be drawn. Publication Types: Review Review, academic PMID: 11353103 [PubMed - indexed for MEDLINE]
4: J Med Microbiol 2001 Apr;50(4):299-302 Anti-cariogenic properties of tea (Camellia sinensis). Hamilton-Miller JM. Department of Medical Microbiology, Royal Free and University College Medical School, London. j.hamilton-miller@rfc.ucl.ac.uk Various components in green and black tea, the beverages made by infusing appropriately processed dried leaves of Camellia sinensis, notably simple catechins, have properties in vitro that suggest an anti-cariogenic activity. These include: a direct bactericidal effect against Streptococcus mutans and S. sobrinus; prevention of bacterial adherence to teeth; inhibition of glucosyl transferase, thus limiting the biosynthesis of sticky glucan; inhibition of human and bacterial amylases. Studies in animal models show that these in-vitro effects can translate into caries prevention. A limited number of clinical trials in man suggest that regular tea drinking may reduce the incidence and severity of caries. If substantiated, this could offer a very economical public health intervention. Publication Types: Review Review, tutorial PMID: 11289514 [PubMed - indexed for MEDLINE]
5: N Engl J Med 2001 Mar 1;344(9):632-6 Comment in: N Engl J Med. 2001 Mar 1;344(9):675-6 Green tea and the risk of gastric cancer in Japan. Tsubono Y, Nishino Y, Komatsu S, Hsieh CC, Kanemura S, Tsuji I, Nakatsuka H, Fukao A, Satoh H, Hisamichi S. Department of Public Health and Forensic Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan. ytsubono@metamedica.com BACKGROUND: Although laboratory experiments and case-control studies have suggested that the consumption of green tea provides protection against gastric cancer, few prospective studies have been performed. METHODS: In January 1984, a total of 26,311 residents in three municipalities of Miyagi Prefecture, in northern Japan (11,902 men and 14,409 women 40 years of age or older), completed a self-administered questionnaire that included questions about the frequency of consumption of green tea. During 199,748 person-years of follow-up, through December 1992, we identified 419 cases of gastric cancer (in 296 men and 123 women). We used Cox regression to estimate the relative risk of gastric cancer according to the consumption of green tea. RESULTS: Green-tea consumption was not associated with the risk of gastric cancer. After adjustment for sex, age, presence or absence of a history of peptic ulcer smoking status, alcohol consumption, other dietary elements, and type of health insurance, the relative risks associated with drinking one or two, three or four, and five or more cups of green tea per day, as compared with less than one cup per day, were 1.1 (95 percent confidence interval, 0.8 to 1.6), 1.0 (95 percent confidence interval, 0.7 to 1.4), and 1.2 (95 percent confidence interval, 0.9 to 1.6), respectively (P for trend=0.13). The results were similar after the 117 cases of gastric cancer that were diagnosed in the first three years of follow-up had been excluded, with respective relative risks of 1.2 (95 percent confidence interval, 0.8 to 1.8) 1.0 (95 percent confidence interval, 0.7 to 1.5), and 1.4 (95 percent confidence interval, 1.0 to 1.9) (P for trend=0.07). CONCLUSIONS: In a population-based, prospective cohort study in Japan, we found no association between green-tea consumption and the risk of gastric cancer. PMID: 11228277 [PubMed - indexed for MEDLINE]
6: Biofactors 2000;12(1-4):45-51 Role of diet modification in cancer prevention. Abdulla M, Gruber P. Trace Element-Institute for UNESCO, Lyon, France. Carcinogenesis encompasses a prolonged accumulation of injuries at several different biological levels and include both genetic and biochemical changes in the cells. At each of these levels, there are several possibilities of intervention in order to prevent, slow down or even halt the gradual march of healthy cells towards malignancy. Diet modification is one such possibility. A number of natural foodstuffs, especially fruits and vegetables contain substantial quantities of molecules that have chemopreventive potential against cancer development. Such compounds include vitamins, trace elements and a variety of other molecules with antioxidant properties. Carotenoids, flavanoid polyphenols, isoflavones, catechins, and several other components that found in cruciferous vegetables are molecules that are known to protect against the deleterious effect of reactive oxygen species. A number of epidemiological and experimental studies have shown that vitamin C and E, Beta-carotene and the essential trace element selenium can reduce the risk of cancer. Consistent observations during the last few decades that cancer risk is reduced by a diet rich in vegetables, fruits, legumes, grains and green tea have encouraged research to identify several plant components especially phytochemicals that protect against DNA damage. Many of these substances block specific carcinogen pathways. Dietary supplements are part of an overall health program, along with a high intake of fruits and vegetables that help to combat damage to cells, which in turn may initiate cancer development. This paper will review current knowledge concerning diet modification and cancer prevention with special reference to minerals and trace elements. Publication Types: Review Review, tutorial PMID: 11216504 [PubMed - indexed for MEDLINE]
7: J Toxicol Sci 2000 Aug;25(3):199-204 Protective effects of (-)-epigallocatechin gallate and (+)-catechin on paraquat-induced genotoxicity in cultured cells. Tanaka R. Akita Keijo Junior College, Japan. The protective effects of green tea polyphenols on paraquat-induced genotoxicity in cultured cells were studied. (-)-Epigallocatechin gallate (EGCG), the major constituent of green tea, and (+)-catechin (CT), a minor constituent, equivalently decreased the frequencies of sister-chromatid exchanges (SCE) induced by paraquat (PQ), which is a generator of reactive oxygen species. These polyphenols were effective at concentrations of 1.0 microM and above. A reduction of the effect on the cell cycle rate caused by PQ was found when EGCG and CT were added at concentrations of more than 10.0 microM. These concentrations of EGCG and CT alone had no effect on cell cycle rate, which is used as index of cell proliferation. Decreases in the cell cycle rate were found at 200 microM EGCG and CT in the 24 hr exposure period. The equivalent effectiveness of EGCG and CT suggested the possibility of other mechanisms, apart from acting as reactive oxygen species scavengers, because it has been reported that EGCG is the most potent scavenger among tea catechins. From the present study, it was suggested that green tea and foods containing these polyphenols may be beneficial to human health by protecting against reactive oxygen species-induced genotoxicity. PMID: 10987127 [PubMed - indexed for MEDLINE]
8: Int J Food Sci Nutr 2000 May;51(3):181-8 Antioxidant potential of green and black tea determined using the ferric reducing power (FRAP) assay. Langley-Evans SC. University College Northampton, UK. Tea is one of the most commonly consumed beverages in the world and is rich in polyphenolic compounds collectively known as the tea flavonoids. Tea flavonoids possess antioxidant properties in vitro and have been proposed as key protective dietary components, reducing risk of coronary heart disease and some cancers. The present study aimed to evaluate the possible effects of different preparation methods on the antioxidant properties of green and black tea. Antioxidant potentials of tea infusates were assessed using an assay based upon the reduction of ferric chloride linked to a chromophore. Green tea, black leaf tea and black tea in tea bags were infused with water at 90 degrees C for time periods ranging from 0.25 to 15 min. Green tea infusates possessed approximately 2.5-fold greater antioxidant capacity than both types of black tea infusates. Both green and black teas released significant levels of antioxidants into the hot water within 2 min of infusion. Preparation of teas across a range of temperatures between 20 and 90 degrees C revealed that although antioxidants were liberated from the leaves into the water in cooler infusions, increasing the temperature could increase antioxidant potential by 4 to 9.5-fold. Black tea prepared using tea bags had significantly lower antioxidant capacity than black leaf tea at temperatures between 20 and 70 degrees C, suggesting that tea bag materials may prevent some extraction of flavonoids into the tea solution. The addition of milk appeared to diminish the antioxidant potential of black tea preparations. This effect was greatest where whole cow's milk was used and appeared to be primarily related to the fat content of the added milk. These experiments have considered the effects of commonly used domestic methods of preparation on the in vitro antioxidant potential of tea. It is concluded that maximum antioxidant capacity and hence maximal health benefit may be derived from green tea or from black leaf tea prepared by infusion with water at 90 degrees C for up to 2 min and taken with the addition of either fat-free milk, or without milk addition. Further studies are required to assess the antioxidant actions of tea flavonoids in vivo. PMID: 10945114 [PubMed - indexed for MEDLINE]
9: Am J Clin Nutr 2000 Jun;71(6 Suppl):1710S-4S; discussion 1715S-9S Approaches for chronic disease prevention based on current understanding of underlying mechanisms. Weisburger JH. American Health Foundation, Valhalla, NY 10595-1599, USA. john_weisburger@nymc.edu Much progress has been achieved by exploring the causes of the main human cancers and of cardiovascular and cerebrovascular diseases. Even more important has been the knowledge acquired about the mechanisms underlying the development of these diseases. In many parts of the world, particularly in the West, the major cancers associated with dietary habits involve the postmenopausal breast, distal colon, prostate, pancreas, ovary, and endometrium. Current evidence suggests that the genotoxic carcinogens for all but the last 2 of these diseases stem from the traditional intake of fried and broiled foods such as meats. The surface of these foods contains a class of powerful mutagens, heterocyclic amines, which are carcinogenic to the target organs in animal models. Fish-eating populations have lower incidences of heart disease and of many types of cancers than do other populations, which may be the result of the n-3 polyunsaturated oils found in fish. Among other dietary practices that may reduce the risk of cancer and cardiovascular disease are consuming 5-9 servings of fruits and vegetables daily, which provides antioxidants such as quercetin and isothiocyanates; having a high fiber intake, including bran cereal; and drinking 1.5-2.5 L of fluids daily. Tea polyphenols found in black and green tea may have a protective effect against heart disease and some cancers. Concentrates of such desirable products have been made available in pill form to complement health-promoting personal lifestyles. Biomedical research funded by The National Institutes of Health and organizations such as the American Cancer Society has produced sound results that could lead to prevention of chronic disease. The public must heed this information to achieve long-term health. Publication Types: Review Review, tutorial PMID: 10837325 [PubMed - indexed for MEDLINE]
12: Ren Fail 1999 Nov;21(6):581-91 Antioxidants in the prevention of renal disease. Wardle EN. In view of the role of oxidative processes in inflicting damage that leads to glomerulosclerosis and renal medullary interstitial fibrosis, more attention could be paid to the use of antioxidant food constituents and the usage of drugs with recognized antioxidant potential. In any case atherosclerosis is an important component of chronic renal diseases. There is a wide choice of foods and drugs that could confer benefit. Supplementation with vitamins E and C, use of soy protein diets and drinking green tea could be sufficient to confer remarkable improvements. Publication Types: Review Review, tutorial PMID: 10586421 [PubMed - indexed for MEDLINE]
13: Nutrition 1999 Nov-Dec;15(11-12):946-9 Tea and health. Yang CS. The possible beneficial effects of tea consumption in the prevention of cancer and cardiovascular diseases have been demonstrated in animal models and suggested by studies in vitro. Similar beneficial effects, however, have not been convincingly demonstrated in humans: beneficial effects have been demonstrated in some studies but not in others. If such beneficial effects do exist in humans, they are likely to be mild, depending on many other lifestyle-related factors, and could be masked by confounding factors in certain populations. Another concern is that the amounts of tea consumed by humans are lower than the doses required for demonstrating the disease-prevention effects in animal models. Caution should be applied, however, in the use of high concentrations of tea for disease prevention. Ingestion of large amounts of tea may cause nutritional and other problems because of the caffeine content and the strong binding activities of tea polyphenols, although there are no solid data on the harmful effects of tea consumption. More research is needed to elucidate the biologic activities of green and black tea and to determine the optimal amount of tea consumption for possible health-beneficial effects. Publication Types: Editorial Review Review, tutorial PMID: 10575676 [PubMed - indexed for MEDLINE]
14: Food Chem Toxicol 1999 Sep-Oct;37(9-10):943-8 Mechanisms of action of antioxidants as exemplified in vegetables, tomatoes and tea. Weisburger JH. American Health Foundation, Valhalla, NY 10585, USA. Most chronic diseases, including coronary heart disease and many types of cancer depend on the in vivo conversion of cellular macromolecules or of carcinogens to specific reactive, oxidized forms. For that reason, health promoting nutrition involves the daily intake of five to 10 vegetables and fruits, fruit juices, red wine and tea that are rich sources of micronutrients with antioxidant properties, including the antioxidant vitamins C, E and beta-carotene. Tomatoes contain lycopene, a stable, active antioxidant. Many vegetables contain quercetin and related polyphenolic compounds. Tea is a source of epigallocatechin gallate, in green tea, and theaflavin and the associated thearubigins, in black tea. Red wine contains resveratrol. The diverse antioxidants in foods, red wine and tea provide the necessary antioxidant resources for the body to control oxidation reactions in the body with possible adverse consequences. For example, the oxidation of low density lipoprotein (LDL) cholesterol yields a product that damages the vascular system. Thus, a lower intake of saturated fats to decrease the levels of LDL cholesterol, together with an adequate intake of antioxidants, is the optimal approach to lower heart disease risk. Cancer of the stomach involves the consumption of salted, pickled foods yielding direct-acting carcinogens, and their formation is inhibited by vitamins C and E. Cancer in the colon, breast, prostate and pancreas may be caused by a new class of carcinogens, the heterocyclic amines, formed during the broiling or frying of creatinine-containing foods, including fish and meats. Their formation and action can be inhibited by antioxidants such as those in soy, tea, vitamin C and also by the synthetic antioxidants BHA or BHT. The growth, cell proliferation and development of abnormal preneoplastic and neoplastic cells also involves oxidation reactions, including the formation of active oxygen or peroxy compounds. Such reactions can be inhibited by antioxidants, such as those in tea, tomatoes or vegetables. Even ageing and longevity in good health would be favoured by the availability of adequate amounts of varied antioxidants. Prevention of the formation and of action of reactive products by antioxidants as present in fruits, vegetables, tomatoes, red wine and tea is of great public health importance in decreasing the risk of major diseases. Prevention is the optimal approach to disease control, and also as an effective route to lower costs of medical care. Publication Types: Review Review, tutorial PMID: 10541449 [PubMed - indexed for MEDLINE]
15: Am J Clin Nutr 1999 Sep;70(3 Suppl):491S-499S Health-promoting properties of common herbs. Craig WJ. Department of Nutrition, Andrews University, Berrien Springs, MI 49104-0210, USA. wcraig@andrews.edu Herbs have been used as food and for medicinal purposes for centuries. Research interest has focused on various herbs that possess hypolipidemic, antiplatelet, antitumor, or immune-stimulating properties that may be useful adjuncts in helping reduce the risk of cardiovascular disease and cancer. In different herbs, a wide variety of active phytochemicals, including the flavonoids, terpenoids, lignans, sulfides, polyphenolics, carotenoids, coumarins, saponins, plant sterols, curcumins, and phthalides have been identified. Several of these phytochemicals either inhibit nitrosation or the formation of DNA adducts or stimulate the activity of protective enzymes such as the Phase II enzyme glutathione transferase (EC 2.5.1.18). Research has centered around the biochemical activity of the Allium sp. and the Labiatae, Umbelliferae, and Zingiberaceae families, as well as flaxseed, licorice root, and green tea. Many of these herbs contain potent antioxidant compounds that provide significant protection against chronic diseases. These compounds may protect LDL cholesterol from oxidation, inhibit cyclooxygenase and lipoxygenase enzymes, inhibit lipid peroxidation, or have antiviral or antitumor activity. The volatile essential oils of commonly used culinary herbs, spices, and herbal teas inhibit mevalonate synthesis and thereby suppress cholesterol synthesis and tumor growth. Publication Types: Review Review, tutorial PMID: 10479221 [PubMed - indexed for MEDLINE]
16: Proc Soc Exp Biol Med 1999 Apr;220(4):249-54 The effect of tea consumption on oxidative stress in smokers and nonsmokers. Klaunig JE, Xu Y, Han C, Kamendulis LM, Chen J, Heiser C, Gordon MS, Mohler ER 3rd. Indiana University School of Medicine, Indianapolis, Indiana 46202, USA. While the anticarcinogenic effects of tea in animal models have been reported by several groups, human epidemiological studies examining tea consumption and cancer prevention have produced equivocal results. The beneficial properties of tea to human health may be related to the antioxidant properties of tea components. However, little evidence has been provided that tea consumption can either increase the antioxidant capacity or decrease oxidative stress in humans. In the present study, the effects of tea treatment (green tea) on biomarkers of oxidative stress were investigated in smokers and nonsmokers in two volunteer study groups (one in China and the other in United States). Green tea consumption in both study groups decreased oxidative DNA damage (8-OHdG in white blood cells and urine), lipid peroxidation (MDA in urine), and free radical generation (2, 3-DHBA in urine) in smokers. Nonsmokers (US study group) also exhibited a decrease in overall oxidative stress. PMID: 10202398 [PubMed - indexed for MEDLINE]
17: Proc Soc Exp Biol Med 1999 20: Mutat Res 1998 Jun 18;402(1-2):331-7 Worldwide prevention of cancer and other chronic diseases based on knowledge of mechanisms. Weisburger JH. American Health Foundation, Valhalla, NY 10595, USA. john_weisburger@nymc.edu International research, particularly as part of US/Japan programs, has led to major advances in knowledge of causes of heart disease, stroke, many types of cancer and diabetes, showing that individual lifestyle is associated with these diseases. In Japan, a major health problem is high blood pressure and stroke, and cancer of the stomach, from excessive use of salt and salted, pickled foods, and the relative low intake of protective fruits and vegetables. We identified a likely gastric carcinogen, 2-chloro-4-methylthiobutanoate, in salted, pickled fish. In the Western world, heart disease and cancer of the breast, colon, rectum, prostate, pancreas, ovary and endometrium relate to a nutritional tradition too high in total fat and fried or broiled meats, and too low in fiber, vegetables and fruits. The cooked meats contain genotoxic chemicals, heterocyclic amines, causative elements in heart disease and the nutritionally linked cancers. Decreasing total fat intake, from 40 to 20% of calories and a greater use of starches such as rice, pasta, potatoes and whole grain bread, as well as daily intake of five to nine vegetables and fruits would be beneficial. Adults should consume 2.5 l of fluids per day. Green or black tea and fruit juices have health promoting properties. Regular exercise contributes to good health, and to the avoidance of obesity, a major problem in the USA and of increasing importance in Japan. Avoidance of a risky lifestyle would likely prevent diseases important not only for the individual and his family, but with major impact in lowering medical care costs. Tobacco and cigarette use, particularly on a Western diet, involve a high risk of heart attacks, and cancers of the lung, pancreas, kidney, urinary bladder, and cervix, accounting for 35% of medical care expenditures. Copyright 1998 Elsevier Science B.V. All rights reserved. Publication Types: Review Review, tutorial PMID: 9675332 [PubMed - indexed for MEDLINE]
21: Prev Med 1997 Nov-Dec;26(6):769-75 Cancer-preventive effects of drinking green tea among a Japanese population. Imai K, Suga K, Nakachi K. Department of Epidemiology, Saitama Cancer Center Research Institute, Japan. BACKGROUND: Laboratory studies have revealed the cancer preventive effects of green tea, so the association between green tea consumption and cancer was examined in a human population. METHODS: The association between green tea consumption and cancer incidence was studied in our prospective cohort study of a Japanese population. We surveyed 8,552 individuals over 40 years of age living in a town in Saitama prefecture on their living habits, including daily consumption of green tea. During the 9 years of follow-up study (71,248.5 person-years), we identified a total of 384 cases of cancer in all sites. RESULTS: We found a negative association between green tea consumption and cancer incidence, especially among females drinking more than 10 cups a day. The slowdown in increase of cancer incidence with age observed among females who consumed more than 10 cups a day is consistent with the finding that increased consumption of green tea is associated with later onset of cancer. Age-standardized average annual incidence rate was significantly lower among females who consumed large amounts of green tea. Relative risk (RR) of cancer incidence was also lower among both females (RR = 0.57, 95% CI = 0.33-0.98) and males (RR = 0.68, 95% CI = 0.39-1.21) in groups with the highest consumption, although the preventive effects did not achieve statistical significance among males, even when stratified by smoking and adjusted for alcohol and dietary variables. CONCLUSION: Our epidemiological study showed that green tea has a potentially preventive effect against cancer among humans. PMID: 9388788 [PubMed - indexed for MEDLINE]
22: Cancer Lett 1997 Mar 19;114(1-2):315-7 Tea and health: a historical perspective. Weisburger JH. American Health Foundation, Valhalla, NY 10595-1599, USA. johnweisburger@nymc.edu In many parts of the world, green tea and black tea are produced from the plant Camellia sinensis. Tea is one of the most widely consumed beverages, second only to water. It is one of the safest beverages since it is made with boiling, sterile water and has been popular for over 4000 years. Dogma has it that people knew it might have health promoting properties since it was frequently used as fluid supply for patients suffering from infectious diseases. However, detailed, focused research on the health benefits of tea is of recent vintage. Initially, such research was carried out in Japan and China and, because the local customs, this research involved green tea. Now, a number of other scientists in Europe and in the United States have conducted investigations on black tea, and in some laboratories exacting comparative studies were performed utilizing black and green tea. The major interest in tea and health stems from the high level of antioxidant tea polyphenols in green tea and black tea. The chemistry of the tea polyphenols has been worked out to some extent. Thus, their role in lowering the risk of heart disease and of a number of types of cancer begins to be understood. Most productive are multi-disciplinary approaches, considering data from epidemiology and field studies, and laboratory research in animal models for heart disease and cancers of various types, as well as through in vitro experiments. Publication Types: Historical article PMID: 9103320 [PubMed - indexed for MEDLINE]