Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Tea”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19Linked to original sources
PubMed2002

[Cancer prevention with green tea: reality and wishful thinking].

Different processing of the leaves of the tea plant Camellia sinensis yields green or black tea, the subject of numerous investigations on the preventive effects on chronic degenerative diseases. The tea polyphenols, in particular (-)-epigallocatechin gallate (EGCG) were found to account for most of the protective effects. Since the concentration of EGCG is 5 times higher in green than in black tea, it is assumed that green tea possesses a greater preventive potential. Protection against cancer and cardiovascular diseases are the most important biomedical effects. In experimental models the preventive activity of tea is well documented for tumors at many organ sites. In humans, tea was reported to be protective against tumors of the lung, the gastrointestinal tract and the liver. Tea polyphenols, especially EGCG, were shown to exert cancer-protective activity by the following mechanisms: they inhibit the metabolic activation of carcinogens and induce at the same time detoxifying enzymes. They inhibit signaling pathways controlling cell proliferation and tumor growth such as protein kinase C and the release of tumor necrose factor-alpha from cells. Tea polyphenols reactivate processes which are impaired in tumor cells, such as the programmed cell death and the tumorsuppressor gene p53. Finally, tea polyphenols can also block angiogenesis leading to a starvation of the tumor. By inactivation of proteolytic enzymes they inhibit the development of metastases. This short review summarizes relevant recent findings on the protective effects of green tea constituents.

Animals↗
PubMed2002

Acute effects of ingestion of black tea on postprandial platelet aggregation in human subjects.

Results of population studies suggest that black tea can reduce cardiovascular risk. Effects of black-tea polyphenols to reduce platelet aggregability may help to explain any benefits. Given that black tea is often consumed with and after meals, and man spends much of his life in the postprandial state, the objective of the present study was to investigate the acute effects of ingestion of black tea on postprandial platelet aggregation ex vivo. Twenty healthy participants had platelet aggregation and blood lipids assessed before and 4 h after the ingestion of 50 g dairy fat on two occasions in random order, corresponding to black tea or hot water. Black tea or hot water (one cup) was consumed immediately following the dairy fat, then after 15 and 30 h. Platelet aggregation ex vivo was assessed in platelet-rich plasma in response to three concentrations of collagen (0.2, 0.6, 20 microg/ml) and ADP (2, 4, 8 microM). Urinary concentrations of 4-O-methylgallic acid were used as an indicator that tea polyphenols were absorbed. Serum total cholesterol and triacylglycerol concentrations increased significantly 4 h after ingesting the dairy fat, but there was no significant difference between black tea and hot-water treatments on the cholesterol or triacylglycerol responses. Urinary 4-O-methylgallic acid concentrations were significantly increased following ingestion of black tea (P=0.0001) but not water. Black tea in comparison to hot water did not inhibit collagen or ADP-induced postprandial platelet aggregation. The results of this study do not support the suggestion that reduced postprandial platelet aggregability contributes to any benefits of black tea on cardiovascular risk.

Adenosine Diphosphate↗
PubMed2002

Tea consumption and the reduced risk of colon cancer -- results from a national prospective cohort study.

OBJECTIVE: This study examines the relationship between tea consumption and colon cancer risk in the US population. DESIGN: Data from the NHANES I Epidemiologic Follow-up study (NHEFS) were used to examine the hypothesis. Cox proportional hazard models were used to examine the hypothesis of a protective effect of frequent tea consumption on colon cancer occurrence. SETTING: Due to differences in the precision of the exposure data, we analysed two cohort periods based on the NHEFS. Cohort I was based on the survey conducted at the NHEFS baseline and Cohort II began at the first follow-up. SUBJECTS: After excluding non-incidence cases and cases lost to follow-ups, there were 2359 tea users and 6498 non-tea users at baseline and 7656 tea users and 4514 non-tea users at the first follow-up. RESULTS: : After adjusting for confounders, the relative risks of colon cancer are 0.57 (95% confidence interval (CI) 0.42, 0.78) and 0.59 (95% 1.00) for subjects who consumed 1.5 cups per day, respectively, compared with non-tea users in Cohort II. Although more women consumed tea and the mean intake was higher, the preventive effect of tea consumption on colon cancer was found predominantly in men. The relative risks of colon cancer are 0.41 (95% 0.66) for men who consumed 1.5 cups day-1 of tea consumption (P-value for trend <0.01). No significant results were found in Cohort I. CONCLUSIONS: This study suggests an inverse association between colon cancer risk and habitual tea consumption.

Adult↗
PubMed1997

Tea and cancer prevention: an evaluation of the epidemiologic literature.

Animal and in vitro studies provide evidence of an anticarcinogenic potential of active ingredients in teas. This review encompasses epidemiologic 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 epidemiologic 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 categorization of tea consumption, choice of control groups, and inadequate control for confounding might have obscured possible relationships. From the limited studies that suggest a favorable effect from tea, it is likely that benefits are restricted to high intakes in high-risk populations.

Antineoplastic Agents↗
PubMed2006

Beneficial effects of green tea--a review.

Tea is the most consumed drink in the world after water. Green tea is a 'non-fermented' tea, and contains more catechins, than black tea or oolong tea. Catechins are in vitro and in vivo strong antioxidants. In addition, its content of certain minerals and vitamins increases the antioxidant potential of this type of tea. Since ancient times, green tea has been considered by the traditional Chinese medicine as a healthful beverage. Recent human studies suggest that green tea may contribute to a reduction in the risk of cardiovascular disease and some forms of cancer, as well as to the promotion of oral health and other physiological functions such as anti-hypertensive effect, body weight control, antibacterial and antivirasic activity, solar ultraviolet protection, bone mineral density increase, anti-fibrotic properties, and neuroprotective power. Increasing interest in its health benefits has led to the inclusion of green tea in the group of beverages with functional properties. However, although all the evidence from research on green tea is very promising, future studies are necessary to fully understand its contributions to human health, and advise its regular consumption in Western diets, in which green tea consumption is nowadays limited and sporadic.

Anticarcinogenic Agents↗
PubMed2005

Green tea intake, ACE gene polymorphism and breast cancer risk among Chinese women in Singapore.

Experimental and epidemiological data have implicated a potential chemoprotective role of green tea polyphenols and a potential enhancing role of angiotensin II in the development of breast cancer in humans. Angiotensin II is converted from its precursor by angiotensin-converting enzyme (ACE). Women with low-activity genotype of the ACE gene had a reduced risk of breast cancer compared with those possessing high-activity ACE genotype. Experimental data showed that green tea polyphenols could inhibit angiotensin II-induced reactive oxygen species production. We reasoned that if this is one of the mechanisms by which green tea polyphenols protect against human breast cancer, then their effect should be more prominent among women possessing high-activity ACE genotype than women with low-activity ACE genotype. In other words, we predict a stronger inverse green tea-breast cancer association among the former versus the latter subgroup of women. To test this hypothesis, we conducted a nested case-control study involving 297 incident breast cancer cases and 665 control subjects within the Singapore Chinese Health Study. There was no association between intake frequencies of green tea and risk of breast cancer among all women or those with low-activity ACE genotype. Among women with high-activity ACE genotype, however, intake frequency of green tea was associated with a statistically significant decrease in risk of breast cancer (P for trend=0.039); the odds ratio (95% confidence interval) was 0.33 (0.13-0.82) for women drinking green tea at least monthly and 0.29 (0.10-0.79) for those drinking green tea at least weekly compared with non-drinkers. There was a statistically significant interaction effect between green tea intake and ACE genotype on risk of breast cancer (P for interaction=0.01). Black tea intake was unrelated to breast cancer risk irrespective of the ACE genotype. The findings of the present study highlight the importance of genetically determined factors in evaluating the role of green tea intake in the development of breast cancer.

Adult↗
PubMed2007

Addition of milk prevents vascular protective effects of tea.

AIMS: Experimental and clinical studies indicate that tea exerts protection against cardiovascular diseases. However, a question of much debate is whether addition of milk modifies the biological activities of tea. We studied the vascular effects of tea, with or without milk, in humans and elucidated the impact of individual milk proteins in cell culture experiments, with isolated rat aortic rings and by HPLC analysis. METHODS AND RESULTS: A total of 16 healthy female volunteers consumed either 500 mL of freshly brewed black tea, black tea with 10% skimmed milk, or boiled water as control. Flow-mediated dilation (FMD) was measured by high-resolution vascular ultrasound before and 2 h after consumption. Black tea significantly improved FMD in humans compared with water, whereas addition of milk completely blunted the effects of tea. To support these findings, similar experiments were performed in isolated rat aortic rings and endothelial cells. Tea induced vasorelaxation in rat aortic rings and increased the activity of endothelial nitric oxide synthase by phosphorylation of the enzyme in endothelial cells. All effects were completely inhibited by the addition of milk to tea. Of the various kinds of milk proteins, the caseins accounted for these inhibiting effects of milk, probably by formation of complexes with tea catechins. CONCLUSION: Milk counteracts the favourable health effects of tea on vascular function. This finding indicates the need for particular awareness in the interpretation and design of studies comprising nutritional flavonoids.

Animals↗
PubMed2001

Oolong tea increases metabolic rate and fat oxidation in men.

According to traditional Chinese belief, oolong tea is effective in the control of body weight. Few controlled studies, however, have been conducted to measure the impact of tea on energy expenditure (EE) of humans. A randomized cross-over design was used to compare 24-h EE of 12 men consuming each of four treatments: 1) water, 2) full-strength tea (daily allotment brewed from 15 g of tea), 3) half-strength tea (brewed from 7.5 g tea) and 4) water containing 270 mg caffeine, equivalent to the concentration in the full-strength tea treatment. Subjects refrained from consuming caffeine or flavonoids for 4 d prior to the study. Tea was brewed each morning; beverages were consumed at room temperature as five 300 mL servings. Subjects received each treatment for 3 d; on the third day, EE was measured by indirect calorimetry in a room calorimeter. For the 3 d, subjects consumed a typical American diet. Energy content of the diet was tailored to each subject's needs as determined from a preliminary measure of 24-h EE by calorimetry. Relative to the water treatment, EE was significantly increased 2.9 and 3.4% for the full-strength tea and caffeinated water treatments, respectively. This increase over water alone represented an additional expenditure of 281 and 331 kJ/d for subjects treated with full-strength tea and caffeinated water, respectively. In addition, fat oxidation was significantly higher (12%) when subjects consumed the full-strength tea rather than water.

Absorptiometry, Photon↗
PubMed2002

Regular ingestion of tea does not inhibit in vivo lipid peroxidation in humans.

Prospective studies suggest that tea may protect against cardiovascular disease. A potential mechanism for such an effect involves inhibition of lipid peroxidation by polyphenolic antioxidants derived from tea. Our objective was to determine whether regular ingestion of tea could inhibit in vivo lipid peroxidation. Two controlled intervention studies assessed the effects of regular ingestion of tea on lipid peroxidation determined by measurement of urinary F(2)-isoprostane excretion. Study 1: The effects of 1000 mL/d of green tea and black tea were compared with hot water containing caffeine in 13 subjects with elevated blood pressure using a randomized 3-period (7 d each) crossover design. Study 2: The effects of 1250 mL/d of black tea were compared with hot water in 22 subjects with mildly raised serum total cholesterol concentrations using a randomized 2-period (4 wk each) crossover design. F(2)-isoprostane excretion was not altered after regular ingestion of green tea (273 +/- 48 pmol/mmol creatinine) or black tea (274 +/- 39 pmol/mmol creatinine) in comparison with hot water (263 +/- 47 pmol/mmol creatinine; Study 1), or by regular ingestion of black tea (334 +/- 71 pmol/mmol creatinine) in comparison with hot water (355 +/- 75 pmol/mmol creatinine; Study 2). These results do not support the suggestion that polyphenolic antioxidants derived from tea inhibit in vivo lipid peroxidation.

Adult↗
PubMed2003

Black tea consumption reduces total and LDL cholesterol in mildly hypercholesterolemic adults.

Despite epidemiological evidence that tea consumption is associated with the reduced risk of coronary heart disease, experimental studies designed to show that tea affects oxidative stress or blood cholesterol concentration have been unsuccessful. We assessed the effects of black tea consumption on lipid and lipoprotein concentrations in mildly hypercholesterolemic adults. Tea and other beverages were included in a carefully controlled weight-maintaining diet. Five servings/d of tea were compared with a placebo beverage in a blinded randomized crossover study (7 men and 8 women, consuming a controlled diet for 3 wk/treatment). The caffeine-free placebo was prepared to match the tea in color and taste. In a third period, caffeine was added to the placebo in an amount equal to that in the tea. Five servings/d of tea reduced total cholesterol 6.5%, LDL cholesterol 11.1%, apolipoprotein B 5% and lipoprotein(a) 16.4% compared with the placebo with added caffeine. Compared with the placebo without added caffeine, total cholesterol was reduced 3.8% and LDL cholesterol was reduced 7.5% whereas apolipoprotein B, Lp(a), HDL cholesterol, apolipoprotein A-I and triglycerides were unchanged. Plasma oxidized LDL, F2-isoprostanes, urinary 8-hydroxy-2'-deoxyguanosine, ex vivo ferric ion reducing capacity and thiobarbituric acid reactive substances in LDL were not affected by tea consumption compared with either placebo. Thus, inclusion of tea in a diet moderately low in fat reduces total and LDL cholesterol by significant amounts and may, therefore, reduce the risk of coronary heart disease. Tea consumption did not affect antioxidant status in this study.

Antioxidants↗
PubMed2003

Soy phytochemicals and tea bioactive components synergistically inhibit androgen-sensitive human prostate tumors in mice.

Although high doses of single bioactive agents may have potent anticancer effects, the chemopreventive properties of the Asian diet may result from interactions among several components that potentiate the activities of any single constituent. In Asia, where intake of soy products and tea consumption are very high, aggressive prostate cancer is significantly less prevalent in Asian men. The objective of the present study was to identify possible synergistic effects between soy and tea components on prostate tumor progression in a mouse model of orthotopic androgen-sensitive human prostate cancer. Soy phytochemical concentrate (SPC), black tea and green tea were compared with respect to tumorigenicity rate, primary tumor growth, tumor proliferation index and microvessel density, serum androgen level and metastases to lymph nodes. SPC, black tea and green tea significantly reduced tumorigenicity. SPC and black tea also significantly reduced final tumor weights. Green tea did not reduce final tumor weight, although it tended to elevate (P = 0.14) the serum dihydrotestosterone (DHT) concentration. The combination of SPC and black tea synergistically inhibited prostate tumorigenicity, final tumor weight and metastases to lymph nodes in vivo. The combination of SPC and green tea synergistically inhibited final tumor weight and metastasis and significantly reduced serum concentrations of both testosterone and DHT in vivo. Inhibition of tumor progression was associated with reduced tumor cell proliferation and tumor angiogenesis. This study suggests that further research is warranted to study the role of soy and tea combination as effective nutritional regimens in prostate cancer prevention.

Androgens↗
PubMed1994

Reduced risk of esophageal cancer associated with green tea consumption.

BACKGROUND: Studies in laboratory animals have suggested inhibitory effects of green tea on the induction of some cancers, notably, esophageal cancer. However, only a few epidemiologic studies have evaluated green tea as a potential inhibitor of human esophageal cancer. PURPOSE: Our purpose was to evaluate the relationship between green tea consumption and the risk of esophageal cancer. METHODS: This esophageal cancer study was part of a larger multicenter, case-control study that included three other gastrointestinal sites (pancreas, colon, and rectum). Medical records of patients aged 30-74 years old who were diagnosed with esophageal cancer from October 1, 1990, through January 31, 1993, were identified from the Shanghai Cancer Registry, which covers 6.8 million people in the urban area of Shanghai, People's Republic of China. During the ascertainment period, records of 1016 eligible cases of esophageal cancer were identified. Control subject records were selected by frequency matching in accordance with the age-sex distribution of the four gastrointestinal cancers ascertained by the cancer registry during 1986-1987. Patient interviews were then conducted using a structured, standardized questionnaire to obtain information on demographic characteristics, residential history, height and weight, diet, smoking, alcohol and tea drinking, medical history, family history of cancer, occupation, physical activity, and reproductive history. RESULTS: Of the 902 patients interviewed, 734 (81.4%) had their disease pathologically confirmed. There were 1552 control subjects interviewed, including 240 alternates. All analyses of tea effects were conducted separately among men and women and all were adjusted for age. After further adjustment for other known confounders, a protective effect of green tea drinking on esophageal cancer was observed among women (odds ratio [OR] = 0.50; 95% confidence interval [CI] = 0.30-0.83), and this risk decreased (P for trend < or = .01) as tea consumption increased. Among men, the ORs were also below 1.00, although not statistically significant. ORs for green tea intake were estimated among those persons who neither smoked nor drank alcohol. In this subset, statistically significant decreases in risk among tea drinkers were observed for both men (OR = 0.43; 95% CI = 0.22-0.86; P for trend = .05) and women (OR = 0.40; 95% CI = 0.20-0.77; P for trend < .001). CONCLUSIONS: This population-based, case-control study of esophageal cancer in urban Shanghai suggests a protective effect of green tea consumption. Although these findings are consistent with studies in laboratory animals, indicating that green tea can inhibit esophageal carcinogenesis, further investigations are definitely needed.

Adult↗
PubMed2003

Antimutagenic activity of tea: role of polyphenols.

PURPOSE OF REVIEW: Tea is considered to be one of the most promising dietary chemopreventive agents and, consequently, it is being studied extensively worldwide. Despite the fact that tea has proved very efficient in affording protection against chemical-induced cancer in animal models of the disease, epidemiological studies do not always support the laboratory findings, so that the value of tea as a human anticarcinogen may be considered as 'not proven'. A major mechanism of the anticarcinogenic activity of tea in animals is impairment of the interaction of carcinogens with DNA leading to mutations. The antimutagenic activity of tea as well as the underlying mechanisms will be reviewed, and the role of polyphenols, the postulated bioactive components, and caffeine will be critically evaluated. RECENT FINDINGS: In rats, exposure to tea modulated the disposition of heterocyclic amines, a major group of food-borne carcinogens, stimulating the pathways that lead to deactivation, and this is concordant with the established ability of tea to modulate the carcinogen-metabolizing enzyme systems. These observations provide a rational mechanism for the anticarcinogenic activity of tea in animals. SUMMARY: The beneficial activities of tea have always been attributed to the polyphenols, as these are present in tea at substantial concentrations and are endowed with antioxidant activity. It is becoming increasingly evident, however, that the bioavailability of these compounds is poor as a result of limited absorption and presystemic metabolism by mammalian and microbial enzymes. We propose that the biological activity of tea may be mediated by caffeine and microbial metabolites of polyphenols.

Animals↗
PubMed1981

Interaction of chlorpromazine with tea and coffee.

1 The interaction between phenothiazine neuroleptics with tea and coffee was studied in vitro. 2 Filtered infusions of tea and coffee caused precipitation of all the neuroleptics studied. Tea always caused a heavier precipitate than coffee. 3 The constituent or constituents of tea and coffee responsible for precipitating the neuroleptics was not identified. Solutions of caffeine, caffeine citrate and sodium chloride did not form a precipitate with chlorpromazine but precipitates were formed by sodium salicylate, sodium benzoate and trisodium citrate. 4 The interaction between chlorpromazine (CPZ) and tea was studied quantitatively using radiolabelled drug and it was found that the precipitation of [3H]-CPZ with a given quantity of tea was 'saturable'. The proportion of CPZ precipitated by a 'standard cup of tea' was 80% at low doses of the drug (10-40 mg) whilst at high doses (800 mg), the proportion of the drug precipitated was approximately 20%. 5 The interaction was further studied in vivo by the oral administration of tea and CPZ to rats. The cataleptic effect of CPZ was significantly reduced by the simultaneous administration of tea and this was apparently not due to the caffeine present in tea. 6 The results suggest that a substantial proportion of orally administered neuroleptic may be precipitated as a highly insoluble compound if coffee, or more especially tea, is taken close to drug administration. This interaction might affect the absorption of phenothiazines given orally to patients.

Animals↗
PubMed2006

A gene expression signature that can predict green tea exposure and chemopreventive efficacy of lung cancer in mice.

Green tea has been shown to be a potent chemopreventive agent against lung tumorigenesis in animal models. Previously, we found that treatment of A/J mice with either green tea (0.6% in water) or a defined green tea catechin extract (polyphenon E; 2.0 g/kg in diet) inhibited lung tumor tumorigenesis. Here, we described expression profiling of lung tissues derived from these studies to determine the gene expression signature that can predict the exposure and efficacy of green tea in mice. We first profiled global gene expressions in normal lungs versus lung tumors to determine genes which might be associated with the tumorigenic process (TUM genes). Gene expression in control tumors and green tea-treated tumors (either green tea or polyphenon E) were compared to determine those TUM genes whose expression levels in green tea-treated tumors returned to levels seen in normal lungs. We established a 17-gene expression profile specific for exposure to effective doses of either green tea or polyphenon E. This gene expression signature was altered both in normal lungs and lung adenomas when mice were exposed to green tea or polyphenon E. These experiments identified patterns of gene expressions that both offer clues for green tea's potential mechanisms of action and provide a molecular signature specific for green tea exposure.

Algorithms↗
PubMed2004

Effect of a 4-month tea intervention on oxidative DNA damage among heavy smokers: role of glutathione S-transferase genotypes.

Glutathione S-transferase (GST), a member of the phase II group of xenobiotic metabolizing enzymes, has been intensively studied at the levels of phenotype and genotype. The GST mu 1 (GSTM1) and GST theta 1 (GSTT1) genes have a null-allele variant in which the entire gene is absent. The null genotype for both enzymes has been associated with many different types of tumors. The aim of this study was to determine the possible differences in increased oxidative stress susceptibility to smoking within the GSTM1 and GSTT1 genotypes and the impact of high tea drinking on this. We designed a Phase II randomized, controlled, three-arm tea intervention trial to study the effect of high consumption (4 cups/day) of decaffeinated green or black tea, or water on oxidative DNA damage, as measured by urinary 8-hydroxydeoxyguanosine (8-OHdG), among heavy smokers over a 4-month period and to evaluate the roles of GSTM1 and GSTT1 genotypes as effect modifiers. A total of 133 heavy smokers (100 females and 33 males) completed the intervention. GSTM1 and GSTT1 genotype statuses were determined with a PCR-based approach. Multiple linear regression models were used to estimate the main effects and interaction effect of green and black tea consumption on creatinine-adjusted urinary 8-OHdG, with or without adjustment for potential confounders. Finally, we studied whether the effect of treatment varied by GSTM1 and GSTT1 status of the individual. Although there were no differences in urinary 8-OHdG between the groups at baseline, the between-group 8-OHdG levels at month 4 were statistically significant for GSTM1-positive smokers (P = 0.05) and GSTT1-positive smokers (P = 0.02). GSTM1-positive and GSTT1-positive smokers consuming green tea showed a decrease in urinary 8-OHdG levels after 4 months. Assessment of urinary 8-OHdG after adjustment for baseline measurements and other potential confounders revealed significant effect for green tea consumption (P = 0.001). The change from baseline was significant in both GSTM1-positive (t = -2.99; P = 0.006) and GSTT1-positive (P = 0.004) green tea groups, but not in the GSTM1-negative (P = 0.07) or GSTT1-negative (P = 0.909) green tea groups. Decaffeinated black tea consumption had no effect on urinary 8-OHdG levels among heavy smokers. Our data show that consumption of 4 cups of tea/day is a feasible and safe approach and is associated with a significant decrease in urinary 8-OHdG among green tea consumers after 4 months of consumption. This finding also suggests that green tea intervention may be effective in the subgroup of smokers who are GSTM1 and/or GSTT1 positive.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2006

Effects of repeated green tea catechin administration on human cytochrome P450 activity.

PURPOSE: Preclinical studies suggested that green tea or green tea catechins can modulate the activities of drug-metabolizing enzymes. We conducted this clinical study to determine the effect of repeated green tea catechin administration on human cytochrome P450 (CYP) enzyme activities. METHODS: Forty-two healthy volunteers underwent a 4-week washout period by refraining from tea or tea-related products. At the end of the washout period, study participants received a cocktail of CYP metabolic probe drugs, including caffeine, dextromethorphan, losartan, and buspirone for assessing the activity of CYP1A2, CYP2D6, CYP2C9, and CYP3A4, respectively. Blood and urine samples before and 8 h after probe drug administration were collected to determine parent drug and metabolite concentrations for measurements of baseline CYP enzyme activities. Following the baseline evaluation, study participants underwent 4 weeks of green tea catechin intervention at a dose that contains 800 mg epigallocatechin gallate (EGCG) daily. The green tea catechin product was taken on an empty stomach to optimize the p.o. bioavailability of EGCG. The EGCG dose given in this study exceeded the amounts provided by average green tea consumption. Upon completion of the green tea catechin intervention, the postintervention CYP enzyme activities were evaluated as described above. RESULTS: There are large between-subject variations in CYP enzyme activities in healthy individuals. Four weeks of green tea catechin intervention did not alter the phenotypic indices of CYP1A2, CYP12D6, and CYP12C9, but resulted in a 20% increase (P = 0.01) in the area under the plasma buspirone concentration-time profile, suggesting a small reduction in CYP3A4 activity. CONCLUSIONS: We conclude that repeated green tea catechin administration is not likely to result in clinically significant effects on the disposition of drugs metabolized by CYP enzymes.

Administration, Oral↗
PubMed2001

Short- and long-term black tea consumption reverses endothelial dysfunction in patients with coronary artery disease.

BACKGROUND: Epidemiological studies suggest that tea consumption decreases cardiovascular risk, but the mechanisms of benefit remain undefined. Endothelial dysfunction has been associated with coronary artery disease and increased oxidative stress. Some antioxidants have been shown to reverse endothelial dysfunction, and tea contains antioxidant flavonoids. Methods and Results-- To test the hypothesis that tea consumption will reverse endothelial dysfunction, we randomized 66 patients with proven coronary artery disease to consume black tea and water in a crossover design. Short-term effects were examined 2 hours after consumption of 450 mL tea or water. Long-term effects were examined after consumption of 900 mL tea or water daily for 4 weeks. Vasomotor function of the brachial artery was examined at baseline and after each intervention with vascular ultrasound. Fifty patients completed the protocol and had technically suitable ultrasound measurements. Both short- and long-term tea consumption improved endothelium- dependent flow-mediated dilation of the brachial artery, whereas consumption of water had no effect (P<0.001 by repeated-measures ANOVA). Tea consumption had no effect on endothelium-independent nitroglycerin-induced dilation. An equivalent oral dose of caffeine (200 mg) had no short-term effect on flow-mediated dilation. Plasma flavonoids increased after short- and long-term tea consumption. CONCLUSIONS: Short- and long-term black tea consumption reverses endothelial vasomotor dysfunction in patients with coronary artery disease. This finding may partly explain the association between tea intake and decreased cardiovascular disease events.

Administration, Oral↗