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Esta es una lista de estudios científicos publicados en ingles sobre el té en la salud:

(1): Green and black teas inhibit atherosclerosis by lipid, antioxidant, and fibrinolytic mechanisms.

Vinson JA; Teufel K; Wu N

Department of Chemistry, University of Scranton, Scranton, Pennsylvania18510-4626

Tea is the most widely consumed beverage in the world, second only to water. Most laypersons and scientists believe that green tea is healthier than black tea due to the low incidence of heart disease and cancer in the Orient. Here, we report the first dose-response comparison of a green and black tea on normal hamsters after long-term supplementation and on a hamster model of atherosclerosis. Both teas were equally effective in inhibiting atherosclerosis with the lower dose decreasing it 26-46% and the high dose decreasing it 48-63%. Atherosclerosis was inhibited by three mechanisms: hypolipemic, antioxidant, and antifibrinolytic. There was a significant correlation between atherosclerosis and the three mechanisms. In the normal animals, teas also caused some improvement in plasma low density lipoprotein (LDL), LDL/high density lipoprotein ratio, triglycerides, lipid peroxides, lower density lipoprotein lipid peroxides, and fibrinogen. Isolated lower density lipoprotein oxidizability was also reduced in all groups. Green and black teas were equally effective at human equivalent doses, thus confirming human intervention and epidemiology studies and providing mechanisms for teas' benefit.

(2): Black tea increases coronary flow reserve in healthy males.

.Hirata K; Shimada K; Watanabe H; Otsuka R; Tokai K; Yoshiyama M; Homma S; Yoshikawa J

Columbia University, College of Physicians & Surgeons, Department of Medicine, Division of Cardiology, New York, New York, USA.

Epidemiologic studies suggest that tea consumption decreases the risk for cardiovascular events. However, there has been no clinical report examining the effects of tea consumption on coronary circulation. The purpose of this study was to evaluate the effects of black tea on coronary flow velocity reserve (CFVR) using transthoracic Doppler echocardiography (TTDE). This was a double-blind crossover study of 10 healthy male volunteers conducted to compare the effects of black tea and caffeine on coronary circulation. The coronary flow velocity of the left anterior descending coronary artery was measured at baseline and at hyperemia during adenosine triphosphate infusion by TTDE to determine CFVR. The CFVR ratio was defined as the ratio of CFVR after beverage consumption to CFVR before beverage consumption. All data were divided into 2 groups according to beverage type: group T (black tea) and group C (caffeine). Two-way analysis of variance showed a significant group effect and interaction in CFVR before and after beverage consumption ( [Formula: see text] ). CFVR significantly increased after tea consumption in group T (4.5 +/- 0.9 vs 5.2 +/- 0.9, p <0.0001). The CFVR ratio of group T was larger than that of group C (1.18 +/- 0.07 vs 1.04 +/- 0.08, [Formula: see text] ). Acute black tea consumption improves coronary vessel function, as determined by CFVR.

(3): Comparison of antioxidant activity and bioavailability of tea epicatechins with their epimers. Author(s): Zhen-Yu Chen ; Jin Ze Xu ; Sai Ying Venus Yeung ; Qi Chang ; Yu Huang ; Zhen-Yu Chen 

Source: British Journal of Nutrition,  Volume: 91 Number: 6 Page: 873 - 881

DOI: 10.1079/BJN20041132     Publisher: CABI Publishing 

Abstract: Canned and bottled tea drinks contain not only green tea epicatechins (GTE), namely (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epicatechin (EC), but also four GTE epimers, namely (-)-gallocatechin gallate (GCG), (-)-catechin gallate (CG), (-)-gallocatechin (GC) and (-)-catechin (C). In the present study we examined the antioxidant activity and bioavailability of these epimers compared with their corresponding precursors. The epimerisation reaction was induced by autoclaving GTE extract derived from longjing green tea at 120°C for 20 min. Isolation and purification of each GTE and epimer were accomplished by various column chromatographic and semi-preparative HPLC techniques. The antioxidant activity of each epimer with its corresponding GTE precursor was conducted in the three in vitrosystems, namely human LDL oxidation, ferric reducing-antioxidant power (FRAP), and anti-2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical assays. The results of all three assays demonstrated that CG had similar antioxidant activity with its precursor ECG, while GC was less potent as an antioxidant than its precursor EGC. Regarding EGCG and GCG, the antioxidant potency was similar for both LDL oxidation and DPPH free radical assays, but GCG was statistically less effective than EGCG in the FRAP assay. For EC and C, the latter had less anti-free radical activity in the DPPH assay, but in LDL oxidation and FRAP assays the antioxidant activity was similar. Oral and intravenous dosing of GTE-epimer mixture led to increase in total plasma antioxidant capacity in rats. In general, both epicatechins and epimers had low bioavailability (0·08-0·31) and most of the observed differences between epicatechins and their corresponding epimers were small, even if they were statistically significant in some cases. It was concluded that the epimerisation reaction occurring in manufacturing canned and bottled tea drinks would not significantly affect antioxidant activity and bioavailability of total tea polyphenols.

(4): Protective effect of green tea against prostate cancer: a case control study in southeast China.

Jian L; Xie LP; Lee AH; Binns CW

School of Public Health, Curtin University of Technology, 

Perth, WA, Australia

To investigate whether green tea consumption has an etiological association with prostate cancer, a case-control study was conducted in Hangzhou, southeast China during 2001-2002. The cases were 130 incident patients with histologically confirmed adenocarcinoma of the prostate. The controls were 274 hospital inpatients without prostate cancer or any other malignant diseases, and matched to the age of cases. Information on duration, quantity and frequency of usual tea consumption, as well as the number of new batches brewed per day, were collected by face-to-face interview using a structured questionnaire. The risk of prostate cancer for tea consumption was assessed using multivariate logistic regression adjusting for age, locality, education, income, body mass index, physical activity, alcohol consumption, tobacco smoking, total fat intake, marital status, age at marriage, number of children, history of vasectomy and family history of prostate cancer. Among the cases, 55.4% were tea drinkers compared to 79.9% for the controls. Almost all the tea consumed was green tea. The prostate cancer risk declined with increasing frequency, duration and quantity of green tea consumption. The adjusted odds ratio (OR), relative to non-tea drinkers, were 0.28 (95% CI = 0.17-0.47) for tea drinking, 0.12 (95% CI = 0.06-0.26) for drinking tea over 40 years, 0.09 (95% CI = 0.04-0.21) for those consuming more than 1.5 kg of tea leaves yearly, and 0.27 (95% CI = 0.15-0.48) for those drinking more than 3 cups (1 litre) daily. The dose response relationships were also significant, suggesting that green tea is protective against prostate cancer.

 (5): Green tea and gastrointestinal cancer risk.

Borrelli F; Capasso R; Russo A; Ernst E

Department of Experimental Pharmacology, University of Naples 'Federico II', Naples,Italy.

BACKGROUND: : Gastrointestinal cancer is one of the leading causes of cancer mortality in the world. Therefore, numerous efforts are being made to find chemoprotective substances able to reduce its incidence. Amongst these, green tea, one of the most popular beverages world-wide, has been reported to provide protective effects against gastrointestinal cancer. AIM: To critically evaluate all epidemiological studies reporting an association between green tea consumption and a reduced risk of gastrointestinal cancer. METHODS: : Epidemiological studies of green tea consumption in relation to gastrointestinal cancer or preneoplastic lesions were identified through computerized literature searches using the following databases: Medline (Pubmed), Embase, Amed, CISCOM, Phytobase and Cochrane Library. Only epidemiological studies indicating the type of tea (green tea) and the site of either cancer or precancerous lesions (stomach or intestine) were included. No language restrictions were imposed.

RESULTS: : Twenty-one epidemiological investigations met our inclusion/exclusion criteria.

CONCLUSION: : These studies seemed to suggest a protective effect of green tea on adenomatous polyps and chronic atrophic gastritis formations. By contrast, there was no clear epidemiological evidence to support the suggestion that green tea plays a role in the prevention of stomach and intestinal cancer.

(6): Mel and Enid Zuckerman Arizona College of Public Health, University of Arizona, Tucson, AZ,  85724, USA.

Tea drinking has been associated with decreased occurrence of cancer and heart disease. One potential mechanism for these findings is the strong antioxidant effect of tea polyphenols. A phase II randomized controlled tea intervention trial was designed to study the effect of high consumption (4 cups/d) of decaffeinated green or black tea on oxidative DNA damage as measured by urinary 8-hydroxydeoxyguanosine (8-OHdG) among smokers over a 4-mo period. A total of 143 heavy smokers, aged 18-79 y, were randomized to drink either green or black tea or water. Levels of plasma and urinary catechins and urinary 8-OHdG were measured monthly. A total of 133 of 143 smokers completed the 4-mo intervention. 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. Plasma and urinary levels of catechins rose significantly in the green tea group compared with the other two groups. Assessment of urinary 8-OHdG after adjustment for baseline measurements and other potential confounders revealed a highly significant decrease in urinary 8-OHdG (-31%) after 4 mo of drinking decaffeinated green tea (P = 0.002). No change in urinary 8-OHdG was seen among smokers assigned to the black tea group. These data suggest that regular green tea drinking might protect smokers from oxidative damages and could reduce cancer risk or other diseases caused by free radicals associated with smoking. J Nutr. 2003 Oct;133(10):3303S-3309S

(7): Tea consumption and cardiovascular disease: effects on endothelial function.

Vita JA

Evans Department of Medicine and Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA, USA

Epidemiological studies suggest that tea consumption is associated with reduced cardiovascular disease risk, but the mechanisms for these observations have remained uncertain. In recent years, it has become apparent that the endothelium plays a central role in the regulation of vascular homeostasis and that endothelial dysfunction contributes to the pathogenesis and clinical expression of cardiovascular disease. This article reviews the evidence that human tea consumption has a beneficial effect on the vascular endothelium and the clinical implications of these findings.
J Nutr. 2003 Oct;133(10):3293S-3297S

(8): Antihyperglycemic Effect of Oolong Tea in Type 2 Diabetes.

Hosoda K, Wang MF, Liao ML, Chuang CK, Iha M, Clevidence B, Yamamoto S.

OBJECTIVE-To determine the efficacy of oolong tea for lowering plasma glucose in type 2 diabetic patients in Miaoli, Taiwan. 

RESEARCH DESIGN AND METHODS-A total of 20 free-living subjects who had type 2 diabetes and took hyperglycemic drugs as prescribed were enrolled in the present study. Subjects consumed oolong tea (1,500 ml) or water for 30 days each in a randomized crossover design. Tea was not consumed for 14 days prior to treatments. RESULTS:-Relative to initial concentrations, oolong tea markedly lowered concentrations of plasma glucose (from 229 +/- 53.9 to 162.2 +/- 29.7 mg/dl, P < 0.001) and fructosamine (from 409.9 +/- 96.1 to 323.3 +/- 56.4 micro mol/l, P < 0.01), whereas the water control group had not changed (208.7 +/- 61.0 vs. 232.3 +/- 63.1 mg/dl for glucose and from 368.4 +/- 85.0 to 340.0 +/- 76.1 micro mol/l for fructosamine).

CONCLUSIONS: Oolong tea may be an effective adjunct to oral hypoglycemic agents in the treatment of type 2 diabetes.

 
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