فوائد الشاى الأسود
Protective effect of black and green tea against carbon tetrachloride-induced oxidative stress in rats.
Department of Community Health Sciences, College of Applied Medical Sciences, King Saud University, PO Box 10219,11433, .
OBJECTIVE: To assess the effects of green and black tea on carbon tetrachloride (CCl4)-induced oxidative stress in rats. METHODS: This study was completed in the period of January to April 2005. Male wistar albino rats (6 weeks old) were randomly assigned to one of 3 diets (12 rats/group), control diet, black tea diet, or green tea diet. At the end of dietary treatment, a single dose of CCl4 (2.5 ml/kg intraperitoneally) in paraffin (1:1 v/v) was given to 6 rats in each group after overnight fasting. The remaining 6 rats of each group received the same amount of paraffin only intraperitoneally. Thiobarbituric acid reactive substance were used as indicators of oxidative stress. The results were further confirmed by tissue histopathology. RESULTS: The present study demonstrates that there was a significant (p<0.001) increase in alanine aminotransferase (ALT) activity, TBARS, and in vitro hemolysis; and a significant (p<0.05) decrease in total plasma antioxidant status by CCl4 injection. However, green and black tea supplemented groups treated with CCl4 showed protective effects, as the in vitro hemolysis, ALT, TBARS levels were significantly lowered and total plasma antioxidant activity was significantly raised compared to the control group injected with CCl4. The endogenous antioxidant component glutathione (GSH) was significantly (p<0.001) raised in groups fed with green/black tea prior to CCl4 injection as compared to controls treated with CCl4. CONCLUSION: The results of this study suggest that both black and green tea possess preventive effects against CCl4 induced damage in rats.
1: Int J Food Sci Nutr. 2000 Sep;51(5):309-15.
Consumption of black tea elicits an increase in plasma antioxidant potential in humans.
Division of Health and Life Sciences, University College.
Epidemiological studies suggest that the consumption of tea flavonoids may be associated with reduced risk of coronary heart disease, stroke and cancer-related deaths. The flavonoids are polyphenols which in vitro exhibit antioxidant properties. Tea flavonoids are known to be rapidly absorbed into the circulation following oral ingestion. To date few studies have demonstrated that these bioavailable flavonoids retain antioxidant properties in vivo. Nine healthy subjects aged between 26 and 59 (one male and eight females) took part in 3 study days. On 1 day subjects consumed no tea and on the other 2 days subjects drank either black tea with milk, or black tea alone at hourly intervals between 9.00 a.m. and 14.00 p.m. Blood was sampled at 9.00 a.m. and at 12.00 p.m. and 15.00 p.m. The antioxidant potential of plasma was determined using the ferric reducing antioxidant power (FRAP) assay. Subjects consuming no tea exhibited no significant change in FRAP across the 6 hours of the study day. Similarly consumption of milky tea produced no change in FRAP between 9.00 a.m. and 12.00 p.m. and the 50% increase in FRAP noted between 12.00 p.m. and 15.00 p.m. was not statistically significant. When the subjects consumed black tea without milk FRAP increased by 65% between 9.00 a.m. and 12.00 p.m. (P = 0.02) and at 15.00 p.m. was 76% higher than at 9.00 a.m. (P = 0.002). Heavy consumption of black tea thus appears to elevate circulating antioxidant potentials in vivo. This is an effect which appears to be totally negated by the drinking of tea with milk. Although tea may thus represent an important source of dietary antioxidants in many societies, the role of tea in reducing risk of major disease states needs to be investigated in more detail.
PMID: 11103296 [PubMed - indexed for MEDLINE]
1: Nutr Cancer. 2005;52(1):15-21.
Associations between black tea and coffee consumption and risk of lung cancer among current and former smokers.
Department of Epidemiology, Roswell Park Cancer Institute,.
Although cigarette smoking is a clear risk factor for lung cancer, the other determinants of lung cancer risk among smokers are less clear. Tea and coffee contain catechins and flavonoids, which have been shown to exhibit anticarcinogenic properties. Conversely, caffeine may elevate cancer risk through a variety of mechanisms. The current study investigated the effects of regular consumption of black tea and coffee on lung cancer risk among 993 current and former smokers with primary incident lung cancer and 986 age-, sex-, and smoking-matched hospital controls with non-neoplastic conditions. Results indicated that lung cancer risk was not different for those with the highest black tea consumption (>or=2 cups/day) compared with nondrinkers of tea [adjusted odds ratio (aOR)=0.90; 95% confidence interval (CI)=0.66-1.24]. However, elevated lung cancer risk was observed for participants who consumed 2-3 cups of regular coffee daily (aOR=1.34; 95% CI=0.99-1.82) or >or=4 cups of regular coffee daily (aOR=1.51, 95% CI=1.11-2.05). In contrast, decaffeinated coffee drinking was associated with decreased lung cancer risk for both participants who consumed <or=1 cup/day (aOR=0.67; 95% CI=0.54-0.84) and those who consumed >or=2 cups/day (aOR=0.64; 95% CI=0.51-0.80). These results suggest that any chemoprotective effects of phytochemicals in coffee and tea may be overshadowed by the elevated risk associated with caffeine in these beverages.
PMID: 16090999 [PubMed - indexed for MEDLINE]
1: Int J Food Sci Nutr. 2005 Dec;56(8):551-9.
Comparison of the antioxidant activity of roasted tea with green, oolong, and black teas.
Research Center for Animal Hygiene and Food Safety,University of Agriculture and Veterinary Medicine, 080-8555, .
Although the antioxidant properties of green, oolong, and black teas have been well studied, antioxidant activity has not been examined in roasted tea. Therefore, in the current studies, we investigated the antioxidant activity of roasted tea in comparison with those of green, oolong, and black teas. Using water extracts of the various teas, we examined the total phenolic content as well as the antioxidant activities, including the reducing power, the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, and the inhibition of hemolysis caused by 2,2'-azo-bis(2-amidinopropane) dihydrochloride (AAPH)-induced lipid oxidation in erythrocyte membranes. The roasted tea contained lower levels of total phenolics than green, oolong, or black tea (green tea > oolong tea > black tea > roasted tea). The relative reducing power and DPPH scavenging activity decreased in the following order: green tea > roasted tea > oolong tea > black tea. Also, green tea was more effective against AAPH-induced erythrocyte hemolysis than other teas (green tea>roasted tea = oolong tea = black tea). These results suggest that roasted tea is beneficial to health, in humans, because of its high antioxidant activity.
PMID: 16638659 [PubMed - indexed for MEDLINE]
Br J Nutr. 2006 May;95(5):989-95.
High tea consumption diminishes salivary 17beta-estradiol concentration in Polish women.
Department of General Biochemistry, Faculty of Biotechnology, Jagiellonian University, Gronostajowa 7,.
We hypothesized that among reproductive-age women consuming large quantities of tea, the production of estradiol would be suppressed. It has been shown that catechins and theaflavines, the major constituents of tea, inhibit aromatase, an enzyme which catalyses the conversion of androgens to oestrogens. Our study included Polish women living in urban (n 61) and rural (n 48) areas. Women collected daily saliva samples for one complete menstrual cycle and filled out dietary questionnaires. Saliva samples were analysed by RIA for concentration of 17beta-estradiol (E2). Women with high (above the median) average daily consumption of black tea had reduced levels of salivary E2 in comparison with women who drank less black tea (below the median). This effect was observed within the whole study group, as well as separately within urban (P=0.0006) and rural (P=0.013) groups. High intake of the sum of subclasses of tea catechins and epigallocatechin gallate, assessed using the http://www.nal.usda.gov), was also associated with lower concentrations of E2 within all women (P=0.01 and P=0.0001, respectively) and within the urban group (P=0.0001 and P=0.004, respectively). Similar relationships were observed between the sum of subclasses of theaflavines and thearubigines and E2 levels for the whole group (P=0.002) and for urban women (P=0.02). Women with high consumption of tea had lower levels of E2 concentration throughout the entire menstrual cycle. These results may have implications for reducing hormone-related cancer risk by a relatively easy dietary intervention.Department of Agriculture database (
PMID: 16611391 [PubMed - indexed for MEDLINE]
1: Int J Food Sci Nutr. 2005 Dec;56(8):543-50.
Ethyl acetate extract from black tea prevents neuromuscular blockade by botulinum neurotoxin type A in vitro.
Research Center for Animal Hygiene and Food Safety,University of Agriculture and Veterinary Medicine, , 080-8555, .
Botulinum neurotoxin produced by Clostridium botulinum is the strongest neurotoxin and causes botulism in mammals. The current study aimed to find an inactivator for botulinum neurotoxin in black, oolong, roasted, and green teas. The ability of the four teas to inactivate the neuromuscular blocking action of botulinum neurotoxin was determined. Water extracts from black, oolong, and roasted teas protected against the toxicity of botulinum neurotoxin type A in mouse phrenic nerve-diaphragm preparations. The order of potency of the water extracts was black tea > oolong tea > roasted tea > green tea (no effect). The effects of several organic solvent extracts of black tea water extract were examined, and the order of potency was ethyl acetate extract > butanol extract = remaining extract > chloroform extract (no effect). Ethyl acetate extracts from oolong, roasted, and green tea water extracts also exhibited a stronger protecting effect than chloroform, butanol, and remaining extracts from these teas, but they had weaker protective effect than ethyl acetate extract from black tea water extract. These protective effects occurred only when each extract was pre-mixed with the toxin before the assay, and they were not modified by mixing each extract with bovine serum albumin (BSA) before adding the toxin. These results indicate that ethyl acetate extract from black tea is the best source for searching for tea-derived inactivating substance(s) of botulinum neurotoxin.
PMID: 16638658 [PubMed - indexed for MEDLINE]
The mechanism underlying the protective effect of the thearubigin fraction of black tea (Camellia sinensis) extract against the neuromuscular blocking action of botulinum neurotoxins.
Department of Pharmacology, University ofSchool of Veterinary Medicine , 080-8555, .
The aim of the present study was to elucidate the mechanism of the protective effect of black tea extract, the thearubigin fraction, against the neuromuscular blocking action of botulinum neurotoxin types A, B, and E. The effects of thearubigin fraction extracted from a black tea infusion were examined on the neuromuscular blocking action of botulinum neurotoxin types A, B, and E in mouse phrenic nerve-diaphragm preparations and on the binding of these toxins to rat cerebrocortical synaptosomes. Botulinum neurotoxin type A (1.5 nM), B (6 nM), or E (5 nM) abolished indirect twitches in mouse phrenic nerve-diaphragm preparations within 50, 90, 90 min., respectively. Thearubigin fraction mixed with each toxin blocked the inhibitory effect of the toxins. The specific binding of [125I]botulinum neurotoxin type A, B, or E to rat cerebrocortical synaptosomes was inhibited by mixing iodinated toxin with thearubigin fraction. The elution profile of [125I]botulinum neurotoxin type A, B, or E on Sephadex G-50 column chromatography was different from that of toxin mixed with thearubigin fraction. These findings indicate that thearubigin fraction protects against the neuromuscular blocking action of botulinum neurotoxin types A, B, and E by binding with the toxins.
PMID: 12076314 [PubMed - indexed for MEDLINE]
1: Carcinogenesis. 2006 Jul;27(7):1301-9. Epub 2006 Apr 25.
Green tea, black tea and colorectal cancer risk: a meta-analysis of epidemiologic studies.
The Cancer Center , University of, .
Experimental studies have supported tea as a chemopreventive agent for colorectal cancer. No quantitative summary of the epidemiologic evidence on tea and colorectal cancer risk has ever been performed. The current meta-analysis included 25 papers conducted in 11 countries across three continents (North America,and ). Summary odds ratios (ORs) for highest versus non/lowest tea consumption levels were calculated based on fixed and random effects models. The meta-regression and stratified methods were used to examine heterogeneity across studies. For green tea, the combined results from eight studies indicated a reduced risk of colorectal cancer with intake [summary OR = 0.82, 95% confidence interval (CI) = 0.69-0.98]. The protective effect is mainly found among the three case-control studies of colon cancer (summary OR = 0.74, 95% CI = 0.60-0.93). Results from studies of rectal cancer irrespective of study design (case-control versus cohort) (summary OR = 0.99, 95% CI = 0.71-1.37) and cohort studies of colon cancer (summary OR = 0.99, 95% CI = 0.79-1.24) were compatible with the null hypothesis. For black tea, the summary OR derived from 20 studies was 0.99 (95% CI = 0.87-1.13). There is wide divergence in results across the 20 individual studies; formal tests for homogeneity across studies revealed statistically significant differences in findings across all studies (P < 0.001), amongst the 7 cohort studies (P = 0.002), and amongst the 13 case-control studies (P < 0.001). Despite the strong evidence from in vitro and non-human in vivo studies in support of green and black tea as potential chemopreventive agents against colorectal cancer, available epidemiologic data are insufficient to conclude that either tea type may protect against colorectal cancer in humans.
PMID: 16638787 [PubMed - indexed for MEDLINE]
1: J Stud Alcohol. 2006 Jul;67(4):510-8.
Protective effect of black tea against ethanol-induced oxidative modifications of liver proteins and lipids.
Department of Analytical Chemistry, Medical University of Bialystok,8, P.O. Box 14, .
OBJECTIVE: Black tea has been recently ascertained as a source of water-soluble antioxidants that may enhance cellular antioxidant abilities. The present study was designed to investigate the efficacy of the preventive effect of black tea on oxidative modifications of liver lipids and proteins of 2-month-old rats intoxicated chronically (28 days) with ethanol. METHOD: Lipid peroxidation was estimated by measurement of lipid hydroperoxides, malondialdehyde, and 4-hydroxynonenal by high-performance liquid chromatography (HPLC) and by spectrophotometric determination of conjugated dienes. The markers of protein oxidative modification products-bistyrosine and tryptophan-were quantified by spectrofluorimetry, whereas levels of amino, sulfhydryl, and carbonyl groups were estimated spectrophotometrically. RESULTS: Ethanol intoxication caused changes in liver antioxidant abilities that led to the generation of oxidative stress and, consequently, to the significant increase in products of lipid and protein oxidative modification. Enhanced lipid peroxidation was confirmed by assessment of the concentration of lipid peroxidation products measured at all examined levels. Protein modifications were evidenced by increase in levels of bistyrosine and carbonyl groups and by decrease in concentration of tryptophan and levels of sulfhydryl and amino groups. The metabolic consequences of oxidative modifications of lipids and proteins were reduced by cathepsin B activity and translocation of this lysosomal protease into cytosol as well as markers of liver damage-alanine aminotransferase (ALT) and aspartate aminotransferase (AST)-into the blood serum. Administration of black tea to ethanol-intoxicated rats partially protected antioxidant parameters and, remarkably, prevented the significant increase in concentrations of all measured lipid peroxidation products. Moreover, the levels of markers of the protein-modification process were similar to those of the control group. Protection of biological membranes by black tea prevents changes in the permeability of these membranes and translocation of the examined enzymes. CONCLUSIONS: Our findings indicate that black tea protects proteins and lipids against oxidative modification induced by chronic ethanol intoxication, which preserves changes in redox and proteolytic homeostasis.
PMID: 16736070 [PubMed - in process]
1: J Am Coll Nutr. 2006 Jun;25(3):216-23.
Acute effect of black and green tea on aortic stiffness and wave reflections.
Ist Department of Cardiology,Medical School , Hippokration Hospital , .
OBJECTIVE: While most studies have shown an inverse relation between tea consumption and cardiovascular risk, other studies have shown opposite results. Aortic stiffness and wave reflections are markers of cardiovascular disease and prognosticators of cardiovascular risk. METHODS: The acute effect of black and green tea on aortic stiffness and wave reflections was assessed in 29 healthy volunteers in a randomized, single-blind, sham-procedure controlled, cross-over design. In the black tea sub-study, 16 subjects received 6 gm of tea, caffeine (175 mg), or hot water in 3 different sessions. In the green tea sub-study, 13 subjects received 6 gm of tea, caffeine (125 mg), or hot water. Carotid-femoral pulse wave velocity and wave reflection indices were measured at baseline and for 3 hours after consumption. RESULTS: Black tea increased pulse wave velocity during the first 90 min (increase by 0.49 m/sec, P < 0.05), showing a rapid return towards baseline values thereafter (P = 0.07 for the whole study period); in contrast, green tea had no effect. Both black and green tea increased augmentation index (by 5.0% and by 6.6%, P < 0.01 and P < 0.001, respectively) throughout the study. These changes were less than the respective changes produced by caffeine. Both black and green tea had a significant pressor effect. No change in oxidant status was found with both types of tea. CONCLUSIONS: Both black and green tea increases acutely wave reflections and only black tea increases aortic stiffness. Tea flavonoids may play a role in the attenuation of the effects of caffeine contained in tea.
PMID: 16766780 [PubMed - indexed for MEDLINE]
Tea polyphenols and theaflavins are present in prostate tissue of humans and mice after green and black tea consumption.
Department of Pathology, VA.
Green and black tea have shown promise in the chemoprevention of prostate cancer. The objective of this study was to determine the bioavailability and bioactivity of tea polyphenols (PP) and theaflavins in human serum and human and mouse tissues. A decaffeinated black tea diet was administered to C57BL/6 mice. PPs and theaflavins were found in the small and large intestine, liver, and prostate in conjugated and free forms. The relative prostate bioavailability of theaflavin was 70% higher than that of epigallocatechin gallate (EGCG). In the second mouse study, a green tea (GT) diet was administered followed by the control diet for 1-5 d. Epicatechin (EC), EGCG, and epicatechin gallate (ECG) concentrations in prostate tissue were significantly decreased after 1 d of consuming the control diet. Epigallocatechin gallate (EGC), however, did not decrease significantly. For the human study, 20 men scheduled for surgical prostatectomy were randomly assigned to consume 1.42 L daily of GT, BT, or a caffeine-matched soda control (SC) for 5 d before radical prostatectomy. Tea PPs were greater in prostate samples from men consuming BT and GT than in men consuming SC (P = 0.0025). Although tea PP were not detectable in serum, ex vivo LNCaP prostate cancer cell proliferation was less when cells were grown in media containing patient serum collected after BT (P < 0.001) and GT (P = 0.025) consumption relative to baseline serum This is the first human study to show that tea polyphenols and theaflavins are bioavailable in the prostate where they may be active in the prevention of prostate cancer.