Effects of Green Tea Extract on Insulin Resistance and Glucagon-Like Peptide 1 in Patients with Type 2 Diabetes and Lipid Abnormalities: A Randomized, Double-Blinded, and Placebo-Controlled Trial The effect of an extract of green and black tea on glucose control in adults with type 2 diabetes mellitus: double-blind randomized study. Does green tea affect postprandial glucose, insulin and satiety in healthy subjects: a randomized controlled trial Randomized controlled trial for an effect of green tea consumption on insulin resistance and inflammation markers. Cancer prevention by green tea: evidence from epidemiologic studies. Bioavailability and antioxidant activity of tea flavanols after consumption of green tea, black tea, or a green tea extract supplement. The impact of the catechol-O-methyltransferase genotype on the acute responsiveness of vascular reactivity to a green tea extract. The Minnesota Green Tea Trial (MGTT), a randomized controlled trial of the efficacy of green tea extract on biomarkers of breast cancer risk: study rationale, design, methods, and participant characteristics The impact of the catechol-O-methyltransferase genotype on vascular function and blood pressure after acute green tea ingestion. Diet supplementation with green tea extract epigallocatechin gallate prevents progression to glucose intolerance in db/db mice Prospective Cohort Study of Green Tea Consumption and Colorectal Cancer Risk in Women The Effect of Ginkgo biloba and Camellia sinensis Extracts on Psychological State and Glycemic Control in Patients with Type 2 Diabetes Mellitus Effects of Green Tea Supplementation on Elements, Total Antioxidants, Lipids, and Glucose Values in the Serum of Obese Patients Coffee, tea, and incident type 2 diabetes: the Singapore Chinese Health Study.
The aim of this study is to investigate the effect of green tea extract on patients with type 2 diabetes mellitus and lipid abnormalities on glycemic and lipid profiles , and hormone peptides by a double-blinded , r and omized and placebo-controlled clinical trial . This trial enrolled 92 subjects with type 2 diabetes mellitus and lipid abnormalities r and omized into 2 arms , each arm comprising 46 participants . Of the participants , 39 in therapeutic arm took 500 mg green tea extract , three times a day , while 38 in control arm took cellulose with the same dose and frequency to complete the 16-week study . Anthropometrics measurements , glycemic and lipid profiles , safety parameters , and obesity-related hormone peptides were analyzed at screening and after 16-week course . Within-group comparisons showed that green tea extract caused a significant decrease in triglyceride and homeostasis model assessment of insulin resistance index after 16 weeks . Green tea extract also increased significantly high density lipoprotein cholesterol . The HOMA-IR index decreased from 5.4±3.9 to 3.5±2.0 in therapeutic arm only . Adiponectin , apolipoprotein A1 , and apolipoprotein B100 increased significantly in both arms , but only glucagon-like peptide 1 increased in the therapeutic arm . However , only decreasing trend in triglyceride was found in between-group comparison . Our study suggested that green tea extract significantly improved insulin resistance and increased glucagon-like peptide 1 only in within-group comparison . The potential effects of green tea extract on insulin resistance and glucagon-like peptide 1 warrant further investigation . Trial Registration Clinical Trials.gov Recent evidence suggests that tea from Camellia sinensis ( eg , green , oolong , and black tea ) may have a hypoglycemic effect . We evaluated the ability of an extract of green and black tea to improve glucose control over a 3-month period . A double-blind , placebo-controlled , r and omized multiple-dose ( 0 , 375 , or 750 mg per day for 3 months ) study in adults with type 2 diabetes mellitus not taking insulin was performed . The primary end point was change in glycosylated hemoglobin at 3 months . The 49 subjects who completed this study were predominantly white with an average age of 65 years and a median duration of diabetes of 6 years , and 80 % of them reported using hypoglycemic medication .  After 3 months , the mean changes in glycosylated hemoglobin were + 0.4 ( 95 % confidence interval , 0.2 - 0.6 ) , + 0.3 ( 0.1 - 0.5 ) , and + 0.5 ( 0.1 - 0.9 ) in the placebo , 375-mg , and 750-mg arms , respectively . The changes were not significantly different between study arms . We did not find a hypoglycemic effect of extract of green and black tea in adults with type 2 diabetes mellitus Background Results of epidemiological studies have suggested that consumption of green tea could lower the risk of type 2 diabetes .  Intervention studies show that green tea may decrease blood glucose levels , and also increase satiety . This study was conducted to examine the postpr and ial effects of green tea on glucose levels , glycemic index , insulin levels and satiety in healthy individuals after the consumption of a meal including green tea . Methods The study was conducted on 14 healthy volunteers , with a crossover design . Participants were r and omized to either 300 ml of green tea or water . This was consumed together with a breakfast consisting of white bread and sliced turkey . Blood sample s were drawn at 0 , 15 , 30 , 45 , 60 , 90 , and 120 minutes . Participants completed several different satiety score scales at the same times . Results Plasma glucose levels were higher 120 min after ingestion of the meal with green tea than after the ingestion of the meal with water . No significant differences were found in serum insulin levels , or the area under the curve for glucose or insulin . Subjects reported significantly higher satiety , having a less strong desire to eat their favorite food and finding it less pleasant to eat another mouthful of the same food after drinking green tea compared to water . Conclusions Green tea showed no glucose or insulin-lowering effect . However , increased satiety and fullness were reported by the participants after the consumption of green tea . Trial registration To study the effects of the intake of green tea and polyphenols , which are a component of green tea , on insulin resistance and systemic inflammation , a r and omized controlled trial was conducted on 66 patients aged 32 - 73 y ( 53 males and 13 females ) with borderline diabetes or diabetes . Subjects in the intervention group were asked to take a packet of green tea extracts/powder containing 544 mg polyphenols ( 456 mg catechins ) daily , which was a dose that could be taken without difficulty , and were asked to divide the green tea extracts/powder in a packet into 3 or 4 fractions dissolved in hot water everyday and to take a fraction after every meal or snack for 2 mo , in addition to daily food intake . The subjects in the control group were simply followed . To calculate the level of green tea polyphenol intake that the subject usually drank at home , the subject was asked to taste 3 teas of different strengths ( 1 , 2 and 3 % ) and the tea that was closest to the one that the subject drank at home , was selected by each subject . After 2 mo , the mean daily polyphenol intake in the intervention group was 747 mg , which was significantly higher than that of 469 mg in the control group . In the intervention group , the body weight , BMI , systolic and diastolic blood pressures , blood glucose level , Hb A1c level , insulin level and HOMA index after taking the supplementation for 2 mo , were lower than the respective value before intervention : however , these parameters in the intervention group at 2 mo did not significantly differ from those in the control group . Within the intervention group , changes in insulin level tended to be associated with changes in polyphenol intake . In addition , changes in BMI were associated with changes in blood glucose level and insulin level . In conclusion , the daily supplementary intake of 500 mg green tea polyphenols did not have clear effects on blood glucose level , Hb A1c level , insulin resistance or inflammation markers . The positive correlation between the level of polyphenol intake and insulin level warrants further studies on the effect of green tea on insulin resistance In contrast to the consistent results of an inhibitory effect of green tea extracts and tea polyphenols on the development and growth of carcinogen-induced tumors in experimental animal models , results from human studies are mixed . Both observational and intervention studies have provided evidence in support of a protective role of green tea intake in the development of oral-digestive tract cancer or an inhibitory role of oral supplementation of green tea extract on a precancerous lesion of oral cavity . Evidence in support of green tea intake against the development of liver cancer risk is limited and inconsistent . An inverse association between  green tea intake and lung cancer risk has been observed among never smokers but not among smokers . Although observational studies do not support a beneficial role of tea intake against the development of prostate cancer , several phase 2 clinical trials have shown an inhibitory effect of green tea extract against the progression of prostate premalignant lesions to malignant tumors . Prospect i ve epidemiologic studies so far have not provided evidence for a protective effect of green tea consumption on breast cancer development . Current data neither confirm nor refute a definitive cancer-preventive role of green tea intake . Large r and omized intervention trials on the efficacy of green tea polyphenols or extracts are required before a recommendation for green tea consumption for cancer prevention should be made BACKGROUND Green and black tea polyphenols have been extensively studied as cancer chemopreventive agents . Many in vitro experiments have supported their strong antioxidant activity . Additional in vivo studies are needed to examine the pharmacokinetic relation of absorption and antioxidant activity of tea polyphenols administered in the form of green or black tea or tea extract supplements . OBJECTIVE The purpose of this study was to compare the pharmacokinetic disposition of tea polyphenols and their effect on the antioxidant capacity in plasma 8 h after a bolus consumption of either green tea , black tea , or a green tea extract supplement . DESIGN Thirty healthy subjects were r and omly assigned to 3 different sequences of green tea , black tea , or a green tea extract supplement in a 3 x 3 crossover design with a 1-wk washout period in between treatments . RESULTS Flavanol absorption was enhanced when tea polyphenols were administered as a green tea supplement in capsule form and led to a small but significant increase in plasma antioxidant activity compared with when tea polyphenols were consumed as black tea or green tea . All 3 interventions provided similar amounts of (-)-epigallocatechin-3-gallate . CONCLUSIONS Our observations suggest that green tea extract supplements retain the beneficial effects of green and black tea and may be used in future chemoprevention studies to provide a large dose of tea polyphenols without the side effects of caffeine associated with green and black tea beverages The beneficial effects of green tea catechins , such as the proposed improvement in endothelial function , may be influenced by phase II metabolism during and after absorption . The methylation enzyme , catechol-O-methyltransferase ( COMT ) , has a missense mutation rs4680 ( G to A ) , proposed to result in a 40 % reduction in enzyme activity . In the present pilot study , twenty subjects ( ten of each homozygous COMT genotype ) were recruited .  Green tea extract capsules ( 836 mg green tea catechins ) were given in a fasted state , and a high-carbohydrate breakfast was given after 60 min . Blood sample s and vascular function measurements were taken at regular intervals . The change in digital volume pulse stiffness index ( SI ) from baseline was shown to be different between genotype groups at 120 and 240 min , with a lower SI in the GG individuals ( P ≤ 0·044 ) . The change in blood pressure from baseline also differed between genotype groups , with a greater increase in systolic ( P = 0·023 ) and diastolic ( P = 0·034 ) blood pressure at 120 min in the GG group . The GG [ corrected ] group was shown to have a greater increase in insulin concentrations at 120 min ( P = 0·019 ) and 180 min ( P = 0·008 ) compared with baseline , despite similar glucose profiles . No genotypic differences were found in vascular reactivity measured using laser Doppler iontophoresis , total nitrite , lipids , plasma total antioxidant capacity or inflammatory markers after ingestion of the green tea extract . In conclusion , SI and insulin response to the glucose load differed between the COMT genotype groups , and this may be suggestive of a green tea extract and genotype interaction Purpose The Minnesota Green Tea Trial ( MGTT ) was a r and omized , placebo-controlled , double-blinded trial investigating the effect of daily green tea extract consumption for 12 months on biomarkers of breast cancer risk . Methods Participants were healthy postmenopausal women at high risk of breast cancer due to dense breast tissue with differing catechol-O-methyltransferase ( COMT ) genotypes . The intervention was a green tea catechin extract containing 843.0 ± 44.0 mg/day epigallocatechin gallate or placebo capsules for 1 year . Annual digital screening mammograms were obtained at baseline and month 12 , and fasting blood and 24-h urine sample s were provided at baseline and at months 6 and 12 . Primary endpoints included changes in percent mammographic density , circulating endogenous sex hormones , and insulin-like growth factor axis proteins ; secondary endpoints were changes in urinary estrogens and estrogen metabolites and circulating F2-isoprostanes , a biomarker of oxidative stress . Results The MGTT screened more than 100,000 mammograms and r and omized 1,075 participants based on treatment  ( green tea extract vs. placebo ) , stratified by COMT genotype activity ( high COMT vs. low/intermediate COMT genotype activity ) . A total of 937 women successfully completed the study and 138 dropped out ( overall dropout rate = 12.8 % ) . Conclusions In this paper we report the rationale , design , recruitment , participant characteristics , and methods for biomarker and statistical analyses SCOPE Evidence for the benefits of green tea catechins on vascular function is inconsistent , with genotype potentially contributing to the heterogeneity in response . Here , the impact of the catechol-O-methyltransferase ( COMT ) genotype on vascular function and blood pressure ( BP ) after green tea extract ingestion are reported . METHODS AND RESULTS Fifty subjects ( n = 25 of the proposed low-activity [ AA ] and of the high-activity [ GG ] COMT rs4680 genotype ) , completed a r and omized , double-blind , crossover study . Peripheral arterial tonometry , digital volume pulse ( DVP ) , and BP were assessed at baseline and 90 min after 1.06 g of green tea extract or placebo . A 5.5 h and subsequent 18.5 h urine collection was performed to assess green tea catechin excretion . A genotype × treatment interaction was observed for DVP reflection index ( p = 0.014 ) , with green tea extract in the AA COMT group attenuating the increase observed with placebo . A tendency for a greater increase in diastolic BP was evident at 90 min after the green tea extract compared to placebo ( p = 0.07 ) . A genotypic effect was observed for urinary methylated epigallocatechin during the first 5.5 h , with the GG COMT group demonstrating a greater concentration ( p = 0.049 ) . CONCLUSION Differences in small vessel tone according to COMT genotype were evident after acute green tea extract Background Green tea was suggested as a therapeutic agent for the treatment of diabetes more than 70 years ago , but the mechanisms behind its antidiabetic effect remains elusive . In this work , we address this issue by feeding a green tea extract ( TEAVIGO ™ ) with a high content of epigallocatechin gallate ( EGCG ) or the thiazolidinedione PPAR-γ agonist rosiglitazone , as positive control , to db/db mice , an animal model for diabetes . Methods Young ( 7 week-old ) db/db mice were r and omized and assigned to receive diets supplemented with or without EGCG or rosiglitazone for 10 weeks . Fasting blood glucose , body weight and food intake was measured along the treatment . Glucose and insulin levels were determined during an oral glucose tolerance test after 10 weeks of treatment . Pancreata were sample d at the end of the study for blinded histomorphometric analysis . Islets were isolated and their mRNA expression analyzed by quantitative RT-PCR . Results The results show that , in db/db mice , EGCG  improves glucose tolerance and increases glucose-stimulated insulin secretion . EGCG supplementation reduces the number of pathologically changed islets of Langerhans , increases the number and the size of islets , and heightens pancreatic endocrine area . These effects occurred in parallel with a reduction in islet endoplasmic reticulum stress markers , possibly linked to the antioxidative capacity of EGCG . Conclusions This study shows that the green tea extract EGCG markedly preserves islet structure and enhances glucose tolerance in genetically diabetic mice . Dietary supplementation with EGCG could potentially contribute to nutritional strategies for the prevention and treatment of type 2 diabetes Tea and its constituents have shown anticarcinogenic activities in in vitro and animal studies . Epidemiologic studies , however , have been inconsistent . We prospect ively evaluated the association between green tea consumption and  colorectal cancer ( CRC ) risk in a cohort of 69,710 Chinese women aged 40 to 70 years . Information on tea consumption was assessed through in-person interviews at baseline and reassessed 2 to 3 years later in a follow-up survey . During 6 years of follow-up , 256 incident cases of CRC were identified . The multivariate relative risk of CRC was 0.63 ( 95 % confidence interval , 0.45 - 0.88 ) for women who reported drinking green tea regularly at baseline compared with nonregular tea drinkers . A significant dose-response relationship was found for both the amount of tea consumed ( P trend = 0.01 ) and duration in years of lifetime tea consumption ( P trend = 0.006 ) . The reduction in risk was most evident among those who consistently reported to drink tea regularly at both the baseline and follow-up surveys ( relative risk , 0.43 ; 95 % confidence interval , 0.24 - 0.77 ) . The inverse association with regular tea drinking was observed for both colon and rectal cancers . This study suggests that regular consumption of green tea may reduce CRC risk in women . ( Cancer Epidemiol Biomarkers Prev 2007;16(6):1219–23 Interest in finding natural antioxidants for use in food or medical material s to prevent free radical imbalance has increased considerably over the past years . The aim of this research was to evaluate changes in glycemic control and psychological state of patients with type 2 diabetes mellitus ( T2DM ) after use of antioxidant plant preparations .  Fifty-six patients with T2DM were r and omly allocated to receive st and ardized Ginkgo biloba L. leaves dry extract , green tea dry extract , or placebo capsules .  Diabetes glycemic control measured as glycated hemoglobin ( HbA1c ) level , antioxidant state and psychological data were evaluated at baseline , after 9 and 18 months of using either antioxidant preparations or placebo . The level of perceived stress lowered significantly after 9 months ( p=0.038 ) and 18 months ( p=0.030 ) , and the psychological aspect of quality of life significantly improved after 18 months ( p=0.019 ) of use of G. biloba extract . No significant differences were detected after using green tea extract . In patients using placebo , significant lowering of HbA1c level was observed after 18 months ( p=0.017 ) . In conclusion , antioxidant G. biloba leaf extract exhibited a mild effect on psychological state and a trend of improving glycemic control in patients with type 2 diabetes mellitus The consumption of green tea has been associated with cardiovascular and metabolic diseases . There have been some studies on the influence of green tea on the mineral status of obese subjects , but they have not yielded conclusive results . The aim of the present study is to examine the effects of green tea extract on the mineral , body mass , lipid profile , glucose , and antioxidant status of obese patients . A r and omized , double-blind , placebo-controlled study was conducted . Forty-six obese patients were r and omly assigned to receive either 379 mg of green tea extract , or a placebo , daily for 3 months . At baseline , and after 3 months of treatment , the anthropometric parameters , blood pressure , and total antioxidant status were assessed , as were the levels of plasma lipids , glucose , calcium , magnesium , iron , zinc , and copper . We found that 3 months of green tea extract supplementation result ed in decreases in body mass index , waist circumference , and levels of total cholesterol , low-density cholesterol , and triglyceride . Increases in total antioxidant level and in zinc concentration in serum were also observed . Glucose and iron levels were lower in the green tea extract group than in the control , although HDL-cholesterol and magnesium were higher in the green tea extract group than in the placebo group . At baseline , a positive correlation was found between calcium and body mass index , as was a negative correlation between copper and triglycerides . After 3 months , a positive correlation between iron and body mass index and between magnesium and HDL-cholesterol , as well as a negative correlation between magnesium and glucose , were observed . The present findings demonstrate that green tea influences the body 's mineral status . Moreover , the results of this study confirm the beneficial effects of green tea extract supplementation on body mass index , lipid profile , and total antioxidant status in patients with obesity BACKGROUND Increasing coffee intake was inversely associated with risk of type 2 diabetes in population s of European descent ; however , data from high-risk Asian population s are lacking as are data on tea intake in general . OBJECTIVE We investigated the prospect i ve associations between intakes of coffee , black tea , and green tea with the risk of type 2 diabetes in Singaporean Chinese men and women . DESIGN We analyzed data from 36 908 female and male participants in the Singapore Chinese Health Study aged 45 - 74 y in 1993 - 1998 who had multiple diet and lifestyle measures assessed and then were followed up between 1999 and 2004 . We used Cox regression models to investigate the association of baseline coffee and tea intakes with incident type 2 diabetes during follow-up , with adjustment for a number of possible confounding or mediating variables . RESULTS In multivariate models participants reporting > or = 4 cups of coffee/d had a 30 % reduction in risk of diabetes [ relative risk ( RR ) : 0.70 ; 95 % CI : 0.53 , 0.93 ] compared with participants who reported nondaily consumption . Participants reporting > or = 1 cup of black tea/d had a suggestive 14 % reduction in risk of diabetes ( RR : 0.86 ; 95 % CI : 0.74 , 1.00 ) compared with participants who reported 0 cups/d , and we observed no association with green tea . CONCLUSION Regular consumption of coffee and potentially black tea , but not green tea , is associated with lower risk of type 2 diabetes in Asian men and women in Singapore
The consumption of green tea did not decrease the levels of fasting plasma glucose , fasting serum insulin , OGTT-2 h glucose , haemoglobin A₁c and HOMA(IR ) in population s at risk of T2DM .
BACKGROUND Although the regular consumption of green tea or green tea extract has been considered to improve insulin sensitivity , the reported results are inconsistent .
Therefore , we conducted a meta- analysis to evaluate the effect of green tea or green tea extract on insulin sensitivity and glycaemic control in population s at risk of type 2 diabetes mellitus ( T2DM ) .