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. Green tea and the prevention of breast cancer: a case-control study in Southeast China. Consumption of green or black tea does not increase resistance of low-density lipoprotein to oxidation in humans. Double-blinded, placebo-controlled trial of green tea extracts in the clinical and histologic appearance of photoaging skin. Tea catechin consumption reduces circulating oxidized low-density lipoprotein. The Relationship between Green Tea and Total Caffeine Intake and Risk for Self-Reported Type 2 Diabetes among Japanese Adults A Population-Based Case-Control Study of Lung Cancer and Green Tea Consumption among Women Living in Shanghai, China Effect of 2-Month Controlled Green Tea Intervention on Lipoprotein Cholesterol, Glucose, and Hormone Levels in Healthy Postmenopausal Women Cholesterol-lowering effect of a theaflavin-enriched green tea extract: a randomized controlled trial. Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans.
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 Breast cancer is the most common malignancy in women worldwide .  Tea has anticarcinogenic effects against breast cancer in experimental studies . However , epidemiologic evidence that tea protects against breast cancer has been inconsistent . A case-control study was conducted in Southeast China between 2004 and 2005 . The incidence cases were 1009 female patients aged 20 - 87 years with histologically confirmed breast cancer . The 1009 age-matched controls were healthy women r and omly recruited from breast disease clinics . Information on duration , frequency , quantity , preparation , type of tea consumption , diet and lifestyle were collected by face-to-face interview using a vali date d and reliable question naire . Conditional logistic regression analyses were used to estimate odds ratios ( ORs ) and associated 95 % confidence intervals . Compared with non-tea drinkers , green tea drinkers tended to reside in urban , have better education and have higher consumption of coffee , alcohol , soy , vegetables and fruits . After adjusting established and potential confounders , green tea consumption was associated with a reduced risk of breast cancer . The ORs were 0.87 ( 0.73 - 1.04 ) in women consuming 1 - 249 g of dried green tea leaves per annum , 0.68 ( 0.54 - 0.86 ) for 250 - 499 g per annum , 0.59 ( 0.45 - 0.77 ) for 500 - 749 g per annum and 0.61 ( 0.48 - 0.78 ) for > or=750 g per annum , with a statistically significant test for trend ( P < 0.001 ) . Similar dose-response relationships were observed for duration of drinking green tea , number of cups consumed and new batches prepared per day . We conclude that regular consumption of green tea can protect against breast cancer . More research to closely examine the relationship between tea consumption and breast cancer risk is warranted Epidemiologic studies indicated that tea consumption reduces the risk of cardiovascular disease . We assessed the effect of green or black tea consumption on resistance of low-density lipoprotein ( LDL ) to oxidation ex vivo and on serum lipid concentrations in healthy volunteers . In a 4-wk parallel comparison trial , 45 volunteers consumed 900 mL ( 6 cups ) mineral water , green tea , or black tea/d . Blood sample s drawn while subjects were fasting were obtained before and after the study . The effect on resistance of subsequently isolated LDL to oxidation of adding green or black tea extract to plasma was investigated in an in vitro experiment . Consumption of 900 mL ( 6 cups ) green or black tea/d did not affect serum lipid concentrations , resistance of LDL to oxidation , or markers of oxidative damage to lipids in vivo , although consumption of green tea slightly increased total antioxidant activity of plasma . The in vitro experiment showed that resistance of isolated LDL to oxidation increased only after incubation of plasma with very high amounts of green or black tea . These amounts , when converted to tea catechin concentrations , were much higher than those expected in vivo . We conclude that daily consumption of 900 mL ( 6 cups ) green or black tea/d for 4 wk had no effect on serum lipid concentrations or resistance of LDL to oxidation ex vivo . Future research should focus on mechanisms by which tea flavonoids may reduce the risk of cardiovascular disease other than by increasing the intrinsic antioxidant status of LDL BACKGROUND Green tea extracts have gained popularity as ingredients in topical skin care preparations to treat aging skin . Green tea polyphenolic compounds have significant antioxidant and anti-inflammatory activities , and studies suggest that these extracts help mediate ultraviolet radiation damage . OBJECTIVE To evaluate the effects of a combination regimen of topical and oral green tea supplementation on the clinical and histologic characteristics of photoaging . METHODS Forty women with moderate photoaging were r and omized to either a combination regimen of 10 % green tea cream and 300 mg twice-daily green tea oral supplementation or a placebo regimen for 8 weeks . RESULTS No significant differences in clinical grading were found between the green tea-treated and placebo groups , other than higher subjective scores of irritation in the green tea-treated group . Histologic grading of skin biopsies did show significant improvement in the elastic tissue content of treated specimens ( p<.05 ) . CONCLUSION Participants treated with a combination regimen of topical and oral green tea showed histologic improvement in elastic tissue content . Green tea polyphenols have been postulated to protect human skin from the cutaneous signs of photoaging , but clinical ly significant changes could not be detected . Longer supplementation may be required for clinical ly observable improvements It has been reported that green tea consumption reduces the risk of coronary artery disease and cardiac events . Catechin is a major constituent of Japanese green tea and an antioxidant . Lipids and oxidization of low-density lipoprotein cholesterol ( LDL-C ) play important roles in atherosclerosis . Therefore , we evaluated the effect of catechin intake on the lipid profile and plasma oxidized LDL . The study population consisted of 40 healthy adult volunteers ( 10 men , 30 women ) . Catechin was extracted from green tea leaves . The subjects were r and omly divided into two groups , a catechin group ( n = 29 ) and a control group ( n = 11 ) . In the catechin group , catechin ( 500 mg : equivalent to 6 or 7 cups of green tea ) was administered orally . Venous blood sample s were obtained before eating a meal at the start and after 4 weeks without any lifestyle modification . Plasma oxidized LDL assay was performed with a s and wich-type enzyme immunoassay using anti-oxidized phosphatidylcholine monoclonal antibody . The baseline lipid profiles and tea consumptions were similar between the two groups . Plasma oxidized LDL was significantly decreased after catechin administration ( from 9.56 + /- 9.2 to 7.76 + /- 7.7 U/mL , P = 0.005 ) , while plasma LDL-C , triglyceride , and HDL-C concentrations did not change . Catechin decreased the plasma oxidized LDL concentration without significant change in plasma LDL concentration . The mechanism of the beneficial effects of green tea on coronary artery disease might result from a decrease in plasma oxidized LDL Context Caffeine intake from coffee has been associated with a lower incidence of diabetes . Research ers have not studied the relationship of green tea , a popular beverage in Japan , where the incidence of diabetes is increasing rapidly . Contributions The authors estimated the intake of caffeine-containing beverages in a community-based survey in Japan and measured the 5-year incidence of diabetes . Greater intake of green tea or coffee was associated with a reduced incidence of diabetes . The effect of green tea was largely observed in women , was dose-related , and reflected caffeine intake . Implication s Higher intake of caffeine , whether from coffee or green tea , is associated with a lower incidence of diabetes . The Editors The prevalence of type 2 diabetes has increased worldwide , particularly in Asian countries where it was previously low ( 1 ) . In Japan , population -based studies have shown a 2-fold increase in the prevalence of diabetes during the past 2 decades , from 5 % to 10 % to 10 % to 15 % ( 2 ) . Several cohort studies done in Europe and in the United States reported an association between coffee consumption , a major source of caffeine , and reduced risk for diabetes ( 3 - 7 ) . Although these studies did not show any association between consumption of black tea and the risk for diabetes , they did not examine the effect of green or oolong teas , major sources of caffeine in Asian countries . Consumption of green tea is common in Japan ; 80 % of the population drinks green tea , and the average consumption per capita is 2 cups per day ( 8) . We wanted to determine whether there is a relationship between consumption of green tea and the risk for type 2 diabetes and , if so , whether caffeine fully accounts for this relationship . To examine these questions , we analyzed data from a large cohort study of 19487 middle-aged men and women in 25 communities across Japan . We also examined the effect of age , sex , body mass index ( BMI ) , family history , smoking status , alcohol use , magnesium intake , and physical activity on the association between this mode of caffeine consumption and risk for diabetes . Methods The Japan Collaborative Cohort Study for Evaluation of Cancer Risk ( JACC Study ) started between 1988 and 1990 . A total of 110792 individuals ( 46465 men and 64327 women ) who were 40 to 79 years of age and living in 45 communities across Japan participated in municipal health screening examinations and completed self-administered question naires regarding lifestyle and medical history of cardiovascular disease and cancer ( 9 ) . Informed consent was obtained before the completion of the question naire . Participants from 25 of the 45 communities completed 5-year follow-up surveys . Among 35690 participants ( 15177 men and 20513 women ) who were 40 to 65 years of age at baseline without a history of type 2 diabetes , stroke , coronary heart disease , or cancer , 17413 individuals ( 49 % ; 6727 men and 10686 women ) completed the 5-year follow-up question naire and provided valid responses on tea or coffee consumption and history of type 2 diabetes . The data from these 17413 individuals were used for the analyses . The mean age of the nonrespondents was 1 year younger for men ( 52.3 vs. 53.3 years of age ) and did not differ for women ( 53.1 vs. 53.0 years of age ) compared with the respondents . The mean BMI and the prevalence of a BMI of 25.0 kg/m2 or greater did not differ between the respondents and nonrespondents . Mean BMI was 22.7 kg/m2 versus 22.8 kg/m2 for men and 22.8 kg/m2 versus 22.9 kg/m2 for women , respectively ; the prevalence of overweight was 18 % versus 19 % for men and 21 % versus 22 % for women , respectively . The ethical committees at Nagoya University and the University of Tsukuba approved the study . Assessment of Consumption of Tea and Coffee and Caffeine Intake At baseline , consumption of tea and coffee  was assessed by using a self-administered dietary question naire . Participants were asked to state their average consumption of green tea , black tea , oolong tea , and coffee during the previous year . They could select any of 4 frequency responses : less than once a week , about 1 to 2 times a week , about 3 to 4 times a week , and almost every day . Participants who selected the response of almost every day were also asked to state their average consumption of these beverages in number of cups per day . We classified the categories of consumption as less than 1 cup per week , 1 to 6 cups per week , 1 to 2 cups per day , 3 to 5 cups per day , and 6 or more cups per day . The highest 2 or 3 consumption categories were combined for coffee , black tea , and oolong tea because of the small number of participants in these categories . The consumption of decaffeinated coffee or tea  was not recorded because these products were not commercially available in Japan in the early 1990s . The total intake of caffeine was calculated by adding the caffeine content from each specific beverage ( 1 cup for coffee or tea ) and multiplying it by the participant 's weight proportional to the frequency of caffeine use . We estimated the size of the cup for each beverage from a validation study ( 10 ) and the caffeine content per 100 mL of each beverage from the Japan Food Tables ( 11 ) . The estimated caffeine content was 153 mg per cup ( 170 mL ) of coffee , 30 mg per cup ( 200 mL ) of green tea , 51 mg per cup ( 170 mL ) of black tea , and 38 mg per cup ( 190 mL ) of oolong tea . The mean caffeine intake was 229 mg/d for men and 215 mg/d for women .  Relative proportions of caffeine intake by beverage were 46 % from green tea , 44 % to 47 % from coffee , 3 % from black tea , and 4 % to 5 % from oolong tea . For reproducibility , the Spearman correlation coefficients between the 2 question naires , administered 1 year apart for 85 participants ( 8 men and 77 women ) , were 0.79 for green tea , 0.87 for coffee , 0.77 for black tea , and 0.56 for oolong tea ( 10 ) . The validity of the data was confirmed for the 85 participants by comparing the data from the question naire with those from four 3-day dietary records collected approximately 3 to 4 months apart ( 10 ) . The mean frequency of consumption of green tea  was 25.4 cups per week according to the question naire and 30.1 cups per week according to four 1-week dietary records ( Spearman correlation coefficient , 0.47 ) . The respective mean frequencies were 8.0 cups and 7.1 cups per week with a correlation coefficient of 0.79 for coffee , 1.4 cups and 1.6 cups per week with a correlation coefficient of 0.70 for black tea , and 1.8 cups and 1.2 cups per week with a correlation coefficient of 0.55 for oolong tea . When we restricted the data to the 77 women , the results were essentially the same . Assessment of Diabetes Cases Participants who reported having diabetes newly diagnosed by physicians on the 5-year follow-up question naire were considered to have incident diabetes . To examine the validity of self-reporting of diabetes , we compared self-report data with laboratory findings and treatment status in a sample of 1230 men and 1837 women . We considered elevated glucose concentrations ( fasting serum glucose concentration 7.8 mmol/L [ 140 mg/dL ] or a r and omly measured concentration of 11.1 mmol/L [ 200 mg/dL ] ) or treatment with oral hypoglycemic agents or insulin to indicate new cases of diabetes . Recent criteria from the American Diabetes Association ( 12 ) were not used because the cases in our study were diagnosed before 1995 . The sensitivity of self-reporting was 70 % for men and 75 % for women ; the specificity was 95 % for men and 98 % for women . Statistical Analysis To examine potential confounding variables reported from previous studies ( 3 - 7 ) , we presented baseline characteristics according to the frequency of consumption for each beverage . Tests for trends were conducted by using the median values of confounding variables in each category of beverage ; the linear regression model was used for continuous variables , and the logistic regression model was used for categorical variables . The odds ratios for incident type 2 diabetes were calculated in each category of beverage consumption and in each quartile of caffeine intake ; less than 1 cup per week or the lowest quartile was used as the reference category . We estimated age , sex , and BMI -adjusted odds ratios and multivariable odds ratios using the logistic regression model , adjusting for age ( in years ) , sex , sex-specific quintiles of BMI ( weight in kilograms divided by the square of height in meters ) , parental history of diabetes ( yes or no ) , smoking status ( never , former , or current [ 1 to 19 , 20 to 29 , or 30 cigarettes/d ] ) , alcohol intake ( never , former , or current [ 1 to 22 , 23 to 45 , 46 to 68 , or 69 g/d ] ) , sex-specific quintiles of magnesium intake , hours of walking ( < 0.5 , 0.5 , 0.6 to 0.9 , and 1.0 h/d ) , and hours of participation in sports ( < 1 , 1 to 2 , 3 to 4 , and 5 h/wk ) . Sex-specific quintiles of BMI and magnesium intake were used because of different distributions between the sexes . We adjusted for magnesium intake because previous cohort studies indicated an inverse association between magnesium intake and risk for diabetes ( 13 , 14 ) . We conducted a test for trend by treating median values of each category of beverage or caffeine intake as continuous variables . We examined the association between caffeine intake and the risk for diabetes stratified by age group ( 40 to 54 years and 55 to 65 years ) , sex , family history of diabetes ( yes or no ) , current smoking status ( yes or no ) ,  current alcohol intake ( yes or no ) ,  magnesium  intake ( below and above the sex-specific median ) , BMI ( < 25.0 kg/m2 and 25.0 kg/m2 ) , hours of walking ( < 0.5 and 0.5 h/d ) , and hours of participation in sports ( < 5 and 5 h/wk ) . The interactions with these stratified variables were tested by using cross-product terms of caffeine intake and the stratified variables . All analyses were conducted by using the SAS statistical package , version 8.2 ( SAS Institute Inc. , Cary , North Carolina ) . P values for statistical tests were 2-tailed , and 95 % CIs were estimated . Role of Epidemiologic evidence regarding the association between the consumption of green tea and lung cancer is limited and inconclusive , although experimental studies have shown consistently that tea preparations and tea polyphenols may inhibit the induction of a variety of cancers , including lung cancer . In this population -based case-control study , we examined the association between past consumption of green tea and the risk of lung cancer . We identified 649 incident cases of primary lung cancer among women diagnosed from February 1992 through January 1994 using the population -based Shanghai Cancer Registry . We r and omly selected a control group of 675 women from the Shanghai Residential Registry , frequency-matched to the expected age distribution of the cases .  Green tea consumption was ascertained through face-to-face interviews . We estimated adjusted odds ratios ( ORs ) and 95 % confidence intervals ( 95 % CIs ) using unconditional logistic regression . Among nonsmoking women , consumption of green tea was associated with a reduced risk of lung cancer ( OR = 0.65 ; 95 % CI = 0.45–0.93 ) , and the risks decreased with increasing consumption . We found little association , however , among women who smoked ( OR = 0.94 ; 95 % CI = 0.40–2.22 ) . The inconsistency in the association between drinking tea and the risk of lung cancer reported in previous studies may in part be due to inadequate control of confounding of active smoking There have been no controlled intervention studies to investigate the effects of green tea on circulating hormone levels , an established breast cancer risk factor . We conducted a double-blind , r and omized , placebo-controlled intervention study to investigate the effect of the main green tea catechin , epigallocatechin gallate ( EGCG ) , taken in a green tea extract , polyphenon E ( PPE ) . Postmenopausal women ( n = 103 ) were r and omized into three arms : placebo , 400-mg EGCG as PPE , or 800-mg EGCG as PPE as capsules per day for 2 months . Urinary tea catechin and serum estrogen , and rogen , lipid , glucose-related markers , adiponectin , and growth factor levels were measured at baseline and at the end of months 1 and 2 of intervention . On the basis of urinary tea catechin concentrations , compliance was excellent . Supplementation with PPE did not produce consistent patterns of changes in estradiol ( E2 ) , estrone ( E1 ) , or testosterone ( T ) levels . Low-density lipoprotein (LDL)-cholesterol decreased significantly in both PPE groups but was unchanged in the placebo group ; the change in LDL-cholesterol differed between the placebo and PPE groups ( P = 0.02 ) . Glucose and insulin levels decreased nonsignificantly in the PPE groups but increased in the placebo group ; statistically significant differences in changes in glucose ( P = 0.008 ) and insulin ( P = 0.01 ) were found . In summary , green tea ( 400- and 800-mg EGCG as PPE ; ∼5–10 cups ) supplementation for 2 months had suggestive beneficial effects on LDL-cholesterol concentrations and glucose-related markers . Cancer Prev Res ; 5(3 ) ; 393–402 . © 2012 AACR BACKGROUND Tea consumption has been associated with decreased cardiovascular risk , but potential mechanisms of benefit are ill-defined . While epidemiologic studies suggest that drinking multiple cups of tea per day lowers low-density lipoprotein cholesterol ( LDL-C ) , previous trials of tea drinking and administration of green tea extract have failed to show any impact on lipids and lipoproteins in humans . Our objective was to study the impact of a theaflavin-enriched green tea extract on the lipids and lipoproteins of subjects with mild to moderate hypercholesterolemia . METHODS Double-blind , r and omized , placebo-controlled , parallel-group trial set in outpatient clinics in 6 urban hospitals in China . A total of 240 men and women 18 years or older on a low-fat diet with mild to moderate hypercholesterolemia were r and omly assigned to receive a daily capsule containing theaflavin-enriched green tea extract ( 375 mg ) or placebo for 12 weeks . Main outcome measures were mean percentage changes in total cholesterol , LDL-C , high-density lipoprotein cholesterol ( HDL-C ) , and triglyceride levels compared with baseline . RESULTS After 12 weeks , the mean + /- SEM changes from baseline in total cholesterol , LDL-C , HDL-C , and triglyceride levels were -11.3 % + /- 0.9 % ( P = .01 ) , -16.4 % + /- 1.1 % ( P = .01 ) , 2.3 % + /- 2.1 % ( P = .27 ) , and 2.6 % + /- 3.5 % ( P = .47 ) , respectively , in the tea extract group . The mean levels of total cholesterol , LDL-C , HDL-C , and triglycerides did not change significantly in the placebo group . No significant adverse events were observed . CONCLUSION The theaflavin-enriched green tea extract we studied is an effective adjunct to a low-saturated-fat diet to reduce LDL-C in hypercholesterolemic adults and is well tolerated BACKGROUND Current interest in the role of functional foods in weight control has focused on plant ingredients capable of interfering with the sympathoadrenal system . OBJECTIVE We investigated whether a green tea extract , by virtue of its high content of caffeine and catechin polyphenols , could increase 24-h energy expenditure ( EE ) and fat oxidation in humans . DESIGN Twenty-four-hour EE , the respiratory quotient ( RQ ) , and the urinary excretion of nitrogen and catecholamines were measured in a respiratory chamber in 10 healthy men . On 3 separate occasions , subjects were r and omly assigned among 3 treatments : green tea extract ( 50 mg caffeine and 90 mg epigallocatechin gallate ) , caffeine ( 50 mg ) , and placebo , which they ingested at breakfast , lunch , and dinner . RESULTS Relative to placebo , treatment with the green tea extract result ed in a significant increase in 24-h EE ( 4 % ; P < 0.01 ) and a significant decrease in 24-h RQ ( from 0.88 to 0.85 ; P < 0.001 ) without any change in urinary nitrogen . Twenty-four-hour urinary norepinephrine excretion was higher during treatment with the green tea extract than with the placebo ( 40 % , P < 0.05 ) . Treatment with caffeine in amounts equivalent to those found in the green tea extract had no effect on EE and RQ nor on urinary nitrogen or catecholamines . CONCLUSIONS Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se . The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis , fat oxidation , or both
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 ) .