title: Green tea (Camellia sinensis) and cancer prevention: a systematic review of randomized trials and epidemiological studies Does supplementation with green tea extract improve insulin resistance in obese type 2 diabetics? A randomized, double-blind, and placebo-controlled clinical trial. The Effects of Epigallocatechin-3-Gallate on Thermogenesis and Fat Oxidation in Obese Men: A Pilot Study Coffee, tea, and incident type 2 diabetes: the Singapore Chinese Health Study. The Relationship between Green Tea and Total Caffeine Intake and Risk for Self-Reported Type 2 Diabetes among Japanese Adults Coffee Consumption and Risk for Type 2 Diabetes Mellitus Genoprotective effects of green tea (Camellia sinensis) in human subjects: results of a controlled supplementation trial. Coffee consumption and risk of type 2 diabetes mellitus among middle-aged Finnish men and women. 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. Effect of green tea extract on obese women: a randomized, double-blind, placebo-controlled clinical trial. Standardized capsule of Camellia sinensis lowers cardiovascular risk factors in a randomized, double-blind, placebo-controlled study. A green tea extract high in catechins reduces body fat and cardiovascular risks in humans.
abstract: Background Green tea is one of the most popular beverages worldwide . This review summarizes the beneficial effects of green tea on cancer prevention . Methods Electronic data bases , including PubMed ( 1966–2008 ) , the Cochrane Library ( Issue 1 , 2008 ) and Chinese Biomedical Data base ( 1978–2008 ) with supplement of relevant websites , were search ed . There was no language restriction . The search es ended at March 2008 . We included r and omized and non-r and omized clinical trials , epidemiological studies ( cohort and case-control ) and a meta- analysis . We excluded case series , case reports , in vitro and animal studies . Outcomes were measured with estimation of relative risk , hazard or odd ratios , with 95 % confidence interval . Results Forty-three epidemiological studies , four r and omized trials and one meta- analysis were identified . The overall quality of these studies was evaluated as good or moderate . While some evidence suggests that green tea has beneficial effects on gastrointestinal cancers , the findings are not consistent . Conclusion Green tea may have beneficial effects on cancer prevention . Further studies such as large and long term cohort studies and clinical trials are warranted BACKGROUND Green tea is one of the most popular beverages in the world . It is believed to have beneficial effects in the prevention and treatment of many diseases , one of which is type 2 diabetes . The aim of the study is to examine the effect of a decaffeinated green tea extract ( GTE ) providing a daily dose of 856 mg of epigallocatechin gallate ( EGCG ) on obese individuals with type 2 diabetes . MATERIAL S AND METHODS The clinical trial was a r and omized , double-blind , placebo-controlled clinical trial conducted from December 2007 through November 2008 . The subjects were r and omly assigned to either receive 1,500 mg of a decaffeinated GTE or placebo daily for 16 weeks . Sixty-eight of 80 subjects , ages 20 - 65 years with BMI > 25 kg/m2 and type 2 diabetes for more than one year , completed this study .  Homeostasis model assessment for insulin resistance ( HOMA-IR ) was used as the major outcome measurement . At baseline and after 16 weeks of treatment , anthropometric measurements , fasting glucose , hemoglobin A1C percent ( HbA1C ) , hormone peptides , and plasma lipoproteins were measured from both groups . RESULTS No statistically significant differences were detected between the decaffeinated GTE and placebo groups in any measured variable . A statistically significant within-group 0.4-percent reduction in HbA1C ( from 8.4 to 8.0 % ) was observed after GTE treatment compared to baseline . Within-group comparison also revealed that the GTE group had significant reductions in waist circumference ( WC ) , HOMA-IR index , and insulin level , and a significant increase in the level of ghrelin . Within-group comparison of those in the placebo group showed a significant increase in the level of ghrelin . CONCLUSIONS This study found no statistical difference in any measured variable between the decaffeinated GTE and placebo groups ; however , there were some statistically significant within-group changes detected . More research is required to determine whether a decaffeinated GTE st and ardized for EGCG content will provide any clinical benefits in obese individuals with type 2 diabetes . Clinical Trial Registration NO : NCT00567905 Objectives : The development of obesity is characterized by an increase in adipose tissue mass and by concomitant and profound changes in almost all organ functions leading to diseases such as hypertension , diabetes mellitus and coronary heart disease . Recent data from human studies indicate that the consumption of green tea and green tea extracts may help reduce body weight , mainly body fat , by increasing postpr and ial thermogenesis and fat oxidation . However , human studies investigating the metabolic effects of the most predominant tea catechin , EGCG , alone are absent . Methods : In a r and omized double blind , placebo-controlled , cross-over pilot study , six overweight men were given 300 mg EGCG/d for 2d . Fasting and postpr and ial changes in energy expenditure ( EE ) and substrate oxidation were assessed . Results : Resting EE did not differ significantly between EGCG and placebo treatments , although during the first postpr and ial monitoring phase , respiratory quotient ( RQ ) values were significantly lower with EGCG compared to the placebo . Conclusions : These findings suggest that EGCG alone has the potential to increase fat oxidation in men and may thereby contribute to the anti-obesity effects of green tea . However , more studies with a greater sample size and a broader range of age and BMI are needed to define the optimum dose 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 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 Context A recently published study in a Dutch population identified an association between higher coffee consumption and lower risk for type 2 diabetes mellitus  but did not distinguish between intake of regular and decaffeinated coffee . Contribution This large epidemiologic study in a U.S. sample confirmed the Dutch study findings . It also found a statistically significant protective association between total caffeine intake and type 2 diabetes mellitus and a modest inverse association with decaffeinated coffee consumption . Implication s Consumption of caffeinated coffee is associated with a reduced risk for type 2 diabetes mellitus . Further studies should explore the long-term effects of caffeine on glucose metabolism . The Editors The prevalence of type 2 diabetes mellitus has increased dramatically in the past decades , and the disease now affects approximately 8 % of U.S. adults ( 1 ) . Diet and lifestyle factors are primary determinants of risk for type 2 diabetes ( 2 ) . In addition to overweight and obesity , other independent behavioral and lifestyle factors include physical inactivity , smoking , and a diet higher in glycemic load and trans fatty acids and lower in fiber and polyunsaturated fatty acids . Coffee consumption may be related to diabetes because short-term metabolic studies have suggested that caffeine adversely affects insulin sensitivity and glucose metabolism ( 3 ) . Coffee consumption is widespread ; more than 50 % of Americans drink coffee , and average per capita intake is about 2 cups per day ( 4 ) . Coffee is the primary source of caffeine intake , providing approximately 210 mg/d per person in the United States . In humans , acute administration of caffeine decreases insulin sensitivity and impairs glucose tolerance ( 3 , 5 - 8 ) . On the other h and , caffeine stimulates thermogenesis and increases energy expenditure ( 9 - 11 ) , which may facilitate weight reduction and maintenance . Because of these complex physiologic effects of caffeine and because tolerance to the humoral and hemodynamic effects of caffeine typically develops with long-term use ( 12 ) , it is difficult to extrapolate findings from short-term metabolic studies to long-term use of coffee and other caffeinated beverages . A recent epidemiologic study has found a statistically significant inverse association between coffee consumption and risk for type 2 diabetes  in a sample of Dutch participants ( 13 ) . After adjustment for potential confounders , the relative risk for type 2 diabetes among participants consuming at least 7 cups of coffee per day as compared with those consuming 2 cups or less per day was 0.50 ( 95 % CI , 0.35 to 0.72 ; P < 0.001 for trend ) . The study , however , could not distinguish regular coffee from decaffeinated coffee and did not evaluate the association with total caffeine intake . In our study , we examined long-term intake of coffee and other caffeinated beverages and decaffeinated coffee in relation to incidence of type 2 diabetes in 2 large prospect i ve cohorts of men and women . In particular , we examined whether the associations were modified by smoking and body mass index . Methods Study Sample The Health Professionals Follow-up Study The Health Professionals Follow-up Study ( HPFS ) was established in 1986 when 51 529 male health professionals , including dentists , optometrists , veterinarians , osteopathic physicians , podiatrists , and pharmacists , who were 40 to 75 years of age returned a mailed question naire providing detailed information about their medical history , lifestyle , and other risk factors ( 14 ) . Information on the cohort is up date d every 2 years to identify newly diagnosed diseases . For our analysis , we excluded men with a previous diagnosis of type 2 diabetes , coronary heart disease , or cancer at baseline . Participants who did not complete more than 70 of 131 food items in the 1986 dietary question naire or had extreme scores for total daily intake of energy ( < 800 kcal or > 4200 kcal ) were excluded . After exclusions , the analysis included 41 934 eligible men who were followed from 1986 to 1998 . The Nurses ' Health Study The Nurses ' Health Study ( NHS ) was established in 1976 when 121 700 female nurses 30 to 55 years of age living in 11 large states completed a mailed question naire providing detailed information about their medical history , lifestyles , and other risk factors ( 15 ) . The information is up date d every 2 years to identify newly diagnosed diseases . In 1980 , a semiquantitative food frequency question naire was added . For our analysis , we excluded women with a previous diagnosis of type 2 diabetes , coronary heart disease , or cancer at baseline . Participants who did not complete more than 10 items on the 1980 dietary question naire or had extreme scores for total daily intake of energy ( < 500 kcal or > 3500 kcal ) were also excluded , leaving 84 276 eligible women who were followed from 1980 to 1998 . Assessment of Coffee and Caffeine Intake Vali date d dietary question naires were sent to the HPFS participants in 1986 , 1990 , and 1994 and to the NHS participants in 1980 , 1984 , 1986 , 1990 , and 1994 . In all the question naires , participants were asked how often on average during the previous year they had consumed coffee and tea . Decaffeinated coffee and different types of caffeinated soft drinks were first assessed in 1986 in the HPFS and in 1984 in the NHS . We assessed the total intake of caffeine  by summing the caffeine content for a specific amount of each food during the previous year ( 1 cup for coffee or tea , one 12-ounce bottle or can for carbonated beverages , and 1 ounce for chocolate ) multiplied by a weight proportional to the frequency of its use . The participants could choose from 9 frequency responses ( never , 1 to 3 per month , 1 per week , 2 to 4 per week , 5 to 6 per week , 1 per day , 2 to 3 per day , 4 to 5 per day , and 6 or more per day ) . Using the U.S. Department of Agriculture food composition sources , we estimated that the caffeine content was 137 mg per cup of coffee , 47 mg per cup of tea , 46 mg per bottle or can of cola beverage , and 7 mg per serving of chocolate c and y. In our validation studies , high correlations were recorded for coffee and other  caffeinated beverage intake assessed by the food frequency question naire and several 1-week diet records ( coffee , r = 0.78 ; tea , r = 0.93 ; and caffeinated sodas , r = 0.85 ) ( 16 ) . For these analyses , coffee consumption was categorized into 5 groups : never , less than 1 cup per day , 1 to 3 cups per day , 4 to 5 cups per day , and 6 cups or more per day . Caffeine intake was categorized into quintiles . Assessment of Diabetes Cases Participants who reported having diabetes were sent a supplementary mailed question naire that asked about symptoms , diagnostic tests , and treatment . We considered any 1 of the following criteria to represent a new case of diabetes : classic symptoms and elevated glucose levels ( fasting plasma glucose concentration 7.8 mmol/L [ 140 mg/dL ] or r and omly measured concentration 11.1 mmol/L [ 200 mg/dL ] ) ; at least 2 elevated plasma glucose concentrations on different occasions in the absence of symptoms ( plasma glucose level 11.1 mmol/L [ 200 mg/dL ] 2 or more hours after oral glucose tolerance testing ) ; or treatment with oral hypoglycemic agents or insulin . Our criteria for diabetes classification are consistent with those proposed by the National Diabetes Data Group ( 17 ) because most cases were diagnosed before 1997 . The validity of this diagnostic procedure has been verified in a sub sample of this study sample ( 18 ) . The diagnosis of type 2 diabetes was confirmed by medical records in 98 % of the participants . In addition , another sub study assessing the prevalence of undiagnosed diabetes suggested a very low rate of false-negative results ( 19 ) . Statistical Analysis We calculated the follow-up period from the return of the  baseline question naires ( in 1986 for men and in 1980 for women ) to the diagnosis of type 2 diabetes , death , or the end of follow-up ( January 1998 for men and June 1998 for women ) , whichever occurred first . Incidence rates for diabetes were calculated by dividing incident cases by person-years of follow-up in each category of coffee intake .  Relative risks were calculated as the rate of occurrence of type 2 diabetes in each quintile of caffeine intake divided by the corresponding rate in the lowest quintile , and 95 % CIs were calculated . To inspect potential confounding variables for the analyses , we examined baseline characteristics ( directly st and ardized to the age distribution of each cohort ) according to coffee consumption levels . We used proportional hazards models ( 20 ) to adjust for several risk factors , including age in 5 categories ( < 50 , 50 to 54 , 55 to 59 , 60 to 64 , or 65 years of age ) ; body mass index ( weight divided by height [ kg/m2 ] ) in 8 categories ( < 23 , 23 to 24 , 25 to 28 , 29 to 30 , 31 to 32 , 33 to 34 , 35 to 39 , or 40 kg/m2 ) ; physical activity ( hours of moderate or vigorous exercise in NHS or quintiles of metabolic equivalents in HPFS ) ; family history of diabetes ( yes or no ) ; hormone use ( never , current , or past [ in NHS only ] ) ; smoking status ( never , past , or current smokers [ 1 to 14 , 15 to 24 , or 25 cigarettes per day ] ) ; alcohol consumption ( 0 , 0.1 to 4.9 , 5 to 9.9 , 10 to 14.9 , or 15 g/d ) ; total calorie intake ( continuous ) ; and quintiles of trans fat , glycemic load , and cereal fiber intake . We also adjusted for magnesium intake because our previous analyses have shown an inverse association between dietary magnesium and risk for diabetes ( 21 ) . Information on covariates was up date d periodically during follow-up . We performed a test for trend by treating median values of each category of caffeine and coffee intake as continuous variables . To represent long-term intake of coffee and caffeine and to reduce measurement error , we conducted analyses using cumulative up date d caffeine and coffee intake from all question naires ( 22 ) . For example , in the NHS ,  diabetes incidence between 1980 and 1984 was related to the coffee intake from the 1980 Green tea is rich in polyphenolic antioxidants and has widely reported but largely unsubstantiated health benefits . In the present study , genoprotective effects of two types of green tea were studied both in an in vitro and in a human supplementation trial . For the in vitro study , human lymphocytes were pre-incubated in tea ( 0·005 - 0·1 % , w/v ) , washed and subjected to oxidant challenge induced by H2O2 . In a placebo-controlled , cross-over supplementation study , eighteen healthy volunteers took 2 x 150 ml/d of 1 % ( w/v ) green tea ( ' Longjing ' green tea or ' screw-shaped ' green tea ) or water ( control ) for 4 weeks ( n 6 ) . Subjects took all the three treatments in a r and om order , with 6 weeks ' washout between each treatment . Fasting blood and urine were collected before and after each treatment . The comet assay was used to measure the resistance of lymphocytic DNA to H2O2-induced challenge . Basal oxidation-induced DNA damage was measured using the formamidopyrimidine glycosylase ( Fpg ) enzyme-assisted comet assay . Urine 7,8-dihydro-2-deoxyguanosine ( 8-oxodG , mol/mmol creatinine ) , a biomarker of whole-body oxidative stress , was measured by liquid chromatography with t and em MS . In vitro testing results of tea-treated cells showed increased ( P < 0·05 ) resistance of DNA to the challenge . In the supplementation trial , a significant ( P < 0·05 ) increase in resistance was also observed . Furthermore , the FPg comet data showed .20 % decrease in DNA damage  with tea supplementation : mean and st and ard deviation changes in % DNA in comet tail in the Fpg-assisted comet assay were : -5·96 ( SD 3·83 ) % after Longjing tea ; -6·22 ( SD 3·34 ) % after screw-shaped tea ; + 0·91 ( SD 5·79 ) % after water ( P < 0·05 ) . No significant changes in urine 8-oxodG were seen . The results indicate that green tea has significant genoprotective effects and provide evidence for green tea as a ' functional food ' CONTEXT Only a few studies of coffee consumption and  diabetes mellitus ( DM )  have been reported , even though coffee is the most consumed beverage in the world . OBJECTIVE To determine the relationship between coffee consumption and the incidence of  type 2 DM among Finnish individuals , who have the highest coffee consumption in the world . DESIGN , SETTING , AND PARTICIPANTS A prospect i ve study from combined surveys conducted in 1982 , 1987 , and 1992 of 6974 Finnish men and 7655 women aged 35 to 64 years without history of stroke , coronary heart disease , or DM at baseline , with 175 682 person-years of follow-up .  Coffee consumption and other study parameters were determined at baseline using st and ardized measurements . MAIN OUTCOME MEASURES Hazard ratios ( HRs ) for the incidence of type 2 DM were estimated for different levels of daily coffee consumption . RESULTS During a mean follow-up of 12 years , there were 381 incident cases of type 2 DM . After adjustment for confounding factors ( age , study year , body mass index , systolic blood pressure , education , occupational , commuting and leisure-time physical activity , alcohol and tea consumption , and smoking ) , the HRs of DM associated with the amount of coffee consumed daily ( 0 - 2 , 3 - 4 , 5 - 6 , 7 - 9 , > or = 10 cups ) were 1.00 , 0.71 ( 95 % confidence interval [ CI ] , 0.48 - 1.05 ) , 0.39 ( 95 % CI , 0.25 - 0.60 ) , 0.39 ( 95 % CI , 0.20 - 0.74 ) , and 0.21 ( 95 % CI , 0.06 - 0.69 ) ( P for trend<.001 ) in women , and 1.00 , 0.73 ( 95 % CI , 0.47 - 1.13 ) , 0.70 ( 95 % CI , 0.45 - 1.05 ) , 0.67 ( 95 % CI , 0.40 - 1.12 ) , and 0.45 ( 95 % CI , 0.25 - 0.81 ) ( P for trend = .12 ) in men , respectively . In both sexes combined , the multivariate-adjusted inverse association was significant ( P for trend < .001 ) and persisted when stratified by younger and older than 50 years ; smokers and never smokers ; healthy weight , overweight , and obese participants ; alcohol drinker and nondrinker ; and participants drinking filtered and nonfiltered coffee . CONCLUSION Coffee drinking has a grade d inverse association with the risk of type 2 DM ; however , the reasons for this risk reduction associated with coffee remain unclear 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 AIMS To examine the effect of green tea extract ( GTE ) on obese women and to explore the relationship between GTE and obesity-related hormone peptides . METHODS A r and omized , double-blind , placebo-controlled clinical trial was conducted from July 2006 to June 2007 in Taipei Hospital , Taiwan . Seventy-eight of 100 obese women aged between 16 and 60 years with BMI > 27 kg/m(2 ) and who had not received any other weight control maneuvers within the last 3 months completed this study . The subjects were r and omly divided into Groups A and B. Group A ( n=41 ) received GTE while Group B ( n=37 ) took cellulose as a placebo , one capsule ( 400 mg ) three times each day for 12 weeks . The body weight ( BW ) , body mass index ( BMI ) and waist circumflex ( WC ) were measured at the beginning of the study and after 12 weeks of treatment with GTE . The data were compared and expressed as % reduction . RESULTS There was only a 0.3 % reduction in BW ( 0.15 kg ) after 12 weeks of treatment with GTE . There was no statistical difference in % reduction in BW , BMI and WC between the GTE and placebo groups . Within group comparison revealed that the GTE group had significant reduction in LDL-cholesterol and triglyceride , and marked increase in the level of HDL-cholesterol , adiponectin and ghrelin . On the other h and , the placebo group showed significant reduction in triglyceride only , and a marked increase in the level of ghrelin alone . CONCLUSIONS This study showed no statistical difference in % reduction in BW , BMI and WC between the GTE and placebo groups after 12 weeks of treatment . The intake of GTE ( 491 mg catechins containing 302 mg EGCG ) for 12 weeks is considered safe as shown by the results OBJECTIVE Previous studies examining the effect of tea drinking on cardiovascular health have produced mixed results due to their observational nature and qualitatively and quantitatively imprecise definitions of active tea components . The objective of this study was to determine if a st and ardized and defined decaffeinated green tea ( Camellia sinensis ) product lowers blood pressure , serum lipids , oxidative stress , and markers of chronic inflammation . METHODS A r and omized , double-blind , placebo-controlled , parallel study on 111 healthy adult volunteers 21 - 70 y old was performed . We administered a st and ardized capsule of Camellia sinensis compounds ( CSC ) twice a day . Before and after 3 wk , blood pressure , serum lipids , serum amyloid-alpha ( a marker of chronic inflammation ) , and serum malondialdehyde ( a marker of oxidative stress ) were measured . RESULTS After 3 wk , CSC lowered systolic and diastolic blood pressures by 5 and 4 mmHg , respectively . After 3 mo , systolic blood pressure remained significantly lower . CSC  lowered serum amyloid-alpha by 42 % and lowered malondialdehyde by 11.9 % . In men , there were 10- and 9-mg/dL reductions in total and low-density lipoprotein ( LDL ) cholesterol , respectively . In all subjects with a baseline LDL cholesterol level > 99 mg/dL , there was 9 mg/dL lowering of total and LDL cholesterol . Adverse effects were mild and few and not different from placebo . CONCLUSION CSC was effective for decreasing , in as quickly as 3 wk , blood pressure , LDL cholesterol , oxidative stress , and a marker of chronic inflammation , all independent cardiovascular risk factors OBJECTIVE The body fat reducing effect and reduction of risks for cardiovascular disease by a green tea extract ( GTE ) high in catechins was investigated in humans with typical lifestyles . RESEARCH METHODS AND PROCEDURES Japanese women and men with visceral fat-type obesity were recruited for the trial . After a 2-week diet run-in period , a 12-week double-blind parallel multicenter trial was performed , in which the subjects ingested green tea containing 583 mg of catechins ( catechin group ) or 96 mg of catechins ( control group ) per day . R and omization was stratified by gender and body mass index at each medical institution . The subjects were instructed to maintain their usual dietary intake and normal physical activity . RESULTS Data were analyzed using per- protocol sample s of 240 subjects ( catechin  group ; n = 123 , control group ; n = 117 ) . Decreases in body weight , body mass index , body fat ratio , body fat mass , waist circumference , hip circumference , visceral fat area , and subcutaneous fat area were found to be greater in the catechin group than in the control group . A greater decrease in systolic blood pressure ( SBP ) was found in the catechin group compared with the control group for subjects whose initial SBP was 130 mm Hg or higher . Low-density lipoprotein ( LDL ) cholesterol was also decreased to a greater extent in the catechin group . No adverse effect was found . DISCUSSION The continuous ingestion of a GTE high in catechins led to a reduction in body fat , SBP , and LDL cholesterol , suggesting that the ingestion of such an extract contributes to a decrease in obesity and cardiovascular disease risks
target: 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: 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 ) .