the study was conducted between june 2007 and september 2007 , and between december 2007 and february 2008 .
the persons included in the present study were those who participated in a weight loss program at sendai health promotion center ( weight loss program participants ) and the staff of sendai health promotion center ( weight loss program non - participants ) in japan .
the inclusion criteria for the intervention program were ( 1 ) both sexes and ( 2 ) age between 20 and 70 years .
the exclusion criteria were history of diabetes mellitus , cancer , ischemic heart disease , stroke , or renal disease .
the weight loss program was based on exercise program ( exercise guidance , stretching exercise , and strength training ) and nutritional program ( nutritional guidance and cooking practice ) . with a meansd value of 57 g / ml in adiponectin , a minimum sample size of 50 subjects
would be required to detect a difference ( power=70% , two - sided =0.05 ) .
we asked 60 subjects to participate in this study and obtained informed consent from 51 subjects .
the study protocol was reviewed and approved by the ethics committee of tohoku university graduate school of medicine .
we used commercially available catechin - containing beverages ( 500 ml ) . according to the data provided by the manufacturer ,
the high - concentration beverage contained 400 mg catechin and the low - concentration beverage , 100 mg ( table 1 ) .
adherence to the study protocol was confirmed by asking the subjects to return the bottle caps and by reviewing their consumption records .
eligible participants were stratified by sex ( men or women ) and the weight loss program ( participation or non - participation ) , and randomization was conducted by permuted block method using a four - person block .
a total of 51 participants were randomly assigned by an epidemiologist ( nn ) to either the high catechin group ( n=25 ) or the low catechin group ( n=26 ) ( fig .
1 ) . the study participants were asked to stop gt consumption for 2 weeks ( washout period ) , following which they were to start drinking the provided gt beverages everyday for 9 weeks . during the intervention period
, the participants were asked not to drink any other catechin - containing beverage ; other beverages were allowed .
both the catechin - enriched beverages had similar taste and appearance . at the end of the study
components of the test beverages the outcome measures were changes in the adiponectin levels and cvd risk factors : body weight , body mass index ( bmi ) , waist circumference , blood pressure ( bp ) , and levels of total cholesterol ( tc ) , ldl cholesterol ( ldl - c ) , high - density lipoprotein cholesterol ( hdl - c ) , triglyceride ( tg ) , fasting plasma glucose , as well as aspartate aminotransferase ( ast ) , alanine aminotransferase ( alt ) , gamma - glutamyl transpeptidase ( -gtp ) , uric acid ( ua ) , and high - sensitive c - reactive protein ( crp ) .
blood samples were collected into a tube containing ethylenediaminetetraacetic acid ( edta)-2na and a tube containing heparin . serum and plasma samples were obtained by a 10-min centrifugation at 3,000 rpm within 30 min of obtaining the sample .
the samples were then transported frozen to the srl laboratory in hachioji , tokyo , japan , and stored at below 20c until analysis .
serum adiponectin level was determined by enzyme - linked immunosorbent assay ( elisa ; otsuka pharmaceutical , tokyo , japan ) , serum tc level , ceh - cdh - uv method ( sysmex corporation , hyogo , japan ) , serum ldl - c level , liquid selective detergent method ( sekisui medical , tokyo , japan ) , serum hdl - c level , accelerator selective detergent method ( sekisui medical ) , tg level , enzymatic method without endogenous free glycerol ( sekisui medical ) , fasting plasma glucose level , hk - g-6-pdh method ( shino - test , tokyo , japan ) , ast , alt , and -gtp levels , jscc transferable method ( kanto chemical , tokyo , japan ) , ua level , enzymatic method ( sekisui medical ) , and the high - sensitive crp level was assayed by nephelometric immunoassay ( siemens healthcare diagnostics , tokyo , japan ) .
bmi was calculated as body weight ( kg ) divided by squared height ( m2 ) .
bp was measured using a cuff placed on the upper arm of each participant in the sitting position .
nutrition surveys were carried out using a food frequency questionnaire ( excel eiyokun ) ( 21 ) .
comparisons between the two groups were performed by student 's t - test to assess the differences in the biochemical and anthropometric parameters at baseline .
effects of the intervention on serum adiponectin level and other outcome measures were tested using a paired t - test in each group before and after the intervention .
analysis of covariance was used to investigate the significance of the differences in the initial values as well as the net changes after the intervention between the two groups .
we considered the following variables as potential confounders a priori : age at baseline in years ( continuous variable ) , sex , and baseline level of each variable .
in addition , stratified analyses according to weight loss program ( participation or non - participation ) were conducted .
the study was conducted between june 2007 and september 2007 , and between december 2007 and february 2008 .
the persons included in the present study were those who participated in a weight loss program at sendai health promotion center ( weight loss program participants ) and the staff of sendai health promotion center ( weight loss program non - participants ) in japan .
the inclusion criteria for the intervention program were ( 1 ) both sexes and ( 2 ) age between 20 and 70 years .
the exclusion criteria were history of diabetes mellitus , cancer , ischemic heart disease , stroke , or renal disease .
the weight loss program was based on exercise program ( exercise guidance , stretching exercise , and strength training ) and nutritional program ( nutritional guidance and cooking practice ) . with a meansd value of 57 g / ml in adiponectin , a minimum sample size of 50 subjects
would be required to detect a difference ( power=70% , two - sided =0.05 ) .
we asked 60 subjects to participate in this study and obtained informed consent from 51 subjects .
the study protocol was reviewed and approved by the ethics committee of tohoku university graduate school of medicine .
we used commercially available catechin - containing beverages ( 500 ml ) . according to the data provided by the manufacturer ,
the high - concentration beverage contained 400 mg catechin and the low - concentration beverage , 100 mg ( table 1 ) .
adherence to the study protocol was confirmed by asking the subjects to return the bottle caps and by reviewing their consumption records .
eligible participants were stratified by sex ( men or women ) and the weight loss program ( participation or non - participation ) , and randomization was conducted by permuted block method using a four - person block .
a total of 51 participants were randomly assigned by an epidemiologist ( nn ) to either the high catechin group ( n=25 ) or the low catechin group ( n=26 ) ( fig .
1 ) . the study participants were asked to stop gt consumption for 2 weeks ( washout period ) , following which they were to start drinking the provided gt beverages everyday for 9 weeks . during the intervention period
, the participants were asked not to drink any other catechin - containing beverage ; other beverages were allowed .
both the catechin - enriched beverages had similar taste and appearance . at the end of the study
the outcome measures were changes in the adiponectin levels and cvd risk factors : body weight , body mass index ( bmi ) , waist circumference , blood pressure ( bp ) , and levels of total cholesterol ( tc ) , ldl cholesterol ( ldl - c ) , high - density lipoprotein cholesterol ( hdl - c ) , triglyceride ( tg ) , fasting plasma glucose , as well as aspartate aminotransferase ( ast ) , alanine aminotransferase ( alt ) , gamma - glutamyl transpeptidase ( -gtp ) , uric acid ( ua ) , and high - sensitive c - reactive protein ( crp ) .
blood samples were collected into a tube containing ethylenediaminetetraacetic acid ( edta)-2na and a tube containing heparin . serum and plasma samples were obtained by a 10-min centrifugation at 3,000 rpm within 30 min of obtaining the sample .
the samples were then transported frozen to the srl laboratory in hachioji , tokyo , japan , and stored at below 20c until analysis .
serum adiponectin level was determined by enzyme - linked immunosorbent assay ( elisa ; otsuka pharmaceutical , tokyo , japan ) , serum tc level , ceh - cdh - uv method ( sysmex corporation , hyogo , japan ) , serum ldl - c level , liquid selective detergent method ( sekisui medical , tokyo , japan ) , serum hdl - c level , accelerator selective detergent method ( sekisui medical ) , tg level , enzymatic method without endogenous free glycerol ( sekisui medical ) , fasting plasma glucose level , hk - g-6-pdh method ( shino - test , tokyo , japan ) , ast , alt , and -gtp levels , jscc transferable method ( kanto chemical , tokyo , japan ) , ua level , enzymatic method ( sekisui medical ) , and the high - sensitive crp level was assayed by nephelometric immunoassay ( siemens healthcare diagnostics , tokyo , japan ) .
bmi was calculated as body weight ( kg ) divided by squared height ( m2 ) .
bp was measured using a cuff placed on the upper arm of each participant in the sitting position .
nutrition surveys were carried out using a food frequency questionnaire ( excel eiyokun ) ( 21 ) .
comparisons between the two groups were performed by student 's t - test to assess the differences in the biochemical and anthropometric parameters at baseline .
effects of the intervention on serum adiponectin level and other outcome measures were tested using a paired t - test in each group before and after the intervention .
analysis of covariance was used to investigate the significance of the differences in the initial values as well as the net changes after the intervention between the two groups .
we considered the following variables as potential confounders a priori : age at baseline in years ( continuous variable ) , sex , and baseline level of each variable .
differences were accepted as statistically significant at p<0.05 . in addition , stratified analyses according to weight loss program ( participation or non - participation ) were conducted .
all the study participants completed the study ; 95.9% of the tea bottles were consumed in the high catechin group and 97.6% , in the low catechin group .
comparisons of baseline variables between the high- and low catechin groups are shown in table 2 .
the proportion of women was approximately 65% in both the groups . with the exception of the baseline
mean -gtp level , no other variable showed a significant difference between the two groups . 
 
baseline characteristics of participants according to high - catechin group and low - catechin groupa values were expressed as meansd .
p - values with chi - squared test for female ratio and for biochemical parameters , anthropometric parameters , nutrient intake , and energy expenditure , with student 's t - test .
there were significant reductions in total energy intake and carbohydrate intake in any of the groups .
the intake of total fat , total dietary fiber , sodium chloride , and tocopherol was significantly decreased in the low catechin group . however ,
the net change between the groups was not significant . 
  change in nutrient intake and energy expenditure of participants according to high - catechin group and low - catechin group the change in high - catechin group minus the change in low - catechin group .
the net differences were calculated by analysis of covariance . adjusted for age ( in years ) , sex , and individual baseline variables .
after 9 weeks of catechin consumption , the meansd changes from baseline in the adiponectin level were 1.292.77 g / ml in the high catechin group and 1.001.87 g / ml in the low catechin group .
we found no significant difference between the high- and low catechin group with respect to changes in the serum adiponectin level : 0.35 g / ml ( 95% ci : 1.03 , 1.74 ) .
there were significant decreases in the body weight , bmi , and waist circumference in both the groups , but the net change was not significant for any of these variables .
furthermore , there were no significant differences in the net change in other variables as well . 
 
change in serum adiponectin and cardiovascular risk factors of participants according to high - catechin group and low - catechin group the change in high - catechin group minus the change in low - catechin group .
the net differences were calculated by analysis of covariance . adjusted for age ( in years ) , sex , and individual baseline variables . as for the net change in serum adiponectin ,
stratified analyses according to weight loss program ( participation or non - participation ) were conducted ( table 5 ) . among weight loss program participants and weight loss program non - participants ,
there were no significant differences in the net change : 0.15 g / ml ( 95% ci : 1.54 , 1.85 ) among weight loss program participants , and 1.49 g / ml ( 95% ci : 0.46 , 3.43 ) among weight loss program non - participants . 
 
change in serum adiponectin of participants according to high - catechin group and low - catechin group stratified by weight - loss program the change in high - catechin group minus the change in low - catechin group .
the net differences were calculated by analysis of covariance . adjusted for age ( in years ) , sex , and baseline serum adiponectin .
in this rct , we tested a hypothesis that consumption of catechin - enriched gt would affect the serum adiponectin level and cvd risk factors in apparently healthy subjects .
after 9 weeks of catechin consumption , the meansd changes from baseline in the adiponectin level were significantly increased in both groups . however , we found no significant difference between the high- and low catechin group with respect to changes in the serum adiponectin level : 0.35 g / ml ( 95% ci : 1.03 , 1.74 ) .
the cvd risk factors , namely , body weight , bmi , and waist circumference , were significantly decreased in both the groups , but the net change was not significant for any of these variables .
there are at least three reasons that the changes from baseline in the adiponectin level were significantly increased in the both groups .
first , more than half of the study participants participated in a weight loss program .
third , catechin was contained not only in high - concentration beverage ( high catechin group ; 400 mg ) but also in low - concentration beverage ( low catechin group ; 100 mg ) .
therefore , if the low concentration of the catechins might be enough to increase the adiponectin levels , an increase would be observed in the both groups .
in addition , we conducted stratified analyses according to weight loss program ( participation or non - participation ) because the change in adiponectin levels in both the groups may be related to the significant weight loss program .
we also found that there were no significant differences in the net change among weight loss program participants and non - participants . because the net change among weight loss program non - participants was greater than that among weight loss program participants , the change in adiponectin levels would be less affected by the weight loss program . to date , three rcts have examined the association between tea catechin consumption and adiponectin levels in humans ( 1820 ) .
these rcts recruited patients with diabetes mellitus and obesity . because these patients might have had atherosclerosis before the study , the effect of tea catechin consumption on serum adiponectin level might not be well detected .
observed a change in the adiponectin level after the consumption of 900 ml of water containing 9 g of gt daily for 4 weeks in patients with type 2 diabetes mellitus ( 18 ) .
after 4 weeks , the meansd change in the adiponectin level from the baseline value was 6.033.71 g / ml in intervention group and 6.013.16 g / ml in control group , although the net change between the groups was not significant .
hsu et al . observed a significant increase in the adiponectin level in obese women who consumed one capsule containing 491 mg of total catechin daily ( 19 ) .
after 12 weeks , the meansd change in the adiponectin level from the baseline value was 2.54.2 g / ml in intervention group and 2.05.4 g / ml in control group , although the net change was not significantly different .
observed a significant increase in the adiponectin level after the consumption of 582.8 mg of catechin daily in patients with type 2 diabetes mellitus ( 20 ) .
after 12 weeks , the meansd change in the adiponectin level from the baseline value was 1.320.61 mg / ml in intervention group and 0.340.48 g / ml in control group , although the net change was not significantly different .
thus , all the three rcts showed that the increase in the serum adiponectin level in the intervention group was greater than that in the control group , although the net change between the groups was not significant .
although we recruited healthy participants who did not have a history of diabetes mellitus , cancer , ischemic heart disease , stroke , or renal disease , our findings were consistent with those of the above reports .
although we found no significant difference in the net change in adiponectin level , several reasons should be considered in the interpretation of our results .
first , it may be necessary to consider the difference in the catechin dose between the high- and low catechin groups and the intervention period . in the present study ,
the difference in the catechin dose between the high- and low catechin groups was only 300 mg / day and the intervention period was 9 weeks .
hsu et al . adopted the difference in the catechin dose of 491 mg / day and intervention period of 12 weeks , but the net change in adiponectin level was not significant ( 19 ) .
also , nagao et al . adopted the difference in the catechin dose of 486.5 mg / day and intervention period of 12 weeks , but the net change in adiponectin level was not significant ( 20 ) .
therefore , the difference in the catechin dose and the intervention period could not explain our observation .
second , because gt is consumed primarily in japan and china ( 22 ) , habitual gt consumption may have the potential to affect study results .
although we adopted the washout period for 2 weeks , we did not find any apparent association between catechin - enriched gt consumption and adiponectin .
similarly , previous studies adopted the washout period for 2 weeks ( 19 ) and 4 weeks ( 20 ) , but the net change in adiponectin level was not significant .
also excluded subjectswho had consumed gt regularly for over a month , but the net change in adiponectin level was not significant ( 18 ) .
third , the compounds such as caffeine found in gt may have been responsible for the association between gt consumption and cvd risk factors .
a previous observational study indicated the association between consumption of caffeine - containing coffee and adiponectin .
no association between consumption of caffeine - containing coffee and adiponectin was indicated in either group ( quartile 1 : 0100 mg , quartile 2 : 101237 mg , quartile 3 : 237378 mg , quartile 4 : 379967 mg ) among non - diabetic subjects ( 23 ) . because the difference in the caffeine dose between the high- and low catechin groups was small ( 25 mg / day ) in our study
fourth , chocolate , red wine , apples , and berries are known as good source of catechin ( 24 , 25 ) . although we asked participants not to drink any other catechin - containing beverage , we had no information on the intake of these food items during the 9 weeks .
in addition , we had no data on the levels of the major dietary catechins ( gallocatechin , epicatechin , epigallocatechin , etc . ) and the total blood antioxidant levels .
however , these factors may be divided equally between the high- and low catechin groups by successful randomization .
also , a previous study indicated that the half - lives of epigallocatechin-3-gallate , epigallocatechin , and epicatechin once ingested were 3.4 , 1.7 , and 2.0 h , respectively ( 26 ) .
therefore , it is difficult to interpret the results of all - night fasting plasma levels of catechins , if measured .
finally , our rct design might yield a relatively small number of participants , although we made a power calculation regarding sample size .
we found no significant difference between the high- and low catechin groups with respect to changes in the serum adiponectin level .
our study had a similar sample size to previous rcts , and our results were consistent with results of previous rcts ( 19 , 20 ) .
therefore , a larger sample size may be necessary to detect any effect of tea catechin consumption on serum adiponectin level .
we found no significant differences in cvd risk factors between the high- and low catechin groups .
many studies have assessed the relation between gt consumption and cvd risk factors . in previous studies ,
the gt consumption showed statistically significant reductions in body weight , bmi , and waist circumference ( 2729 ) .
our study showed that decrease in the anthropometric parameters in the high catechin group was greater than that in the low catechin group , although the net change between groups was not significant . the previous studies that suggested statistically significant changes had a larger sample size ( 28 , 29 ) .
therefore , a larger sample size may be necessary to detect the effect of tea catechin consumption on the anthropometric parameters .
the effect of gt consumption on bp has been investigated in meta - analysis of previous studies .
these data suggested that gt consumption did not show significant effects on systolic and diastolic bp ( 30 ) .
our results on bp were consistent with the previous studies . among previous studies that have examined the association between gt and blood cholesterol ( tc , ldl - c , and hdl - c ) ,
gt consumption significantly lowered the tc and ldl - c level , but no effect on hdl - c was observed ( 20 , 28 , 30 , 31 ) . our results on hdl - c were consistent with previous studies , but the inconsistent findings on the effect of gt consumption on tc and ldl - c were observed .
there are several possible reasons for the discrepancy between our study and previous studies on tc and ldl - c .
first , the subjects of the previous studies were not a healthy population ( 20 ) .
therefore , one of the reasons for discrepancy might be explained by the difference in the study subjects .
this rct showed that increase in serum adiponectin level in the high catechin group was greater than that in the low catechin group , although the net change between groups was not significant .
also , no significant difference was observed between the high- and low catechin groups with respect to changes in any cvd risk factors .
this study was supported by a grant - in - aid for exploratory research ( term of project : 20072008 , project number : 19659157 ) from the japan society for the promotion of science ( jsps ) , japan .
 backgroundprevious observational studies have indicated that green tea ( gt ) consumption is associated with reduced mortality from cerebral infarction but not with mortality from cerebral hemorrhage . therefore , we hypothesized that gt exerts a direct antiatherosclerotic effect without any effect on hypertension . to investigate this hypothesis , we focused on adiponectin that seems to be among the several key players in atherosclerosis.objectivethe objective of this randomized controlled trial ( rct ) was to assess whether the consumption of catechin - enriched gt affects serum adiponectin levels and cardiovascular disease ( cvd ) risk factors among apparently healthy subjects.designa total of 51 individuals participated in the study . 
 eligible participants were randomly assigned into gt consumption groups with either high catechin ( 400 mg / day ) or low catechin ( 100 mg / day ) . 
 the study participants were asked to stop gt consumption for 2 weeks ( washout period ) , following which they were to start drinking the provided gt beverages everyday for 9 weeks . 
 the outcome measures were changes in the adiponectin levels and cvd risk factors ( body weight , body mass index , waist circumference , blood pressure , total cholesterol , low - density lipoprotein cholesterol , high - density lipoprotein cholesterol , triglyceride , fasting plasma glucose , as well as aspartate aminotransferase , alanine aminotransferase , gamma - glutamyl transpeptidase , uric acid , and high - sensitive c - reactive protein).resultsafter intervention for 9 weeks , we found no significant difference between the high- and low catechin group with respect to changes in the serum adiponectin level : 0.35 g / ml ( 95% confidence interval ( ci ) : 1.03 , 1.74 ) . 
 also , no significant difference was observed between the high- and low catechin groups with respect to changes in any of the measured cvd risk factors.conclusionthis rct showed no significant difference between the high- and low catechin groups with respect to changes in the serum adiponectin level and any cvd risk factors . 