Randomized controlled trial for an effect of green tea-extract powder supplementation on glucose abnormalities

A Systematic Review and Meta-Analysis of the Effects of Flavanol-Containing Tea, Cocoa and Apple Products on Body Composition and Blood Lipids: Exploring the Factors Responsible for Variability in Their Efficacy

Several randomized controlled trials (RCTs) and meta-analyses support the benefits of flavanols on cardiometabolic health, but the factors affecting variability in the responses to these compounds have not been properly assessed. The objectives of this meta-analysis were to systematically collect the RCTs-based-evidence of the effects of flavanol-containing tea, cocoa and apple products on selected biomarkers of cardiometabolic risk and to explore the influence of various factors on the variability in the responses to the consumption of these products. A total of 120 RCTs were selected. Despite a high heterogeneity, the intake of the flavanol-containing products was associated using a random model with changes (reported as standardized difference in means (SDM)) in body mass index (−0.15, p < 0.001), waist circumference (−0.29, p < 0.001), total-cholesterol (−0.21, p < 0.001), LDL-cholesterol (−0.23, p < 0.001), and triacylglycerides (−0.11, p = 0.027), and with an increase of HDL-cholesterol (0.15, p = 0.005). Through subgroup analyses, we showed the influence of baseline-BMI, sex, source/form of administration, medication and country of investigation on some of the outcome measures and suggest that flavanols may be more effective in specific subgroups such as those with a BMI ≥ 25.0 kg/m², non-medicated individuals or by specifically using tea products. This meta-analysis provides the first robust evidence of the effects induced by the consumption of flavanol-containing tea, cocoa and apple products on weight and lipid biomarkers and shows the influence of various factors that can affect their bioefficacy in humans. Of note, some of these effects are quantitatively comparable to those produced by drugs, life-style changes or other natural products. Further, RCTs in well-characterized populations are required to fully comprehend the factors affecting inter-individual responses to flavanol and thereby improve flavanols efficacy in the prevention of cardiometabolic disorders.

Nutritional intervention and impact of polyphenol on glycohemoglobin (HbA1c) in non-diabetic and type 2 diabetic subjects: Systematic review and meta-analysis

Polyphenols have been extensively studied for their antioxidant and anti-inflammatory properties. Recently, their antiglycative actions by oxidative stress modulation have been linked to the prevention of diabetes and associated complications. This article assesses the evidence for polyphenol interventions on glycohemoglobin (HbA1c) in non-diabetic, pre-diabetic, and type 2 diabetes mellitus (T2DM) subjects. A systematic review of polyphenols' clinical trials on HbA1c in humans was performed according to the Preferred Reporting Items for Systematic Review and Meta-Analysis. Thirty-six controlled randomized trials with HbA1c values were included. Polyphenols (extracts, supplements, and foods) were supplemented (28 mg to 1.5 g) for 0.7 to 12 months. Combining all subjects (n = 1954, mean baseline HbA1c = 7.03%, 53 mmol/mol), polyphenol supplementation significantly (P < 0.001) lowered HbA1c% by -0.53 ± 0.12 units (-5.79 ± 0.13 mmol/mol). This reduction was significant (P < 0.001) in T2DM subjects, specifically (n = 1426, mean baseline HbA1c = 7.44%, 58 mmol/mol), with HbA1c% lowered by -0.21 ± 0.04 units (-2.29 ± 0.4 mmol/mol). Polyphenol supplementation had no significant effect (P > 0.21) in the non-diabetic (n = 258, mean baseline HbA1c = 5.47%, 36 mmol/mol) and the pre-diabetic subjects (n = 270, mean baseline HbA1c = 6.06%, 43 mmol/mol) strata: -0.39 ± 0.27 HbA1c% units (-4.3 ± 0.3 mmol/mol), and -0.38 ± 0.31 units (-4.2 ± 0.31 mmol/mol), respectively. In conclusion, polyphenols can successfully reduce HbA1c in T2DM without any intervention at glycemia, and could contribute to the prevention of diabetes complications.

Functional Characterization of Tea (Camellia sinensis) MYB4a Transcription Factor Using an Integrative Approach

Green tea (Camellia sinensis, Cs) abundantly produces a diverse array of phenylpropanoid compounds benefiting human health. To date, the regulation of the phenylpropanoid biosynthesis in tea remains to be investigated. Here, we report a cDNA isolated from leaf tissues, which encodes a R2R3-MYB transcription factor. Amino acid sequence alignment and phylogenetic analysis indicate that it is a member of the MYB4-subgroup and named as CsMYB4a. Transcriptional and metabolic analyses show that the expression profile of CsMYB4a is negatively correlated to the accumulation of six flavan-3-ols and other phenolic acids. GFP fusion analysis shows CsMYB4a's localization in the nucleus. Promoters of five tea phenylpropanoid pathway genes are isolated and characterized to contain four types of AC-elements, which are targets of MYB4 members. Interaction of CsMYB4a and five promoters shows that CsMYB4a decreases all five promoters' activity. To further characterize its function, CsMYB4a is overexpressed in tobacco plants. The resulting transgenic plants show dwarf, shrinking and yellowish leaf, and early senescence phenotypes. A further genome-wide transcriptomic analysis reveals that the expression levels of 20 tobacco genes involved in the shikimate and the phenylpropanoid pathways are significantly downregulated in transgenic tobacco plants. UPLC-MS and HPLC based metabolic profiling reveals significant reduction of total lignin content, rutin, chlorogenic acid, and phenylalanine in CsMYB4a transgenic tobacco plants. Promoter sequence analysis of the 20 tobacco genes characterizes four types of AC-elements. Further CsMYB4a-AC element and CsMYB4a-promoter interaction analyses indicate that the negative regulation of CsMYB4a on the shikimate and phenylpropanoid pathways in tobacco is via reducing promoter activity. Taken together, all data indicate that CsMYB4a negatively regulates the phenylpropanoid and shikimate pathways. Highlight: A tea (Camellia sinensis) MYB4a is characterized to encode a R2R3-MYB transcription factor. It is shown to repressively control the phenylpropanoid and shikimate pathway.

Pleiotropic effects of acarbose on atherosclerosis development in rabbits are mediated via upregulating AMPK signals

Acarbose, an α-glucosidase inhibitor, is reported to reduce the incidence of silent myocardial infarction and slow the progression of intima-media thickening in patients with glucose intolerance. Here we investigate other impacts of acarbose on atherosclerosis development and the underlying mechanisms of atherosclerosis initiation and progression in vivo and in vitro. Rabbits fed a high cholesterol diet (HCD) were treated with acarbose (2.5-5.0 mg kg^-1). Immunohistochemistry was used to assess the expression of inducible nitric oxide synthase (iNOS), Ras, proliferating cell nuclear antigen (PCNA), IL-6, β-galactosidase, and p-AMPK in atherosclerotic lesions. Treatment with acarbose in HCD-fed rabbits was found to significantly reduce the severity of aortic atheroma and neointimal expression of α-actin, PCNA, IL-6, TNF-α, Ras, and β-galactosidase; to significantly increase expression of iNOS and p-AMPK, but not to affect serum levels of glucose, total cholesterol, and LDL. Western blot analysis showed acarbose dose-dependently decreased β-galactosidase and Ras expression and increased p-AMPK expression in TNF-α-treated A7r5 cells. In addition, acarbose restored p-AMPK and iNOS levels in AMPK inhibitor- and iNOS inhibitor-treated A7r5 cells, respectively. In conclusion, acarbose can pleiotropically inhibit rabbit atherosclerosis by reducing inflammation, senescence, and VSMCs proliferation/migration via upregulating AMPK signals.

Effects of green tea catechin extract on serum lipids in postmenopausal women: a randomized, placebo-controlled clinical trial

BACKGROUND

Green tea has been suggested to improve cardiovascular disease risk factors, including circulating lipid variables. However, current evidence is predominantly based on small, short-term randomized controlled trials conducted in diverse populations.

OBJECTIVE

The aim of this study was to examine the efficacy and impact of green tea extract (GTE) supplementation high in epigallocatechin gallate (EGCG) on blood lipids in healthy postmenopausal women.

DESIGN

This was an ancillary study of a double-blind, randomized, placebo-controlled, parallel-arm trial investigating the effects of a GTE supplement containing 1315 mg catechins (843 mg EGCG) on biomarkers of breast cancer risk. Participants were randomly assigned to receive GTE (n = 538) or placebo (n = 537) and were stratified by catechol-O-methyltransferase (COMT) genotype activity (high COMT compared with low or intermediate COMT genotype activity). They consumed either 4 GTE or identical placebo capsules daily for 12 mo. A total of 936 women completed this substudy. Circulating lipid panels including total cholesterol (TC), HDL cholesterol, and triglycerides were measured at baseline and at months 6 and 12.

RESULTS

Compared with placebo, 1-y supplementation with GTE capsules resulted in a significant reduction in circulating TC (-2.1% compared with 0.7%; P = 0.0004), LDL cholesterol (-4.1% compared with 0.9%; P < 0.0001) and non-HDL cholesterol (-3.1% compared with 0.4%; P = 0.0032). There was no change in HDL-cholesterol concentration, but triglyceride concentrations increased by 3.6% in the GTE group, whereas they decreased by 2.5% in the placebo group (P = 0.046). A significant reduction in TC was observed only among women with high (i.e., ≥200 mg/dL) baseline TC concentrations (P-interaction = 0.01) who consumed GTE capsules. The effect of GTE on the increase in triglycerides was mainly observed among obese women and statin users (P-interaction = 0.06).

CONCLUSION

Supplementation with GTE significantly reduced circulating TC and LDL-cholesterol concentrations, especially in those with elevated baseline TC concentrations. This trial was registered at clinicaltrials.gov as NCT00917735.

Physiological effects of epigallocatechin-3-gallate (EGCG) on energy expenditure for prospective fat oxidation in humans: A systematic review and meta-analysis

Green tea catechins (GTCs) are known to improve fat oxidation (FOX) during fasted, rested and exercise conditions wherein epigallocatechin-3-gallate (EGCG) is thought to be the most pharmacologically active and has been studied extensively. From the available data of randomized controlled trials (RCTs) on EGCG, we carried out a systematic review and meta-analysis to elucidate whether EGCG consumption indeed increase energy expenditure (EE) and promote FOX. A systematic review of the literature was conducted using electronic databases (PubMed, Embase, Cochrane Library, CINAHL, JICST, JSTPLUS, and JMEDPLUS and others) and eight RCTs were included. RCTs were reviewed using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and methodological quality was assessed. After data extraction, results were aggregated using fixed- and random-effect approaches and expressed to quantify the relationship between the dose of EGCG for respiratory quotient (RQ), EE and rate of FOX to compare the EGCG and placebo treatments. The meta-analysis results of verities of studies in terms of dose and length of duration revealed that EGCG supplementation provided significant mean difference (MD) when compared with placebo for RQ [MD: -0.02; 95% confidence intervals (95% CI), -0.04 to 0.00; I²=67%; P=.01] and EE [MD: 158.05 kJ/day; 95% CI, 4.72 to 311.38; I²=0%; P=.04] in fixed-effect approach. Changes in FOX did not reach the level of statistical significance. Meta-analyses of EGCG influence on the body mass index, waist circumference and total body fat mass (TBFM) were also examined and their impact on the promotion of FOX is reported. Effect of EGCG doses was also systematically reviewed. Finding showed that EGCG intake moderately accelerates EE and reduces RQ. The analyses revealed that the EGCG resulted in difference in RQ and EE but the effect on the other measures of energy metabolism was relatively mild. Possibly, EGCG alone has the potential to increase metabolic rate at 300 mg dose. Collectively, the outcome supports the findings that EGCG has an effect on metabolic parameters. However, the large prospective trials are needed to confirm the findings.

The Powdering Process with a Set of Ceramic Mills for Green Tea Promoted Catechin Extraction and the ROS Inhibition Effect

For serving green tea, there are two prominent methods: steeping the leaf or the powdered leaf (matcha style) in hot water. The purpose of the present study was to reveal chemical and functional differences before and after the powdering process of green tea leaf, since powdered green tea may contribute to expanding the functionality because of the different ingesting style. In this study, we revealed that the powdering process with a ceramic mill and stirring in hot water increased the average extracted concentration of epigallocatechin gallate (EGCG) by more than three times compared with that in leaf tea using high-performance liquid chromatography (HPLC) and liquid chromatography-tandem mass Spectrometry (LC-MS/MS) analyses. Moreover, powdered green tea has a higher inhibition effect of reactive oxygen species (ROS) production in vitro compared with the same amount of leaf tea. Our data suggest that powdered green tea might have a different function from leaf tea due to the higher catechin contents and particles.

Effects of tea or tea extract on metabolic profiles in patients with type 2 diabetes mellitus: a meta-analysis of ten randomized controlled trials

As consumption of tea has been confirmed as a protective factor for type 2 diabetes mellitus (T2DM), it would be interesting to know if T2DM patients could benefit from tea. Because of small sample sizes and inconsistent results of previous studies, we performed this meta-analysis to reevaluate the effects of tea or tea extract on all available outcomes in patients with T2DM. We systematically searched electronic databases of PubMed, Cochrane Library and EMBASE to identify randomized controlled trials of tea in T2DM patients up to January 2015. Weight mean differences for the changes in all outcomes were pooled by Review Manager 5.2 (Cochrane Collaboration, Oxford, England). A total of ten trials including 608 subjects were identified. The meta-analysis found that tea could alleviate the decrease of fasting blood insulin [1.30 U/L, 95% CI (0.36, 2.24)], and reduced waist circumference only in more than 8-week intervention [-2.70 cm, 95% CI (-4.72, -0.69)], whereas there were no statistically significant differences with regard to homeostasis model of insulin resistance 0.38 (-0.18, 0.95), fasting blood glucose -0.05 mmol/L (-0.51, 0.40), low density lipoprotein-cholesterol 0.07 mmol/L (-0.15, 0.29), high density lipoprotein-cholesterol 0.01 mmol/L (-0.08, 0.09), body mass index -0.15 kg/m(2) (-0.50, 0.21), SBP 0.35 mmHg (-3.54, 4.24), DBP -1.02 mmHg (-3.53, 1.48), triglycerides -0.11 mmol/L (-0.28, 0.05) and fasting cholesterol -0.05 mmol/L (-0.20, 0.11) in patients with T2DM, and leptin, ADPN, CRE and UA were also non-significant. The intervention of tea or tea extraction could maintain a stable fasting blood insulin and reduce waist circumference in the T2DM patients; however, the effects on other outcomes were not significant. Copyright © 2015 John Wiley & Sons, Ltd.

Mechanisms of body weight reduction and metabolic syndrome alleviation by tea

Tea, a popular beverage made from leaves of the plant Camellia sinensis, has been shown to reduce body weight, alleviate metabolic syndrome, and prevent diabetes and cardiovascular diseases in animal models and humans. Such beneficial effects have generally been observed in most human studies when the level of tea consumption was three to four cups (600-900 mg tea catechins) or more per day. Green tea is more effective than black tea. In spite of numerous studies, the fundamental mechanisms for these actions still remain unclear. From a review of the literature, we propose that the two major mechanisms are: (i) decreasing absorption of lipids and proteins by tea constituents in the intestine, thus reducing calorie intake; and (ii) activating AMP-activated protein kinase by tea polyphenols that are bioavailable in the liver, skeletal muscle, and adipose tissues. The relative importance of these two mechanisms depends on the types of tea and diet consumed by individuals. The activated AMP-activated protein kinase would decrease gluconeogenesis and fatty acid synthesis and increase catabolism, leading to body weight reduction and metabolic syndrome alleviation. Other mechanisms and the health relevance of these beneficial effects of tea consumption remain to be further investigated.

Effect of tea on blood pressure for secondary prevention of cardiovascular disease: a systematic review and meta-analysis of randomized controlled trials

CONTEXT

Tea has been proposed as an antihypertensive agent for individuals with elevated blood pressure, yet the evidence for this has not been systematically reviewed to date.

OBJECTIVE

The aim of this review was to evaluate the effects of tea on blood pressure in individuals within the prehypertensive and hypertensive blood pressure ranges.

DATA SOURCES

The CENTRAL, PubMed, Embase, and Web of Science databases were searched for all relevant studies published from 1946 to September 27, 2013.

STUDY SELECTION

The selection criteria included randomized controlled trials of adults whose blood pressure was within hypertensive or prehypertensive ranges and in which the applied intervention was green or black tea; controls consisting of placebo, minimal tea intervention, or no intervention; and a follow-up period of at least 2 months.

DATA EXTRACTION

Two reviewers independently extracted data on participants, interventions, comparators, outcomes, and study design. Mean differences (MDs) and 95% confidence intervals (95%CIs) were pooled to generate summary effect estimates.

RESULTS

Meta-analyses of 10 trials (834 participants) showed statistically significant reductions in systolic blood pressure (MD -2.36 mmHg, 95%CI -4.20 to -0.52) and diastolic blood pressure (MD -1.77 mmHg, 95%CI -3.03 to -0.52) with tea consumption.

CONCLUSIONS

Consumption of green or black tea can reduce blood pressure in individuals within prehypertensive and hypertensive ranges, although further investigation with studies of longer duration and stronger methodological quality is warranted to confirm these findings.

Activities of Tannins – from in Vitro Studies to Clinical Trials

Tannins are considered as valuable plant secondary metabolites providing many benefits for human health. In this review information was gathered about bioactivity in vitro and in vivo, as well as about conducted clinical trials. The literature research was based on ScienceDirect, Scopus, and Cochrane databases and presents a wide range of tested activities of tannins. The described clinical trials verify laboratory tests and show the effective health benefits taken from supplementation with tannins.

A combination of isolated phytochemicals and botanical extracts lowers diastolic blood pressure in a randomized controlled trial of hypertensive subjects

BACKGROUND/OBJECTIVES

Isolated phytochemicals have been shown to reduce blood pressure; however, combinations of phytochemicals have rarely been tested in humans. We hypothesized that a combination of extracts from grape seed and skin (330 mg), green tea (100 mg), resveratrol (60 mg) and a blend of quercetin, ginkgo biloba and bilberry (60 mg) would reduce blood pressure (BP) in hypertensive subjects.

SUBJECTS/METHODS

Eighteen individuals meeting BP requirements (⩾130 mm Hg systolic or ⩾85 mm Hg diastolic) and criteria for metabolic syndrome were enrolled in a double-blinded, placebo-controlled, crossover trial (ClinicalTrials.gov, NCT01106170). The 28-day placebo and supplement arms were separated by a 2-week washout period, and 14 -h daytime ambulatory BP was assessed at baseline and at the end point of each arm.

RESULTS

BP was not altered after placebo. After supplement treatment, diastolic pressure was reduced by 4.4 mm Hg (P=0.024, 95% CI, 0.6-8.1), systolic pressure was unchanged and mean arterial pressure trended (P=0.052) toward reduction. Serum angiotensin-converting enzyme activity was similar between placebo and supplement arms, but urinary nitrate and nitrite concentrations were significantly increased (P=0.022) after supplementation. Human aortic endothelial cells treated with metabolites of the polyphenols used in the human supplement trial had a significant increase (P=0.005) in insulin-stimulated eNOS phosphorylation and greater (P<0.001) accumulation of nitrates/nitrites.

CONCLUSIONS

Our clinical and in vitro data support the theory that this combination of polyphenols reduced diastolic pressure by potentiating eNOS activation and nitric oxide production. Such supplements may have clinical relevance as stand-alone or adjunct therapy to help reduce BP.

Interaction mechanism between green tea extract and human α-amylase for reducing starch digestion

This study evaluated the inhibitory effects of the green tea extract on human pancreatic α-amylase activity and its molecular mechanism. The green tea extract was composed of epicatechin (59.2%), epigallocatechin gallate (14.6%) and epicatechin gallate (26.2%) as determined by HPLC analysis. Enzyme activity measurement showed that % inhibition and IC50 of the green tea extract (10%, based on starch) were 63.5% and 2.07 mg/ml, respectively. The Michaelis-Menten constant remained unchanged but the maximal velocity decreased from 0.43 (control) to 0.07 mg/(ml × min) (4 mg/ml of the green tea extract), indicating that the green tea extract was an effective inhibitor against α-amylase with a non-competitive mode. The fluorescence data revealed that the green tea extract bound with α-amylase to form a new complex with static quenching mechanism. Docking study showed the epicatechin gallate in the green tea extract presented stronger affinity than epigallocatechin gallate, with more number of amino acid residues involved in amylase binding with hydrogen bonds and Van der Waals forces. Thus, the green tea extract could be used to manipulate starch digestion for potential health benefits.

Effect of green tea consumption on blood pressure: a meta-analysis of 13 randomized controlled trials

The studies investigating the effects of green tea on blood pressure (BP) have generated inconsistent results. The aim of this study is to quantitatively evaluate the effects of green tea on BP control. PubMed, Embase, and the Cochrane Library (updated to March 2014) were searched for randomized controlled trials evaluating the effects of green tea on BP. Pooled effect of green tea consumption on BP was evaluated using fixed-effects or random-effects model. Thirteen trials comprising a total of 1,367 subjects were included in the current meta-analysis. The overall outcome of the meta-analysis suggested that green tea consumption significantly decrease systolic blood pressure (SBP) level by −1.98 mmHg (95% CI: −2.94, −1.01 mmHg; P < 0.001). Compared with the control group, green tea also showed a significant lowering effect on diastolic blood pressure (DBP) in treatment group (−1.92 mmHg; 95% CI: −3.17, −0.68 mmHg; P = 0.002). Subgroup analyses further suggested that the positive effect of green tea polyphenols on BP was only showed in studies using a low-dose green tea polyphenol, with the long-term intervention duration or ruling out the confounding effects of caffeine. The meta-analysis suggested that green tea consumption had a favorable effect on decrease of BP.

Effects of tea intake on blood pressure: a meta-analysis of randomised controlled trials

The effect of tea intake on blood pressure (BP) is controversial. We performed a meta-analysis of randomised controlled trials to determine the changes in systolic and diastolic BP due to the intake of black and green tea. A systematic search was conducted in MEDLINE, EMBASE and the Cochrane Controlled Trials Register up to May 2014. The weighted mean difference was calculated for net changes in systolic and diastolic BP using fixed-effects or random-effects models. Previously defined subgroup analyses were performed to explore the influence of study characteristics. A total of twenty-five eligible studies with 1476 subjects were selected. The acute intake of tea had no effects on systolic and diastolic BP. However, after long-term tea intake, the pooled mean systolic and diastolic BP were lower by - 1·8 (95 % CI - 2·4, - 1·1) and - 1·4 (95 % CI - 2·2, - 0·6) mmHg, respectively. When stratified by type of tea, green tea significantly reduced systolic BP by 2·1 (95 % CI - 2·9, - 1·2) mmHg and decreased diastolic BP by 1·7 (95 % CI - 2·9, - 0·5) mmHg, and black tea showed a reduction in systolic BP of 1·4 (95 % CI - 2·4, - 0·4) mmHg and a decrease in diastolic BP of 1·1 (95 % CI - 1·9, - 0·2) mmHg. The subgroup analyses showed that the BP-lowering effect was apparent in subjects who consumed tea more than 12 weeks (systolic BP - 2·6 (95 % CI - 3·5, - 1·7) mmHg and diastolic BP - 2·2 (95 % CI - 3·0, - 1·3) mmHg, both P< 0·001). The present findings suggest that long-term ( ≥ 12 weeks) ingestion of tea could result in a significant reduction in systolic and diastolic BP.

The effect of green tea on blood pressure and lipid profile: a systematic review and meta-analysis of randomized clinical trials

INTRODUCTION

Many different dietary supplements are currently marketed for the management of hypertension, but the evidence for effectiveness is mixed. The aim of this systematic review was to evaluate the evidence for or against the effectiveness of green tea (Camellia sinensis) on blood pressure and lipid parameters.

METHODS AND RESULTS

Electronic searches were conducted in Medline, Embase, Amed, Cinahl and the Cochrane Library to identify relevant human randomized clinical trials (RCTs). Hand searches of bibliographies were also conducted. The reporting quality of included studies was assessed using a checklist adapted from the CONSORT Statement. Two reviewers independently determined eligibility, assessed the reporting quality of the included studies, and extracted the data. As many as 474 citations were identified and 20 RCTs comprising 1536 participants were included. There were variations in the designs of the RCTs. A meta-analysis revealed a significant reduction in systolic blood pressure favouring green tea (MD: -1.94 mmHg; 95% CI: -2.95 to -0.93; I(2) = 8%; p = 0.0002). Similar results were also observed for total cholesterol (MD: -0.13 mmol/l; 95% CI: -0.2 to -0.07; I(2) = 8%; p < 0.0001) and LDL cholesterol (MD: -0.19 mmol/l; 95% CI: -0.3 to -0.09; I(2) = 70%; p = 0.0004). Adverse events included rash, elevated blood pressure, and abdominal discomfort.

CONCLUSION

Green tea intake results in significant reductions in systolic blood pressure, total cholesterol, and LDL cholesterol. The effect size on systolic blood pressure is small, but the effects on total and LDL cholesterol appear moderate. Longer-term independent clinical trials evaluating the effects of green tea are warranted.

Oxidative stress, protein glycation and nutrition--interactions relevant to health and disease throughout the lifecycle

Protein glycation has been studied for over a century now and plays an important role in disease pathogenesis throughout the lifecycle. Strongly related to diabetic complications, glycation of Hb has become the gold standard method for diabetes diagnosis and monitoring. It is however attracting attention in normoglycaemia as well lately. Longitudinal studies increasingly suggest a positive relationship between glycation and the risk of chronic diseases in normoglycaemic individuals, but the mechanisms behind this association remain unclear. The interaction between glycation and oxidative stress may be particularly relevant in the normoglycaemic context, as suggested by recent epidemiological and in vitro evidence. In that context nutritional and lifestyle factors with an influence on redox status, such as smoking, fruit and vegetable and antioxidants consumption, may have the capacity to promote or inhibit glycation. However, experimental data from controlled trials are lacking the quality and rigour needed to reach firm conclusions. In the present review, we discuss the importance of glycation for health through the lifecycle and focus on the importance of oxidative stress as a driver for glycation. The importance of nutrition to modulate glycation is discussed, based on the evidence available and recommendations towards higher quality future research are made.

Linking lifestyle factors and insulin resistance, based on fasting plasma insulin and HOMA-IR in middle-aged Japanese men: a cross-sectional study

OBJECTIVE

Insulin resistance (IR) is regarded as one of the earliest features of many metabolic diseases, and major efforts are aimed at improving insulin function to confront this issue. The aim of this study was to investigate the relationship of body mass index (BMI), cigarette smoking, alcohol intake, physical activity, green tea and coffee consumption to IR.

METHODS

We performed a cross-sectional study of 1542 male self defense officials. IR was defined as the highest quartile of the fasting plasma insulin (≥ 50 pmol/L) or the homeostasis model assessment-estimated IR (HOMA-IR ≥ 1.81). An unconditional logistic model was used to estimate the odds ratio (OR) and 95% confidence interval (CI) for the association between IR and influential factors. Stratified analysis by obesity status (BMI < 25 kg/m(2), non-obese; ≥ 25 kg/m(2), obese) was performed.

RESULTS

IR was significantly positively related to BMI and glucose tolerance, negatively related to alcohol use. Independent of obesity status, significant trends were observed between IR and alcohol use. Drinking 30 mL or more of ethanol per day reduced IR by less than 40%. Strong physical activity was associated with decreased risk of IR based on fasting plasma insulin only in the obese. Coffee consumption was inversely associated with the risk of IR based on HOMA-IR in the non-obese group.

CONCLUSION

Higher coffee consumption may be protective against IR among only the non-obese. Further studies are warranted to examine the effect modification of the obesity status on the coffee-IR association.

Effects of dietary supplementation with epigallocatechin-3-gallate on weight loss, energy homeostasis, cardiometabolic risk factors and liver function in obese women: randomised, double-blind, placebo-controlled clinical trial

The aim of the present study was to examine the effects of green tea epigallocatechin-3-gallate (EGCG) on changes in body composition, energy and substrate metabolism, cardiometabolic risk factors and liver function enzymes after an energy-restricted diet intervention in obese women. In the present randomised, double-blind, placebo-controlled study, eighty-three obese (30 kg/m² > BMI < 40 kg/m²) pre-menopausal women consumed 300 mg/d of EGCG or placebo (lactose). We measured body weight and adiposity (dual-energy X-ray absorptiometry), energy expenditure and fat oxidation rates (indirect calorimetry), blood lipid levels (TAG, total cholesterol, LDL-cholesterol and HDL-cholesterol), insulin resistance, C-reactive protein and liver function markers (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, γ-glutamyltransferase, urea, bilirubin and 2-keto[1-¹³C]isocaproate oxidation) before and after the intervention in the EGCG and control groups. We did not find any significant difference in the changes in body weight (-0.3 kg, 95% CI -5.0, 4.3), fat mass (-0.7 kg, 95% CI -3.5, 2.1), energy (0.3 kJ/kg per d, 95% CI -3.1, 2.7) and fat (-0.1 g/min, 95% CI -0.03, 0.01) metabolism, homeostasis assessment model for insulin resistance (0.2, 95% CI -0.2, 0.7), total cholesterol (-0.21 mmol/l, 95% CI -0.55, 0.13), LDL-cholesterol (-0.15 mmol/l, 95% CI -0.50, 0.20), TAG (-0.4 mmol/l, 95% CI -0.56, 0.29) and liver function markers between the EGCG and control groups. In conclusion, the present results suggest that dietary supplementation with 300 mg/d of EGCG for 12 weeks did not enhance energy-restricted diet-induced adiposity reductions, and did not improve weight-loss-induced changes in cardiometabolic risk factors in obese Caucasian women. The intake of 300 mg/d of EGCG for 12 weeks did not cause any adverse effect on liver function biomarkers.

Catechin- and caffeine-rich teas for control of body weight in humans

Maintaining the level of daily energy expenditure during weight loss and weight maintenance is as important as maintaining satiety while decreasing energy intake. In this context, different catechin- and caffeine-rich teas (CCRTs), such as green, oolong, and white teas, as well as caffeine have been proposed as tools for maintaining or enhancing energy expenditure and for increasing fat oxidation. Tea polyphenols have been proposed to counteract the decrease in metabolic rate that is usually present during weight loss. Their effects may be of particular importance during weight maintenance after weight loss. Although the thermogenic effect of CCRT has the potential to produce significant effects on these metabolic targets as well as on fat absorption and energy intake, possibly via its impact on the gut microbiota and gene expression, a clinically meaningful outcome also depends on compliance by the subjects. Limitations to this approach require further examination, including moderating factors such as genetic predisposition, habitual caffeine intake, and catechin composition and dose. Nevertheless, CCRTs may be useful agents that could help in preventing a positive energy balance and obesity.

Epigallocatechin-3-gallate suppresses transforming growth factor-beta signaling by interacting with the transforming growth factor-beta type II receptor

AIM: To investigate the (-)-epigallocatechin-3-gallate (EGCG) binding to transforming growth factor-β (TGF-β) type II receptor (TGFRII).

METHODS: The expression of α-smooth muscle actin (α-SMA) was used as a marker for fibrotic change in human lung fibroblast MRC-5 cells. The α-SMA expression level was determined by western blotting and immunohistological analysis. We examined whether the anti-fibrotic effects of EGCG on MRC-5 cells was dependent on antioxidant mechanism by using edaravone and N-acetylcysteine (NAC). The suppression effects of EGCG on Smad2/3 activation were studied by confocal fluorescence microscopy. The binding of EGCG to recombinant TGFRII protein was analyzed by immunoprecipitation and affinity chromatography.

RESULTS: When MRC-5 cells were treated with TGF-β, EGCG decreased the expression of α-SMA in a dose dependent manner, whereas catechin did not influence the α-SMA expression in the cells. Except for EGCG, antioxidant compounds (e.g., edaravone and NAC) had no effects on the TGF-β-induced α-SMA expression. Nuclear localization of phosphorylated Smad2/3 was observed after TGF-β treatment; however, EGCG treatment attenuated the nuclear transportation of Smad2/3 in the presence or absence of TGF-β. After a TGFRII expression vector was introduced into COS-7 cells, cell lysates were untreated or treated with EGCG or catechin. The immunoprecipitation experiments using the lysates showed that EGCG dose-dependently bound to TGFRIIand that catechin did not at all. Affinity chromatography study indicated that EGCG would bind to TGFRII.

CONCLUSION: Our results demonstrate that EGCG interacts with TGFRII and inhibits the expression of α-SMA via the TGF-β-Smad2/3 pathway in human lung fibroblast MRC-5 cells.

Effects of green tea or green tea extract on insulin sensitivity and glycaemic control in populations at risk of type 2 diabetes mellitus: a systematic review and meta-analysis of randomised controlled trials

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 populations at risk of type 2 diabetes mellitus (T2DM).

METHODS

Electronic databases, including PUBMED, The Cochrane Library, EMBASE, ISI Web of Knowledge, Chinese Biomedical Literature Database and Chinese Scientific Journals Fulltext Database, were systematically searched to identify randomised controlled trials (RCTs) up to December 2011, supplemented by the Clinicaltrials.gov websites and the reference lists of identified studies. Two reviewers independently selected trials, extracted data, and evaluated the methodological qualities and evidence levels.

RESULTS

Seven RCTs involving 510 participants were identified. There was no statistically significant difference between green tea or green tea extract group and placebo group with regard to fasting plasma glucose [standardised mean difference (SMD) 0.04; 95% confidence interval (CI) -0.15 to 0.24], fasting serum insulin (SMD -0.09; 95% CI -0.30 to 0.11), 2-h plasma glucose in the oral glucose tolerance test (OGTT-2 h) (SMD -0.14; 95% CI -0.63 to 0.34), haemoglobin A₁c (SMD 0.10; 95% CI -0.13 to 0.33) and homeostasis model of insulin resistance (HOMA(IR)) index (SMD -0.06; 95% CI -0.35 to 0.23) in participants at risk of T2DM.

CONCLUSIONS

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 populations at risk of T2DM. Larger, longer-term and high-quality RCTs are needed to further definitely determine the effect of green tea or green tea extract on insulin sensitivity and glycaemic control in populations at risk of T2DM.

Green tea polyphenol epigallocatechin-3-gallate enhance glycogen synthesis and inhibit lipogenesis in hepatocytes

The beneficial effects of green tea polyphenols (GTP) against metabolic syndrome and type 2 diabetes by suppressing appetite and nutrient absorption have been well reported. However the direct effects and mechanisms of GTP on glucose and lipid metabolism remain to be elucidated. Since the liver is an important organ involved in glucose and lipid metabolism, we examined the effects and mechanisms of GTP on glycogen synthesis and lipogenesis in HepG2 cells. Concentrations of GTP containing 68% naturally occurring (−)-epigallocatechin-3-gallate (EGCG) were incubated in HepG2 cells with high glucose (30 mM) under 100 nM of insulin stimulation for 24 h. GTP enhanced glycogen synthesis in a dose-dependent manner. 10 μM of EGCG significantly increased glycogen synthesis by 2fold (P < 0.05) compared with insulin alone. Western blotting revealed that phosphorylation of Ser9 glycogen synthase kinase 3β and Ser641 glycogen synthase was significantly increased in GTP-treated HepG2 cells compared with nontreated cells. 10 μM of EGCG also significantly inhibited lipogenesis (P < 0.01). We further demonstrated that this mechanism involves enhanced expression of phosphorylated AMP-activated protein kinase α and acetyl-CoA carboxylase in HepG2 cells. Our results showed that GTP is capable of enhancing insulin-mediated glucose and lipid metabolism by regulating enzymes involved in glycogen synthesis and lipogenesis.

Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trials

BACKGROUND

The results of studies investigating the effect of green tea on glucose control and insulin sensitivity in humans are inconsistent.

OBJECTIVE

We aimed to quantitatively evaluate the effect of green tea on glucose control and insulin sensitivity.

DESIGN

We performed a strategic literature search of PubMed, EMBASE, and the Cochrane Library (updated to January 2013) for randomized controlled trials that evaluated the effects of green tea and green tea extract on glucose control and insulin sensitivity. Study quality was assessed by using the Jadad scale. Weighted mean differences were calculated for net changes in glycemic measures by using fixed-effects or random-effects models. We conducted prespecified subgroup and sensitivity analyses to explore potential heterogeneity. Meta-regression analyses were conducted to investigate dose effects of green tea on fasting glucose and insulin concentrations.

RESULTS

Seventeen trials comprising a total of 1133 subjects were included in the current meta-analysis. Green tea consumption significantly reduced the fasting glucose and hemoglobin A1c (Hb A1c) concentrations by -0.09 mmol/L (95% CI: -0.15, -0.03 mmol/L; P < 0.01) and -0.30% (95% CI: -0.37, -0.22%; P < 0.01), respectively. Further stratified analyses from high Jadad score studies showed that green tea significantly reduced fasting insulin concentrations (-1.16 μIU/mL; 95% CI: -1.91, -0.40 μIU/mL; P = 0.03).

CONCLUSIONS

This meta-analysis suggested that green tea had favorable effects, ie, decreased fasting glucose and Hb A1c concentrations. Subgroup analyses showed a significant reduction in fasting insulin concentrations in trials with high Jadad scores.

Tissue-specific, development-dependent phenolic compounds accumulation profile and gene expression pattern in tea plant [Camellia sinensis]

Phenolic compounds in tea plant [Camellia sinensis (L.)] play a crucial role in dominating tea flavor and possess a number of key pharmacological benefits on human health. The present research aimed to study the profile of tissue-specific, development-dependent accumulation pattern of phenolic compounds in tea plant. A total of 50 phenolic compounds were identified qualitatively using liquid chromatography in tandem mass spectrometry technology. Of which 29 phenolic compounds were quantified based on their fragmentation behaviors. Most of the phenolic compounds were higher in the younger leaves than that in the stem and root, whereas the total amount of proanthocyanidins were unexpectedly higher in the root. The expression patterns of 63 structural and regulator genes involved in the shikimic acid, phenylpropanoid, and flavonoid pathways were analyzed by quantitative real-time polymerase chain reaction and cluster analysis. Based on the similarity of their expression patterns, the genes were classified into two main groups: C1 and C2; and the genes in group C1 had high relative expression level in the root or low in the bud and leaves. The expression patterns of genes in C2-2-1 and C2-2-2-1 groups were probably responsible for the development-dependent accumulation of phenolic compounds in the leaves. Enzymatic analysis suggested that the accumulation of catechins was influenced simultaneously by catabolism and anabolism. Further research is recommended to know the expression patterns of various genes and the reason for the variation in contents of different compounds in different growth stages and also in different organs.

Effects of green tea catechins with or without caffeine on glycemic control in adults: a meta-analysis of randomized controlled trials

BACKGROUND

The effect of green tea catechins (GTCs) with or without caffeine on glycemic control is controversial.

OBJECTIVE

We aimed to identify and quantify the effects of GTCs or GTC-caffeine mixtures on glucose metabolism in adults.

DESIGN

A comprehensive literature search was conducted to identify relevant trials of GTCs with or without caffeine on markers of glycemic control [fasting blood glucose (FBG), fasting blood insulin (FBI), glycated hemoglobin (Hb A1c), and homeostatic model assessment of insulin resistance (HOMA-IR)]. Weighted mean differences were calculated for net changes by using fixed-effects models. Prespecified subgroup analyses were performed to explore the influence of covariates on net changes in FBG and FBI concentrations.

RESULTS

Twenty-two eligible randomized controlled trials with 1584 subjects were identified. Pooled analyses showed that FBG (-1.48 mg/dL; 95% CI: -2.57, -0.40 mg/dL) decreased significantly with GTCs with or without caffeine, whereas FBI (0.04 μU/mL; 95% CI: -0.36, 0.45 μU/mL), Hb A1c (-0.04%; 95% CI: -0.15, 0.08%), and HOMA-IR (-0.05; 95% CI: -0.37, 0.26) did not. Subgroup analyses indicated that the glucose-lowering effect was apparent when the duration of follow-up was over a median of 12 wk. Overall, no significant heterogeneity was detected for FBG, FBI, Hb A1c, or HOMA-IR.

CONCLUSIONS

The meta-analysis showed that the administration of GTCs with or without caffeine resulted in a significant reduction in FBG. The limited data available on GTCs did not support a positive effect on FBI, Hb A1c, or HOMA-IR. Thus, more large and well-designed trials are needed in the future. This trial was registered at http://www.crd.york.ac.uk/prospero as CRD42012002139.

Food-based ingredients to modulate blood glucose

Maintenance of normal blood glucose levels is important for avoiding chronic diseases such as type 2 diabetes, cardiovascular problems, and obesity. Type 2 diabetes is one of the major health problems affecting the world population and this condition can be exacerbated by poor diet, low physical activity, and genetic abnormalities. Food plays an important role in the management of blood glucose and associated complications in diabetes. This is attributed to the ability of food-based ingredients to modulate blood glucose without causing any adverse health consequences. This chapter focuses on four important food groups such as cereals, legumes, fruits, and spices that have active ingredients such as soluble dietary fiber, polyphenols, and antinutrients with the ability to reduce glycemic and insulin response in humans. Other food ingredients such as simple sugars, sugar alcohols, and some proteins are also discussed in moderation.

Tea consumption and risk of stroke: a dose-response meta-analysis of prospective studies

OBJECTIVE

To determine the association between tea consumption and the risk of stroke.

METHODS

We searched the PubMed database from January 1966 to March 2012 and reviewed reference lists of retrieved articles to identify relevant studies. Studies were included if they reported relative risks (RRs) and corresponding 95% confidence intervals (CIs) of stroke with respect to three or more categories of tea consumption. A random-effects model was used to combine the study-specific risk estimates.

RESULTS

Fourteen studies, consisting of 513,804 participants with a median follow-up of 11.5 years, were included in this meta-analysis. We observed a modest but statistically significant inverse association between tea consumption and risk of stroke. An increase of three cups/d in tea consumption was associated with a 13% decreased risk of stroke (RR 0.87; 95% CI, 0.81-0.94). The decreased risk of stroke with tea consumption was consistent among most subgroups. Based on the three studies that provided results for stroke subtypes, tea consumption was also inversely associated with the risk of ischemic stroke (RR 0.76; 95% CI, 0.69-0.84), but not cerebral hemorrhage (RR 0.96; 95% CI, 0.82-1.11) or subarachnoid hemorrhage (RR 0.81; 95% CI, 0.57-1.16).

CONCLUSIONS

Tea consumption is associated with a decreased risk of stroke, particularly ischemic stroke. More well-designed, rigorously conducted studies are needed in order to make confident conclusions about the association between tea consumption and stroke subtypes.

Green tea for weight loss and weight maintenance in overweight or obese adults

BACKGROUND

Preparations of green tea are used as aids in weight loss and weight maintenance. Catechins and caffeine, both contained in green tea, are each believed to have a role in increasing energy metabolism, which may lead to weight loss. A number of randomised controlled trials (RCTs) evaluating the role of green tea in weight loss have been published; however, the efficacy of green tea preparations in weight loss remains unclear.

OBJECTIVES

To assess the efficacy and safety of green tea preparations for weight loss and weight maintenance in overweight or obese adults.

SEARCH METHODS

We searched the following databases from inception to specified date as well as reference lists of relevant articles: The Cochrane Library (Issue 12, 2011), MEDLINE (December 2011), EMBASE (December 2011), CINAHL (January 2012), AMED (January 2012), Biological Abstracts (January 2012), IBIDS (August 2010), Obesity+ (January 2012), IPA (January 2012) and Web of Science (December 2011). Current Controlled Trials with links to other databases of ongoing trials was also searched.

SELECTION CRITERIA

RCTs of at least 12 weeks' duration comparing green tea preparations to a control in overweight or obese adults.

DATA COLLECTION AND ANALYSIS

Three authors independently extracted data, assessed studies for risk of bias and quality, with differences resolved by consensus. Heterogeneity of included studies was assessed visually using forest plots and quantified using the I(2) statistic. We synthesised data using meta-analysis and descriptive analysis as appropriate; subgroup and sensitivity analyses were conducted. Adverse effects reported in studies were recorded.

MAIN RESULTS

Due to the level of heterogeneity among studies, studies were divided into two groups; those conducted in Japan and those conducted outside Japan. Study length ranged between 12 and 13 weeks. Meta-analysis of six studies conducted outside Japan showed a mean difference (MD) in weight loss of -0.04 kg (95% CI -0.5 to 0.4; P = 0.88; I(2) = 18%; 532 participants). The eight studies conducted in Japan were not similar enough to allow pooling of results and MD in weight loss ranged from -0.2 kg to -3.5 kg (1030 participants) in favour of green tea preparations. Meta-analysis of studies measuring change in body mass index (BMI) conducted outside Japan showed a MD in BMI of -0.2 kg/m(2) (95% CI -0.5 to 0.1; P = 0.21; I(2) = 38%; 222 participants). Differences among the eight studies conducted in Japan did not allow pooling of results and showed a reduction in BMI ranging from no effect to -1.3 kg/m(2) (1030 participants), in favour of green tea preparations over control. Meta-analysis of five studies conducted outside Japan and measuring waist circumference reported a MD of -0.2 cm (95% CI -1.4 to 0.9; P = 0.70; I(2) = 58%; 404 participants). Differences among the eight studies conducted in Japan did not allow pooling of results and showed effects on waist circumference ranging from a gain of 1 cm to a loss of 3.3 cm (1030 participants). Meta-analysis for three weight loss studies, conducted outside Japan, with waist-to-hip ratio data (144 participants) yielded no significant change (MD 0; 95% CI -0.02 to 0.01). Analysis of two studies conducted to determine if green tea could help to maintain weight after a period of weight loss (184 participants) showed a change in weight loss of 0.6 to -1.6 kg, a change in BMI from 0.2 to -0.5 kg/m(2) and a change in waist circumference from 0.3 to -1.7 cm. In the eight studies that recorded adverse events, four reported adverse events that were mild to moderate, with the exception of two (green tea preparations group) that required hospitalisation (reported as not associated with the intervention). Nine studies reported on compliance/adherence, one study assessed attitude towards eating as part of the health-related quality of life outcome. No studies reported on patient satisfaction, morbidity or cost.

AUTHORS' CONCLUSIONS

Green tea preparations appear to induce a small, statistically non-significant weight loss in overweight or obese adults. Because the amount of weight loss is small, it is not likely to be clinically important. Green tea had no significant effect on the maintenance of weight loss. Of those studies recording information on adverse events, only two identified an adverse event requiring hospitalisation. The remaining adverse events were judged to be mild to moderate.

Effect of cocoa and green tea on biomarkers of glucose regulation, oxidative stress, inflammation and hemostasis in obese adults at risk for insulin resistance

BACKGROUND/OBJECTIVES

Flavanols may provide protection against insulin resistance, but little is known about the amounts and types of flavanols that may be efficacious.

SUBJECTS/METHODS

This study was designed to determine whether cocoa flavanols, over a range of intakes, improve biomarkers of glucose regulation, inflammation and hemostasis in obese adults at risk for insulin resistance. As an adjunct, green tea and cocoa flavanols were compared for their ability to modulate these biomarkers. In a randomized crossover design, 20 adults consumed a controlled diet for 5 days along with four cocoa beverages containing 30-900 mg flavanol per day, or tea matched to a cocoa beverage for monomeric flavanol content.

RESULTS

Cocoa beverages produced no significant changes in glucose, insulin, total area under the concentration-time curve (AUC) for glucose or total insulin AUC. As the dose of cocoa flavanols increased, total 8-isoprostane concentrations were lowered (linear contrast, P=0.02), as were C-reactive protein (CRP) concentrations (linear contrast, P=0.01). The relationship between cocoa flavanol levels and interleukin-6 (IL-6) concentrations was quadratic, suggesting that a maximum effective dose was achieved (quadratic contrast, P=0.01). There were no significant effects on measured indices of glucose regulation, nor on those of total 8-isoprostane, CRP and IL-6 concentrations, when cocoa and green tea were compared. However, relative to cocoa, green tea lowered fibrinogen concentrations (P=0.0003).

CONCLUSIONS

Short-term intake of cocoa and green tea flavanols does not appear to improve glucose metabolism; they do affect selected markers of one or more measures of oxidative stress, inflammation or hemostasis in obese adults at risk for insulin resistance.

Phytochemicals and their impact on adipose tissue inflammation and diabetes

Type 2 diabetes mellitus is an inflammatory disease and the mechanisms that underlie this disease, although still incompletely understood, take place in the adipose tissue of obese subjects. Concurrently, the prevalence of obesity caused by Western diet's excessive energy intake and the lack of exercise escalates, and is believed to be causative for the chronic inflammatory state in adipose tissue. Overnutrition itself as an overload of energy may induce the adipocytes to secrete chemokines activating and attracting immune cells to adipose tissue. But also inflammation-mediating food ingredients like saturated fatty acids are believed to directly initiate the inflammatory cascade. In addition, hypoxia in adipose tissue as a direct consequence of obesity, and its effect on gene expression in adipocytes and surrounding cells in fat tissue of obese subjects appears to play a central role in this inflammatory response too. In contrast, revisiting diet all over the world, there are also some natural food products and beverages which are associated with curative effects on human health. Several natural compounds known as spices such as curcumin, capsaicin, and gingerol, or secondary plant metabolites catechin, resveratrol, genistein, and quercetin have been reported to provide an improved health status to their consumers, especially with regard to diabetes, and therefore have been investigated for their anti-inflammatory effect. In this review, we will give an overview about these phytochemicals and their role to interfere with inflammatory cascades in adipose tissue and their potential for fighting against inflammatory diseases like diabetes as investigated in vivo.

A review of the hypoglycemic effects of five commonly used herbal food supplements

Hyperglycemia is a pathological condition associated with prediabetes and diabetes. The incidence of prediabetes and diabetes is increasing and imposes great burden on healthcare worldwide. Patients with prediabetes and diabetes have significantly increased risk for cardiovascular diseases and other complications. Currently, management of hyperglycemia includes pharmacological interventions, physical exercise, and change of life style and diet. Food supplements have increasingly become attractive alternatives to prevent or treat hyperglycemia, especially for subjects with mild hyperglycemia. This review summarized current patents and patent applications with relevant literature on five commonly used food supplements with claims of hypoglycemic effects, including emblica officinalis (gooseberry), fenugreek, green tea, momordica charantia (bitter melon) and cinnamon. The data from human clinical studies did not support a recommendation for all five supplements to manage hyperglycemia. Fenugreek and composite supplements containing emblica officinalis showed the most consistency in lowering fasting blood sugar (FBS) or glycated hemoglobin (HbA1c) levels in diabetic patients. The hypoglycemic effects of cinnamon and momordica charantia were demonstrated in most of the trials with some exceptions. However, green tea exhibited limited benefits in reducing FBS or HbA1c levels and should not be recommended for managing hyperglycemia. Certain limitations are noticed in a considerable number of clinical studies including small sample size, poor experimental design and considerable variations in participant population, preparation format, daily dose, and treatment duration. Future studies with more defined participants, standardized preparation and dose, and improved trial design and size are warranted.

Tea consumption and incidence of type 2 diabetes in Europe: the EPIC-InterAct case-cohort study

Background

In previous meta-analyses, tea consumption has been associated with lower incidence of type 2 diabetes. It is unclear, however, if tea is associated inversely over the entire range of intake. Therefore, we investigated the association between tea consumption and incidence of type 2 diabetes in a European population.

Methodology/Principal Findings

The EPIC-InterAct case-cohort study was conducted in 26 centers in 8 European countries and consists of a total of 12,403 incident type 2 diabetes cases and a stratified subcohort of 16,835 individuals from a total cohort of 340,234 participants with 3.99 million person-years of follow-up. Country-specific Hazard Ratios (HR) for incidence of type 2 diabetes were obtained after adjustment for lifestyle and dietary factors using a Cox regression adapted for a case-cohort design. Subsequently, country-specific HR were combined using a random effects meta-analysis. Tea consumption was studied as categorical variable (0, >0-<1, 1-<4, ≥4 cups/day). The dose-response of the association was further explored by restricted cubic spline regression. Country specific medians of tea consumption ranged from 0 cups/day in Spain to 4 cups/day in United Kingdom. Tea consumption was associated inversely with incidence of type 2 diabetes; the HR was 0.84 [95%CI 0.71, 1.00] when participants who drank ≥4 cups of tea per day were compared with non-drinkers (p_{linear trend} = 0.04). Incidence of type 2 diabetes already tended to be lower with tea consumption of 1-<4 cups/day (HR = 0.93 [95%CI 0.81, 1.05]). Spline regression did not suggest a non-linear association (p_{non-linearity} = 0.20).

Conclusions/Significance

A linear inverse association was observed between tea consumption and incidence of type 2 diabetes. People who drink at least 4 cups of tea per day may have a 16% lower risk of developing type 2 diabetes than non-tea drinkers.

Green tea catechins decrease total and low-density lipoprotein cholesterol: a systematic review and meta-analysis

Green tea catechins (GTCs) have been studied in randomized control trials for their lipid-lowering effects. Studies, however, have been small and demonstrated conflicting results. The objective of this study was to perform a systematic review and meta-analysis of randomized controlled trials evaluating the relationship between GTCs and serum lipid levels, including total, low-density lipoprotein (LDL), high-density lipoprotein (HDL) cholesterol, and triglycerides. A systematic literature search of MEDLINE, EMBASE, Cochrane CENTRAL, and the Natural Medicines Comprehensive Database was conducted through March 2010. Randomized controlled trials evaluating GTCs vs control in human beings and reporting efficacy data on at least one of the aforementioned serum lipid endpoints were included. Weighted mean differences for changes from baseline (with 95% confidence intervals [CIs]) for lipid endpoints were calculated using random-effects models. Twenty trials (N=1,415) met all inclusion criteria. Upon meta-analysis, GTCs at doses ranging from 145 to 3,000 mg/day taken for 3 to 24 weeks reduced total (-5.46 mg/dL [-0.14 mmol/L]; 95% CI -9.59 to -1.32) and LDL cholesterol (-5.30 mg/dL [-0.14 mmol/L]; 95% CI -9.99 to -0.62) compared to control. GTCs did not significantly alter HDL cholesterol (-0.27 mg/dL [-0.007 mmol/L]; 95% CI -1.62 to 1.09) or triglyceride (3.00 mg/dL [-0.034 mmol/L]; 95% CI -2.73 to 8.73) levels. The consumption of GTCs is associated with a statistically significant reduction in total and LDL cholesterol levels; however, there was no significant effect on HDL cholesterol or triglyceride levels.

Health effects of green tea catechins in overweight and obese men: a randomised controlled cross-over trial

Regular consumption of green tea may be cardioprotective. In the present study we investigated the health effects of dietary supplementation with green tea catechins and the potential modifying effect of the catechol-O-methyltransferase (COMT) Val/Met genotype. Subjects (sedentary males, aged 40-69 years, with BMI ≥ 28 and ≤ 38 kg/m(2)) were randomly assigned to consume decaffeinated green tea extract (DGT; 530 mg containing about 400 mg total catechins/capsule, twice daily) and placebo in a complete cross-over design. Ambulatory blood pressure and biomarkers of metabolic function (cholesterol, TAG, glucose and insulin) were measured at weeks 0 and 6. Although a marked increase in the concentration of plasma epigallocatechin gallate (EGCG), urinary epigallocatechin (EGC) and urinary 4'-O-methyl EGC was found after DGT treatment, no effect on blood pressure or biomarkers of metabolic function was observed. However, a period × treatment interaction (P < 0·05) was detected for body-weight change. Despite a similar increase in estimated energy intake during intervention period 1, body weight decreased by 0·64 (sd 2·2) kg and increased by 0·53 (sd 1·9) kg in the DGT and placebo groups, respectively (P = 0·025), suggesting a protective effect of green tea catechins on weight gain. Additionally, the COMT Val/Met genotype influenced urinary accumulation of EGC and 4'-O-methyl EGC (P < 0·01). Mean concentrations were lower in individuals homozygous for the high-activity G-allele, possibly reflecting increased metabolic flux and a more rapid conversion to downstream metabolic species, compared with individuals carrying at least one copy of the low-activity A-allele. Additional studies are needed to confirm these findings and further explore the modifying effect of genotype.

Protocol for minimizing the risk of metachronous adenomas of the colorectum with green tea extract (MIRACLE): a randomised controlled trial of green tea extract versus placebo for nutriprevention of metachronous colon adenomas in the elderly population

Background

Prevention of colorectal cancer is a major health care issue. People who have undergone colonoscopy screening and had colorectal polyps removed have a higher risk of being diagnosed with polyps again compared to the normal population. Therefore, it would be ideal to find appropriate means that effectively help to prevent the reoccurrence of polyps after polypectomy. So far, pharmaceutical chemoprevention with NSAIDs including aspirin has been shown to be effective but not gained general acceptance due to side effects. Nutraceuticals such as polyphenols from tea plants have demonstrated remarkable therapeutic and preventive effects in molecular, epidemiological and clinical trials. However, placebo-controlled trials demonstrating the efficacy of nutraceuticals for the (secondary) prevention of colorectal polyps as precursors for colorectal cancer are missing.

Methods/Design

We present the design of a randomized, placebo controlled, multicentre trial to investigate the effect of diet supplementation with green tea extract containing 300 mg epigallocatechin gallate (EGCG), the major polyphenol in green tea, on the recurrence of colon adenomas. Patients who have undergone polypectomy for colonic polyps will be randomized to receive either green tea extract containing 150 mg EGCG two times daily or a placebo over the course of three years. After a one month run-in period in which all patients will receive the active intervention, 2534 patients will be randomized, and 2028 patients are expected to complete the whole study course. Incidence, number and histology of adenoma at endpoint colonoscopy at three years will be compared in both groups.

Discussion

The beneficial safety profile of decaffeinated green tea extract, the quantifiable and known active content EGCG, and the accumulating evidence of its cancer preventive potential require, in our view, a validation of this compound for the nutriprevention of colorectal adenoma. Good accessibility and low costs might render this neutraceutical a top candidate for wider use as food supplement in colon cancer prevention.

Trial registration

ClinicalTrials.gov: NCT01360320

Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials

BACKGROUND

The effect of green tea beverage and green tea extract on lipid changes is controversial.

OBJECTIVE

We aimed to identify and quantify the effect of green tea and its extract on total cholesterol (TC), LDL cholesterol, and HDL cholesterol.

DESIGN

We performed a comprehensive literature search to identify relevant trials of green tea beverages and extracts on lipid profiles in adults. Weighted mean differences were calculated for net changes in lipid concentrations by using fixed-effects or random-effects models. Study quality was assessed by using the Jadad score, and a meta-analysis was conducted.

RESULTS

Fourteen eligible randomized controlled trials with 1136 subjects were enrolled in our current meta-analysis. Green tea consumption significantly lowered the TC concentration by 7.20 mg/dL (95% CI: -8.19, -6.21 mg/dL; P < 0.001) and significantly lowered the LDL-cholesterol concentration by 2.19 mg/dL (95% CI: -3.16, -1.21 mg/dL; P < 0.001). The mean change in blood HDL-cholesterol concentration was not significant. Subgroup and sensitivity analyses showed that these changes were not influenced by the type of intervention, treatment dose of green tea catechins, study duration, individual health status, or quality of the study. Overall, no significant heterogeneity was detected for TC, LDL cholesterol, and HDL cholesterol; and results were reported on the basis of fixed-effects models.

CONCLUSION

The analysis of eligible studies showed that the administration of green tea beverages or extracts resulted in significant reductions in serum TC and LDL-cholesterol concentrations, but no effect on HDL cholesterol was observed.

Effect of green tea catechins on the postprandial glycemic response to starches differing in amylose content

The effect of tea polyphenols (TPLs), specifically tea catechins, on the postprandial glycemic response to cooked starches differing in amylose contents was investigated. The in vivo test using a mouse model showed a moderate reduction of the postprandial glycemic response to co-cooked normal (containing 27.8% amylose) or waxy corn starch with 10% TPLs (dry weight of starch), while an augmented glycemic response with a delayed blood glucose peak was observed when high amylose corn starch (HAC, containing 79.4% amylose) was used as the starch component. Enzyme kinetics results demonstrated that TPLs noncompetitively inhibit the digestion of waxy or normal corn starch, while the digestion rate of HAC starch was increased in the presence of TPLs, which supports the observed postprandial glycemic responses. Further studies using X-ray powder diffraction showed that the diffraction intensity (area under the diffraction curves) of normal and HAC starch was increased by 45% and 74%, respectively, whereas no change was observed for waxy corn starch. Consistently, dynamic laser light scattering studies using a solution of pure amylose showed an increased hydrodynamic radius of amylose molecules from ∼54 nm to ∼112 nm in the presence of TPLs. These experimental results indicate that there might exist an interaction between TPLs and amylose, which facilitates the association of amylose molecules to form a special nonordered structure that can produce a high and sustained postprandial glycemic response. Thus, a combination of tea polyphenols and specific starches could be used to manipulate postprandial glycemic response for glycemic control and optimal health.

Polyphenols: planting the seeds of treatment for the metabolic syndrome

Greater understanding about the pathogenesis of metabolic syndrome and potential causes suggests that plant polyphenols might be useful as a treatment. Dietary excess energy can be stored in adipocytes, leading to the release of proinflammatory cytokines and adipose-related hormones that cause vascular injury. Plant polyphenols, organic compounds found in numerous plant species and their fruits, are being actively studied as potential treatments for components of the metabolic syndrome. Individual polyphenols that have been examined include resveratrol, quercetin, epigallocathechin-3-gallate, and curcumin. Resveratrol lowers weight, blood pressure, glucose, and insulin resistance in rodents, and a human trial is currently underway. Quercetin decreases lipid and glucose levels in obese rats, and in a human investigation of subjects with the metabolic syndrome has lowered blood pressure without significant alteration of lipids. Epigallocathechin-3-gallate-induced weight loss has attenuated glucose levels and insulin resistance in rodents and improved hemoglobin A(1c) and lipid in human studies. Plant extracts also can be used. Grape seed and chokeberry extracts have decreased blood pressure and lipid levels in small human trials. Other human investigations have shown the beneficial effects of cocoa, coffee, carob, and Momordica charantia. Thus far, most studies have involved a small number of subjects and have been of short duration. Future studies should be designed to account for a disease process in which the pathogenic factors may take place for years before disease manifestations take place, the possibly limited bioavailability of polyphenols, and the potential need to provide combinations or modifications of polyphenols.

The impact of the catechol-O-methyltransferase genotype on the acute responsiveness of vascular reactivity to a green tea extract

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 samples 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.

Does green tea affect postprandial glucose, insulin and satiety in healthy subjects: a randomized controlled trial

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 postprandial 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 randomized to either 300 ml of green tea or water. This was consumed together with a breakfast consisting of white bread and sliced turkey. Blood samples 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 NUMBER

NCT01086189.