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

Effects of green tea supplementation on antioxidant status and inflammatory markers in adults: a grade-assessed systematic review and dose-response meta-analysis of randomised controlled trials

Green tea, a plant rich in bioactive compounds, has been highlighted for its beneficial effects. In the present systematic review and meta-analysis of randomised controlled trials (RCTs), the impact of green tea on inflammatory and oxidative markers is investigated. Using pre-defined keywords, online databases (PubMed, Scopus, Web of Science Core Collection, and Google Scholar) were searched for relevant articles, published from inception up to February 2024. The outcomes included C-reactive protein (CRP), tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1 beta (IL-1β), total antioxidant capacity (TAC), malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GPX). Analyses of subgroups, linear, and non-linear associations were also carried out. Out of 1264 records initially retrieved, 38 RCTs were included. Supplementation with green tea improved the following indicators: IL-1β (weighted mean difference (WMD): -0.10 pg/mL; 95% CI: -0.15, -0.06), MDA (WMD: -0.40 mcmol/L; 95 % CI: -0.63, -0.18), TAC (WMD: 0.09 mmol/L; 95% CI: 0.05, 0.13), SOD (WMD: 17.21 u/L; 95% CI: 3.24, 31.19), and GPX (WMD: 3.90 u/L; 95% CI: 1.85, 5.95); but failed to improve others, including CRP (WMD: 0.01 mg/L; 95% CI: -0.14, 0.15), IL-6 (WMD: -0.34 pg/mL; 95% CI:-0.94, 0.26), and TNF-α (WMD: -0.07 pg/mL; 95% CI: -0.42, 0.28). Supplementation with green tea can improve the body's oxidative status. However, the results showed no significant effect of green tea on inflammatory markers, except for IL-1β. Further studies are needed to determine the effectiveness of green tea, particularly on inflammatory status.

A Narrative Review on Plant Extracts for Metabolic Syndrome: Efficacy, Safety, and Technological Advances

Metabolic syndrome, a global health concern, is characterized by visceral obesity, hyperglycemia, dyslipidemia, hypertension, and chronic low-grade inflammation. Current therapeutic options are limited by their varying efficacy and significantly adverse side effects, fueling interest in natural products, particularly plant extracts, as potential preventive interventions for high-risk individuals. This review examines the role of plant extracts in mitigating metabolic syndrome risk factors, addressing safety concerns and exploring associated technological advancements. The literature indicates that plant extracts hold promise for addressing the pathophysiology of metabolic dysfunction. However, challenges such as safety concerns, a lack of standardized regulation, and potential drug-plant interactions currently limit their clinical application. Rigorous, long-term clinical trials are necessary to confirm the efficacy and safety of plant extracts before they can be established as a preventive strategy for managing metabolic syndrome.

The effect of green tea on patients with type 2 diabetes mellitus: A meta-analysis

BACKGROUND

To systematically evaluate the effect of green tea on patients with type 2 diabetes.

METHODS

A computer search Cochrane, PubMed, Embase, CNKI, Wanfang, VIP, and other Chinese and English databases were conducted for randomized controlled trials of green tea in the treatment of patients with type 2 diabetes. The duration of these trials spanned from the establishment of the database to January 10, 2024. The obtained data were subjected to meta-analysis using Stata15.1 software. A total of 15 articles were included, encompassing 722 patients.

RESULTS

The meta-analysis results showed that compared to the control group, green tea intervention significantly improved the improvement of fasting blood glucose (SMD = -0.41, 95% CI: -0.67 to -0.19, P = .001), glycated hemoglobin (SMD = -0.68, 95% CI: -1.15 to 0.21, P = .004) and insulin resistance index (SMD = -0.70, 95% CI: -1.18 to -0.22, P = .005) in the experimental group compared to the control group. The differences were statistically significant (P < .05).

CONCLUSION

Green tea significantly improves fasting blood glucose, glycated hemoglobin and insulin resistance in patients with type 2 diabetes.

Flavan-3-ols and Vascular Health: Clinical Evidence and Mechanisms of Action

Cardiovascular diseases (CVDs) are one of the main causes of mortality and morbidity worldwide. A healthy diet rich in plant-derived compounds such as (poly)phenols appears to have a key role in improving cardiovascular health. Flavan-3-ols represent a subclass of (poly)phenols of great interest for their possible health benefits. In this review, we summarized the results of clinical studies on vascular outcomes of flavan-3-ol supplementation and we focused on the role of the microbiota in CVD. Clinical trials included in this review showed that supplementation with flavan-3-ols mostly derived from cocoa products significantly reduces blood pressure and improves endothelial function. Studies on catechins from green tea demonstrated better results when involving healthy individuals. From a mechanistic point of view, emerging evidence suggests that microbial metabolites may play a role in the observed effects. Their function extends beyond the previous belief of ROS scavenging activity and encompasses a direct impact on gene expression and protein function. Although flavan-3-ols appear to have effects on cardiovascular health, further studies are needed to clarify and confirm these potential benefits and the rising evidence of the potential involvement of the microbiota.

Quercetin and Catechin Protects Leptin-Deficient Lepob/Ob Mice Against Alloxan-Induced Diabetes and Hepatotoxicity via Suppression of Oxidative Stress and Inflammation

Background

The study focuses on evaluating the combined effects of quercetin (QCT) and catechin (CAT), both plant-based antioxidants, on alloxan-induced liver toxicity and diabetes in leptin-deficient (Lepob/ob) mice. Diabetes is a metabolic disorder characterized by high blood glucose levels due to inadequate insulin secretion or insulin resistance.

Methods

Thirty mice were divided into five groups of 6, including: normal control, diabetic control, diabetic mice treated with 150 mg/kg CAT, diabetic mice treated with 150 mg/kg QCT, and diabetic mice treated with 150 mg/kg CAT, and 150 mg/kg QCT for seven days. Mice were anesthetized after overnight fasting on the 8th day, and the blood sample was collected and the levels of antioxidants and pro-inflammatory factors in serum, and the expression of ADP-ribose polymerase (PARP) protein were measured, and histological studies were performed.

Results

The results showed that diabetic mice receiving QCT and CAT showed lower liver enzymes, fasting blood sugar (FBS), blood urea nitrogen (BUN), creatinine (Cr), cholesterol, triglyceride, low-density lipoprotein (LDL), TNF-α, and thiobarbituric acid reactive substances (TBARS) levels and increased high-density lipoprotein (HDL), total thiol, catalase, superoxide dismutase (SOD), and glutathione peroxidase (GPx) levels in the liver compared to the ALLO group alone (P<0.001). The level of PARP protein significantly declined in the ALLO group compared to the control group.

Conclusions

The findings of this study demonstrated that QCT, and CAT are reasonably effective in preventing hepatotoxicity and diabetes in mice.

Effect of Green Tea Supplementation on Inflammatory Markers among Patients with Metabolic Syndrome and Related Disorders: A Systematic Review and Meta-Analysis

Several randomized controlled trials (RCTs) have investigated the potential benefits of green tea on the inflammatory process in metabolic syndrome (MetS). However, the results are inconclusive and inconsistent. In the present study, we performed a literature review and meta-analysis to evaluate the effect of green tea supplementation on inflammatory markers [e.g., tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), and interleukin-6 (IL-6)] among patients with MetS and related disorders. We systematically searched for relevant publications up to March 2022 in the PubMed, Scopus, Web of Science, and SciELO databases. The review was registered with PROSPERO (CRD42022320345). Mean differences with 95% confidence intervals were pooled on the basis of the random effects model to compare the effects of green tea with placebo. We used meta-regression and subgroup analyses to determine the cause of heterogeneity and performed study quality assessment using the Grading of Recommendations Assessment, Development, and Evaluation method. We assessed publication bias using funnel plots and Egger's tests. Out of the total 15 RCTs that were included in this systematic review, 12 were chosen for the meta-analysis. The results revealed that green tea significantly decreased TNF-α levels but did not affect CRP and IL-6 levels. Subgroup analysis showed that green tea supplementation in studies lasting ≤8 weeks significantly increased CRP levels. Furthermore, meta-regression analysis demonstrated a significant association between increasing IL-6 concentration and treatment duration. According to our meta-analysis, green tea was shown to considerably lower circulating TNF-α levels. To confirm these findings, carefully planned trials are required.

The effects of green tea extract supplementation on body composition, obesity-related hormones and oxidative stress markers: a grade-assessed systematic review and dose-response meta-analysis of randomised controlled trials

Research indicates that green tea extract (GTE) supplementation is beneficial for a range of conditions, including several forms of cancer, CVD and liver diseases; nevertheless, the existing evidence addressing its effects on body composition, oxidative stress and obesity-related hormones is inconclusive. This systematic review and meta-analysis aimed to investigate the effects of GTE supplementation on body composition (body mass (BM), body fat percentage (BFP), fat mass (FM), BMI, waist circumference (WC)), obesity-related hormones (leptin, adiponectin and ghrelin) and oxidative stress (malondialdehyde (MDA) and total antioxidant capacity (TAC)) markers. We searched proper databases, including PubMed/Medline, Scopus and Web of Science, up to July 2022 to recognise published randomised controlled trials (RCT) that investigated the effects of GTE supplementation on the markers mentioned above. A random effects model was used to carry out a meta-analysis. The heterogeneity among the studies was assessed using the I2 index. Among the initial 11 286 studies identified from an electronic database search, fifty-nine studies involving 3802 participants were eligible to be included in this meta-analysis. Pooled effect sizes indicated that BM, BFP, BMI and MDA significantly reduced following GTE supplementation. In addition, GTE supplementation increased adiponectin and TAC, with no effects on FM, leptin and ghrelin. Certainty of evidence across outcomes ranged from low to high. Our results suggest that GTE supplementation can attenuate oxidative stress, BM, BMI and BFP, which are thought to negatively affect human health. Moreover, GTE as a nutraceutical dietary supplement can increase TAC and adiponectin.

The effect of green tea (Camellia sinensis) on lipid profiles and renal function in people with type 2 diabetes and nephropathy: a randomized controlled clinical trial

Introduction

Diabetic nephropathy is one of the most important microvascular complications of diabetes. Despite the modern treatments, herbs or medicinal plants have gained wide attention. One of these herbs is green tea (Camellia sinensis), which may have an impact on renal function, lipid profiles, and HbA1c. However, the evidence for this is unclear and limited. The present study aimed to evaluate the effect of different doses of green tea on these parameters in type 2 diabetes patients (T2DM) with nephropathy.

Methods

Sixty-six individuals with T2DM nephropathy (aged 30-70 years) were randomly assigned to receive three cups of green tea/day (n = 22), two cups of green tea/day (n = 22), and the control group (n = 22) for 12 weeks. Lipid profiles, glycated hemoglobin A1c (HbA1c), and renal markers were measured before and after intervention. Data were analyzed using SPSS software version 23. One-way analysis of variance (ANOVA), least significant difference (LSD) post hoc, and analysis of covariance were used to compare quantitative variables.

Results

In total, 64 participants completed the study. Consuming three cups of infusion green tea per day (7.5 gr) led to a significant reduction in serum levels of total cholesterol (p = 0.009) and HbA1c (p = 0.006) and increased in high-density lipoprotein cholesterol (HDL-C) (p = 0.02) compared with the control group who did not drink green tea. However, no significant differences were observed for other variables.

Conclusion

In general, it was found that drinking three cups of green tea infusion (7.5 gr) per day produced beneficial effects on some lipid profiles and HbA1c without any adverse effects on renal function in patients with T2DM nephropathy. More studies are needed to fully elucidate these findings.

Clinical trial registration

Iranian Registry of Clinical Trials (www.irct.ir) under registry number: IRCT2014020114538N2.

Beverage consumption and mortality among adults with type 2 diabetes: prospective cohort study

OBJECTIVE

To investigate the intake of specific types of beverages in relation to mortality and cardiovascular disease (CVD) outcomes among adults with type 2 diabetes.

DESIGN

Prospective cohort study.

SETTING

Health professionals in the United States.

PARTICIPANTS

15 486 men and women with a diagnosis of type 2 diabetes at baseline and during follow-up (Nurses' Health Study: 1980-2018; and Health Professionals Follow-Up Study: 1986-2018). Beverage consumption was assessed using a validated food frequency questionnaire and updated every two to four years.

MAIN OUTCOME MEASURES

The main outcome was all cause mortality. Secondary outcomes were CVD incidence and mortality.

RESULTS

During an average of 18.5 years of follow-up, 3447 (22.3%) participants with incident CVD and 7638 (49.3%) deaths were documented. After multivariable adjustment, when comparing the categories of lowest intake of beverages with the highest intake, the pooled hazard ratios for all cause mortality were 1.20 (95% confidence interval 1.04 to 1.37) for sugar sweetened beverages (SSBs), 0.96 (0.86 to 1.07) for artificially sweetened beverages (ASBs), 0.98 (0.90 to 1.06) for fruit juice, 0.74 (0.63 to 0.86) for coffee, 0.79 (0.71 to 0.89) for tea, 0.77 (0.70 to 0.85) for plain water, 0.88 (0.80 to 0.96) for low fat milk, and 1.20 (0.99 to 1.44) for full fat milk. Similar associations were observed between the individual beverages and CVD incidence and mortality. In particular, SSB intake was associated with a higher risk of incident CVD (hazard ratio 1.25, 95% confidence interval 1.03 to 1.51) and CVD mortality (1.29, 1.02 to 1.63), whereas significant inverse associations were observed between intake of coffee and low fat milk and CVD incidence. Additionally, compared with those who did not change their consumption of coffee in the period after a diabetes diagnosis, a lower all cause mortality was observed in those who increased their consumption of coffee. A similar pattern of association with all cause mortality was also observed for tea, and low fat milk. Replacing SSBs with ABSs was significantly associated with lower all cause mortality and CVD mortality, and replacing SSBs, ASBs, fruit juice, or full fat milk with coffee, tea, or plain water was consistently associated with lower all cause mortality.

CONCLUSIONS

Individual beverages showed divergent associations with all cause mortality and CVD outcomes among adults with type 2 diabetes. Higher intake of SSBs was associated with higher all cause mortality and CVD incidence and mortality, whereas intakes of coffee, tea, plain water, and low fat milk were inversely associated with all cause mortality. These findings emphasize the potential role of healthy choices of beverages in managing the risk of CVD and premature death overall in adults with type 2 diabetes.

The effects of green tea supplementation on cardiovascular risk factors: A systematic review and meta-analysis

Purpose

A bulk of observational studies have revealed the protective role of green tea supplementation in cardiovascular diseases. The current systematic review and meta-analysis study aimed to establish the effects of green tea supplementation on cardiovascular risk factors including lipid profile, blood pressure, glycemic control markers and CRP.

Methods

A systematic literature search of randomized clinical trials (RCTs) that investigated the effects of green tea supplementation and cardiovascular risk factors was undertaken in online databases including PubMed/Medline, Scopus, Web of Science, and Embase using a combination of green tea and cardiovascular risk factors search terms. Meta-analyses were carried out using a random-effects model. The I2 index was used to assess the heterogeneity of RCTs.

Results

Among the initial 11,286 studies that were identified from electronic databases search, 55 eligible RCTs with 63 effect sizes were eligible. Results from the random effects meta-analysis showed that GTE supplementation significantly reduced TC (WMD = -7.62; 95% CI: -10.51, -4.73; P = < 0.001), LDL-C (WMD = -5.80; 95% CI: -8.30, -3.30; P = < 0.001), FBS (WMD = -1.67; 95% CI: -2.58, -0.75; P = < 0.001), HbA1c (WMD = -0.15; 95% CI: -0.26, -0.04; P = 0.008), DBP (WMD = -0.87; 95% CI: -1.45, -0.29; P = 0.003), while increasing HDL-C (WMD = 1.85; 95% CI: 0.87, 2.84; P = 0.010). Subgroup analyses based on the duration of supplementation (≥ 12 vs. < 12 weeks), dose of green tea extract (GTE) (≥1,000 vs. < 1,000 mg/d), sex (male, female, and both), baseline serum levels of lipid profile, and glycemic control factors demonstrated different results for some risk factors.

Conclusion

The current study suggests improvements in the lipid and glycemic profiles following green tea supplementation. These findings support previous evidence showing the health benefits of green tea supplementation on cardiometabolic risk factors.

Coffee or tea: Anti-inflammatory properties in the context of atherosclerotic cardiovascular disease prevention

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of premature death worldwide. Inflammation and its biomarkers, like C-reactive protein (CRP), among the risk factors, such as hypertension, lipid disorders, and diabetes, may be also responsible for the residual cardiovascular disease (CVD) risk. Modern lipid-lowering treatment with statins, ezetimibe, PCSK9 inhibitors, or bempedoic acid does not fully protect against inflammation. The recommendations of the International Lipid Expert Panel (ILEP) indicate selected nutraceuticals with anti-inflammatory properties. Diet may have a significant impact on inflammation. Especially interesting in the context of inflammation is the consumption of coffee and tea. These drinks in many observational studies significantly reduced cardiovascular risk and mortality. The question is whether the anti-inflammatory effects of these drinks contribute significantly to the observed clinical effects. Thus, in this narrative review, we primarily discuss the anti-inflammatory properties of consuming tea and coffee. Based on a comprehensive analysis of the studies and their meta-analyses, inconsistent results were obtained, which makes it impossible to conclusively state how clinically significant the potential anti-inflammatory properties of black and green tea and coffee are. A number of confounding factors can cause the inconsistency of the available results. Consumption of tea and coffee appears to increase adiponectin concentrations, decrease reactive oxygen species, decrease low density lipoprotein (LDL) cholesterol concentrations (effect of green tea, etc.). Despite the still uncertain anti-inflammatory effect of tea and coffee, we recommend their consumption as a part of the healthy diet.

Effects of green tea polyphenol extract and epigallocatechin-3-O-gallate on diabetes mellitus and diabetic complications: Recent advances

Diabetes mellitus is one of the major non-communicable diseases accounting for millions of death annually and increasing economic burden. Hyperglycemic condition in diabetes creates oxidative stress that plays a pivotal role in developing diabetes complications affecting multiple organs such as the heart, liver, kidney, retina, and brain. Green tea from the plant Camellia sinensis is a common beverage popular in many countries for its health benefits. Green tea extract (GTE) is rich in many biologically active compounds, e.g., epigallocatechin-3-O-gallate (EGCG), which acts as a potent antioxidant. Recently, several lines of evidence have shown the promising results of GTE and EGCG for diabetes management. Here, we have critically reviewed the effects of GTE and EGCC on diabetes in animal models and clinical studies. The concerns and challenges regarding the clinical use of GTE and EGCG against diabetes are also briefly discussed. Numerous beneficial effects of green tea and its catechins, particularly EGCG, make this natural product an attractive pharmacological agent that can be further developed to treat diabetes and its complications.

The effect of Green green tea consumption on body mass index, lipoprotein, liver enzymes, and liver cancer: An updated systemic review incorporating a meta-analysis

INTRODUCTION

Green tea is related to the reduction of liver enzymes, lipoprotein, and body mass index. However, some reports related green tea to the risk of developing liver cancer, but their outcomes were conflicting. Hence, the present study aimed to determine the relationship between green tea intake and lipoprotein, liver enzymes, body mass index, and liver cancer.

METHODS

A systematic literature search up to January 2022 was performed and 22 studies with a total of 169599 subjects participated in the studies with 97316 subjects of them used green tea intake. Odds ratio (OR) or standardized mean difference (MD) with 95% confidence intervals (CIs) was calculated to evaluate the relationship between green tea intake and lipoprotein, liver enzymes, body mass index, and liver cancer using the dichotomous or the contentious method with a random effect model.

RESULTS

Green tea intake significantly lowered the risk of developing liver cancer (OR, 0.85; 95% CI, 0.74 to 0.97, p = 0.02), and body mass index (MD, -0.69; 95% CI, -0.95to -0.42, p < 0.001) compared to no green tea intake. Also, there was a significant lowering effect of green tea intake on liver enzymes including alanine aminotransferase (MD, -0.65; 95% CI, -0.92 to -0.38, p < 0.001), and aspartate aminotransferase (MD, -0.77; 95% CI, -1.40 to -0.14, p = 0.02) compared to no green tea intake. There was also a significant lowering effect of green tea intake on lipoprotein including triglycerides (MD, -0.70; 95% CI, -1.35 to -0.04, p = 0.04), total cholesterol (MD, -0.39; 95% CI, -0.74 to -0.04, p = 0.03) and law-density lipoprotein (MD, -0.44; 95% CI, -0.69- -0.19, p < 0.001) compared to no green tea intake. However, no significant different was found between green tea intake and no green tea intake on high-density lipoprotein (MD, 0.16; 95% CI, -0.11 to 0.44, p = 0.24).

CONCLUSIONS

Based on this meta-analysis, green tea intake had a significant lowering effect on the risk of developing liver cancer and had a significantly improving effect on body mass index, liver enzymes, and lipoprotein compared to no green tea intake. These results suggest that green tea may be added to the daily dietary program to improve cardiovascular status with no possible risk of liver cancer. It even may have a protecting effect against liver cancer in the usual daily number of cups.

Ethyl acetate fraction of Fagara zanthoxyloides root-bark possess antidiabetic property against alloxan-induced diabetes and its complications in Wistar rat model

ETHNOPHARMACOLOGICAL RELEVANCE

Fagara zanthoxyloides Lam., an African traditional medicinal plant, is used for treatment of malaria and diabetes.

AIM

To investigate the antidiabetic property of ethyl acetate fraction of F. zanthoxyloides root-bark (EAFFZRB) on alloxan-induced diabetic rats.

MATERIALS AND METHODS

Extraction, isolation, preliminary phytochemical analysis, and acute toxicity study of ethanol extract and fractions of F. zanthoxyloides root-bark were achieved using standard methods. Phyto-constituents in EAFFZRB were identified using HPLC technique. Forty-eight male Wistar rats (140-185 g) were randomized into 6 groups (n = 8). Groups 1 and 2 served as normal and negative controls, respectively. Diabetes was induced in test groups (2-6) using 150 mg/kg body weight (b.w) Alloxan monohydrate. Rats in groups 4-6 received of 200, 400 and 600 mg/kg b.w. EAFFZRB orally, respectively, for 21 days. Group 3 rats received 5 mg/kg b.w Glibenclamide. The effect of EAFFZRB on alterations in hematological, biochemical, and histological indices of study rats were assessed.

RESULTS

Extraction of 3500 g ethanol extract yielded 15.71 g EAFFZRB. HPLC fingerprint of EAFFZRB indicated presence of luteolin, rutin, quercetin, apigenin, cinnamic acid and catechin. Diabetes triggered significant (p < 0.05) alterations in b.w., hematological, biochemical and histological indices of test rats relative to normal control. Treatment with EAFFZRB (LD₅₀ = 3807.9 mg/kg b.w.) resulted in remarkable improvements in altered b.w. changes, hematological, biochemical and histological parameters of diabetic rats.

CONCLUSION

The study demonstrated the antidiabetic potential of EAFFZRB, providing scientific basis for traditional use of the plant in treatment of diabetes and its complications.

Pharmacology and toxicology of tannins

Tannins are an interesting class of polyphenols, characterized, in almost all cases, by a different degree of polymerization, which, inevitably, markedly influences their bioavailability, as well as biochemical and pharmacological activities. They have been used for the process of tanning to transform hides into leather, from which their name derives. For several time, they have not been accurately evaluated, but now researchers have started to unravel their potential, highlighting anti-inflammatory, antimicrobial, antioxidant and anticancer activities, as well as their involvement in cardiovascular, neuroprotective and in general metabolic diseases prevention. The mechanisms underlying their activity are often complex, but the main targets of their action (such as key enzymes modulation, activation of metabolic pathways and changes in the metabolic fluxes) are highlighted in this review, without losing sight of their toxicity. This aspect still needs further and better-designed study to be thoroughly understood and allow a more conscious use of tannins for human health.

Gut microbiota as a driver of the interindividual variability of cardiometabolic effects from tea polyphenols

Tea polyphenols have been extensively studied for their preventive properties against cardiometabolic diseases. Nevertheless, the evidence of these effects from human intervention studies is not always consistent, mainly because of a large interindividual variability. The bioavailability of tea polyphenols is low, and metabolism of tea polyphenols highly depends on individual gut microbiota. The accompanying reciprocal relationship between tea polyphenols and gut microbiota may result in alterations in the cardiometabolic effects, however, the underlying mechanism of which is little explored. This review summarizes tea polyphenols-microbiota interaction and its contribution to interindividual variability in cardiometabolic effects. Currently, only a few bacteria that can biodegrade tea polyphenols have been identified and generated metabolites and their bioactivities in metabolic pathways are not fully elucidated. A deeper understanding of the role of complex interaction necessitates fully individualized data, the ntegration of multiple-omics platforms and development of polyphenol-centered databases. Knowledge of this microbial contribution will enable the functional stratification of individuals in the gut microbiota profile (metabotypes) to clarify interindividual variability in the health effects of tea polyphenols. This could be used to predict individual responses to tea polyphenols consumption, hence bringing us closer to personalized nutrition with optimal dose and additional supplementation of specific microorganisms.

Green tea and obesity: Effects of catechins on the energetic metabolism

Obesity is a metabolic disease which has now reached epidemic proportions, becoming a major health, social, and economic problem worldwide. Untreated obesity is associated with decreased quality of life and is a significant risk factor for the development of other serious health problems, such as diabetes and cardiovascular diseases. For this reason, new approaches to prevent excess body mass and to support its reduction if necessary are being examined. Catechins extracted from green tea – especially epigallocatechin gallate (EGCG) – are one of the most widely investigated biologically active substances. In addition to the antioxidant, anti-inflammatory, and anticarcinogenic properties of the catechins, they also exhibit a role in maintaining normal fat mass and body mass. There are numerous research studies showing that regular green tea consumption is associated with lower body mass, BMI, and waist circumference. In vitro and animal experiments confirm beneficial effects of catechins on the energetic metabolism. These compounds lower lipid and carbohydrates absorption in the intestine. Additionally, they affect the energetic metabolism, lowering the rate of lipogenesis and adipogenesis, while stimulating lipolysis and fatty acid oxidation, and increasing energy expenditure. Moreover, it has been established that green tea catechins have an effect on the glucose uptake in the insulin-dependent manner – by GLUT4. The aim of the following paper was to review and summarize the literature data concerning the role of green tea catechins in the prevention and treatment of obesity.

Effect of green tea on glycemic control in patients with type 2 diabetes mellitus: A systematic review and meta-analysis

BACKGROUND AND AIMS

Several studies have investigated the potential beneficial effects of green tea in patients with type 2 diabetes mellitus (T2DM). Therefore, we aimed to perform a systematic review and meta-analysis of the randomized controlled trials (RCTs) that assessed the effect of supplementary intake of green tea on fasting plasma glucose (FPG), fasting insulin, hemoglobin A1c (HbA1c) and HOMA-IR in patients with T2DM.

METHODS

A systematic search was performed in Web of Science, PubMed and Scopus without any language and time restriction up to June 2019, to retrieve the related RCTs. Meta-analysis was carried out using both the random and fixed effects model where appropriate. I2 index was used to evaluate the heterogeneity.

RESULTS

Initial search yielded 780 publications. Fourteen articles were eligible. Our meta-analysis indicated that the supplementary intake of green tea had no significant effect on FPG, fasting insulin, HbA1c and HOMA-IR in patients with T2DM.

CONCLUSION

Results of the present systematic review and meta-analysis indicated that the supplementary intake of green tea had no significant effect on FPG, fasting insulin, HbA1c and HOMA-IR in patients with T2DM.

Effect of Green Tea on Anthropometric Indices and Body Composition in Patients with Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis

AIM

Previous studies that investigated the effect of green tea/green tea extract on anthropometric indices among type 2 diabetes mellitus (T2DM) patients found inconsistent results. Thus, in order to clarify the efficacy of green tea supplementation on anthropometric indices and body composition, we conducted a systematic review and meta-analysis to sum up the evidence of randomized controlled trials.

METHODS

A systematic search was conducted in the Scopus, ISI Web of Science and PubMed to find the related articles, up to June 2019. Meta-analysis was performed using the random effects model, and the I2 index was used to evaluate the heterogeneity.

RESULTS

Eleven articles were eligible. Our meta-analysis indicated that green tea consumption significantly decreased body weight, body mass index (BMI), and body fat (BF). The beneficial effect of green tea intake was observed in long-term intervention (>8 weeks), at lower doses of green tea (dosage ≤800 mg/day), and in overweight patients.

CONCLUSION

This study revealed the beneficial effects of green tea consumption in reducing body weight, BMI, and BF in T2DM patients. It should be noted that green tea was effective in long-term intervention, at lower doses of green tea, and in overweight patients.

Combination of Catechin, Epicatechin, and Rutin: Optimization of a novel complete antidiabetic formulation using a mixture design approach

Nowadays, synthetic chemical antidiabetic drugs, besides their therapeutic effects, present adverse effects that could be hard to handle over time. In the last decade, studies reported new alternative molecules with more health benefits and less adverse effects. The goal of this study is to optimize a new antidiabetic formulation using plant flavonoids: Catechin, Epicatechin, and Rutin. They are also a powerful antioxidant and anti-inflammatory molecules. A mixture design experiment will optimize their combination to obtain a new, safe multi-targets antidiabetic formulation making it a powerful combination for the management of diabetes and its complications. To study the variation of blood glucose level in response to the treatment over the time we performed an Oral Glucose Tolerance Test. The blood glucose level variations recorded as responses for the mixture design experiment. We used the molecules at a dose of 10 mg/kg. According to the software analysis, the prediction profiler showed us the optimum combination, and the result was a binary combination between Rutin and Epicatechin (25% and 75%, respectively). This combination prevented hyperglycemia and hypoglycemia, along with the best area under the curve, and after that, we validated it through a repeated oral administration on alloxan-induced diabetic mice for 28 d. Rutin, Catechin, and Epicatechin exhibit a potent antihyperglycemic activity, their synergistic combination validates a new formulation that could be a real candidate to conventional drugs.

Effect of Lactobacillus delbrueckii Subsp. lactis PTCC1057 on Serum Glucose, Fetuin-A ,and Sestrin 3 Levels in Streptozotocin-Induced Diabetic Mice

Intake of probiotic bacteria may improve or preserve insulin sensitivity. Fetuin-A and sestrin 3 have emerged as promising candidate biomarkers for crucial roles in insulin signaling pathway. Therefore, the effect of oral supplementation with the probiotic bacterium Lactobacillus delbrueckii subsp. lactis PTCC1057 on proteins involved in insulin signaling pathway was investigated in normal and streptozotocin (STZ)-induced diabetic mice. The 6-8-week-old female mice were divided into a non-diabetic control, diabetic control, and diabetic experimental and non-diabetic experimental groups (5 mice each group). Diabetic and non-diabetic experimental groups treated with 3 × 10⁷ CFU mL^-1 L. delbrueckii subsp. lactis PTCC1057 by gavage feeding approach daily for 28 days. Serum glucose, fetuin-A, and sestrin 3 levels were measured by standard methods. The result showed that oral administration of L. delbrueckii significantly decreased serum glucose in comparison to diabetic control group (P = 0.01). Serum fetuin-A level was higher in diabetic control group than non-diabetic group and oral administration of L. delbrueckii subsp. lactis PTCC1057 significantly decreased fetuin-A level in diabetic experimental group in comparison with non-diabetic groups (P = 0.001). Sestrin 3 level significantly was lower in diabetic control group than non-diabetic control group (P = 0.03) and it significantly increased in diabetic experimental group in comparison with diabetic control group after intervention of L. delbrueckii subsp. lactis PTCC1057 (P = 0.02). The results show that feeding the STZ-induced diabetic mice with L. delbrueckii subsp. lactis PTCC1057 terminated to decrease in fasting blood glucose and fetuin-A level and increase in serum sestrin 3 level. Therefore, the L. delbrueckii subsp. lactis PTCC1057 can be considered as excellent candidate for future studies on diabetes mellitus.

Effects of green tea consumption on glycemic control: a systematic review and meta-analysis of randomized controlled trials

Background

The results of human clinical trials investigating the effects of green tea on glycemic control are inconsistent.

Methods

We conducted a systematic review and meta-analysis of RCTs that examined the effects of green tea supplementation on glycemic control. A literature search in PubMed, Embase, and Cochrane Library databases for RCTs that investigated the effect of green tea consumption on glycemic control was performed up to February 2020. A random-effects model was used to estimate weighted mean difference (WMD) with 95% confidence intervals (CIs).

Results

Twenty-seven trials involving 2194 subjects were included in the meta-analysis. The pooled results showed that green tea significantly lowered fasting blood glucose by − 1.44 mg/dL (95%CI:-2.26, − 0.62 mg/dL; P < 0.001) with no obvious heterogeneity (I² = 7.7%). However, green tea consumption did not significantly affect fasting insulin and HbA1c values. The mean differences were − 0.46μIU/mL (95% CI: − 1.10, 0.17μIU/mL; P = 0.21) for fasting insulin and − 0.06%; (95% CI: − 0.12, 0.01%; P = 0.07) for HbA_1c concentrations. Heterogeneity was significant in fasting insulin (I² = 46.8%) and mild in HbA_1c (I² = 1.7%).

Conclusions

In short-term trials, green tea supplementation significantly reduced fasting glucose, but had no significant effect on fasting insulin and HbA_1c. Long-term trials assessing the effects of green tea supplementation on glycemic control are needed.

Effect of green tea extract on lipid profile in patients with type 2 diabetes mellitus: A systematic review and meta-analysis

BACKGROUND

Previous studies have indicated controversial results regarding the efficacy of green tea extract (GTE) in improving the lipid profile of type 2 diabetes mellitus (T2DM) patients. We aimed to conduct a systematic review and meta-analysis to pool data from randomized controlled trials (RCTs).

METHODS

A systematic search was performed in Web of Science, PubMed, and Scopus databases, without any language and time restriction until August 2019, to retrieve the RCTs which examined the effects of GTE on serum concentrations of high-density lipoprotein (HDL), low-density lipoprotein (LDL), triglyceride (TG) or total cholesterol (TC) in T2DM patients. Meta-analyses were carried out using a random effects model. I2 index was used to evaluate the heterogeneity.

RESULTS

Initial search yielded 780 publications. Of these, seven studies were eligible. The supplementary intake of GTE improved lipid profile by reducing serum TG concentrations in patients with T2DM. Meanwhile, subgroup analyses based on duration of interventions (≤8 and > 8 weeks) and intervention dosage (≤800 and > 800 mg/day) showed that the GTE supplementation longer than 8 weeks and in doses >800 mg/day resulted in a significant decrease in serum TG concentrations. Furthermore, intervention longer than 8 weeks with doses lower than 800 mg/day resulted in a significant reduction in serum TC concentrations.

CONCLUSION

In conclusion, present systematic review and meta-analysis revealed that the supplementary intake of GTE may improve lipid profile by reducing serum concentrations of TG in patients with T2DM. Furthermore, the results of our stratified analyses suggested that long-term GTE intervention may reduce serum concentrations of TG and TC.

Antidiabetic Effects of Flavan-3-ols and Their Microbial Metabolites

Diet is one of the pillars in the prevention and management of diabetes mellitus. Particularly, eating patterns characterized by a high consumption of foods such as fruits or vegetables and beverages such as coffee and tea could influence the development and progression of type 2 diabetes. Flavonoids, whose intake has been inversely associated with numerous negative health outcomes in the last few years, are a common constituent of these food items. Therefore, they could contribute to the observed positive effects of certain dietary habits in individuals with type 2 diabetes. Of all the different flavonoid subclasses, flavan-3-ols are consumed the most in the European region. However, a large proportion of the ingested flavan-3-ols is not absorbed. Therefore, the flavan-3-ols enter the large intestine where they become available to the colonic bacteria and are metabolized by the microbiota. For this reason, in addition to the parent compounds, the colonic metabolites of flavan-3-ols could take part in the prevention and management of diabetes. The aim of this review is to present the available literature on the effect of both the parent flavan-3-ol compounds found in different food sources as well as the specific microbial metabolites of diabetes in order to better understand their potential role in the prevention and treatment of the disease.

Effect of green tea consumption on blood lipids: a systematic review and meta-analysis of randomized controlled trials

Background

Strong epidemiologic evidence indicates that green tea intake is protective against hyperlipidemia; however, randomized controlled studies have presented varying results. In the present study, we aimed to conduct a literature review and meta-analysis to assess the effect of green tea on blood lipids.

Methods

PubMed, Embase, and the Cochrane Library were electronically explored from inception to September 2019 for all relevant studies. Random effect models were used to estimate blood lipid changes between green tea supplementation and control groups by evaluating the weighted mean differences (WMD) with 95% confidence intervals (CIs). The risk of bias for study was assessed using the Cochrane tool. Publication bias was evaluated using funnel plots and Egger’s tests.

Results

Thirty-one trials with a total of 3321 subjects were included in the meta-analysis. In general, green tea intake significantly lowered the total cholesterol (TC); WMD: − 4.66 mg/dL; 95% CI: − 6.36, − 2.96 mg/dL; P < 0.0001) and low-density lipoprotein (LDL) cholesterol (WMD:− 4.55 mg/dL; 95% CI: − 6.31, − 2.80 mg/dL; P < 0.0001) levels compared with those in the control. Green tea consumption did not affect high-density lipoprotein (HDL) cholesterol; however, it reduced the triglycerides compared with that in the control (WMD: − 3.77 mg/dL; 95% CI: − 8.90, 1.37 mg/dL; P = 0.15). In addition, significant publication bias from funnel plots or Egger’s tests was not evident.

Conclusions

Collectively, consumption of green tea lowers LDL cholesterol and TC, but not HDL cholesterol or triglycerides in both normal weight subjects and those who were overweight/obese; however, additional well-designed studies that include more diverse populations and longer duration are warranted.

Effect of green tea supplementation on blood pressure: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Although evidence from animal and observational studies has supported the beneficial effects of green tea intake for lowering blood pressure (BP), randomized placebo-controlled trials (RCTs) have yielded conflicting results. In this meta-analysis of RCTs, we aimed to assess the effects of green tea supplementation on measures of BP control.

METHODS

The PubMed, Embase, and Cochrane Library databases were electronically searched from inception to August 2019 for all relevant studies. The results were pooled using the generic inverse-variance method with random-effects weighting and expressed as mean differences (MDs) with 95% confidence intervals (CIs). The quality of studies was assessed using the Jadad score. Publication bias was evaluated using funnel plots, Egger test, and Begg test.

RESULTS

Twenty-four trials with 1697 subjects were included in the meta-analysis. The pooled results showed that green tea significantly lowered systolic BP (SBP; MD: -1.17 mm Hg; 95%CI: -2.18 to -0.16mm Hg; P = .02) and diastolic BP (DBP; MD: -1.24 mm Hg; 95%CI:-2.07 to -0.40mm Hg; P = .004). Significant heterogeneity was found for both SBP (I = 43%) and DBP (I = 57%). In addition, no evidence of significant publication bias was found from funnel plots or Egger test (P = .674 and P = .270 for SBP and DBP, respectively).

CONCLUSION

Overall, green tea significantly reduced SBP and DBP over the duration of the short-term trials. Larger and longer-term trials are needed to further investigate the effects of green tea supplementation on BP control and clinical events.

The effect of green tea on C-reactive protein and biomarkers of oxidative stress in patients with type 2 diabetes mellitus: A systematic review and meta-analysis

INTRODUCTION

The beneficial effects of green tea on regulating insulin sensitivity and preventing the development of type 2 diabetes mellitus (T2DM) have been identified.

OBJECTIVES

We aimed to investigate the effect of green tea on serum levels of C-reactive protein (CRP) and biomarkers of oxidative stress in patients with T2DM.

METHODS

A systematic search was performed in the ISI Web of science, PubMed and Scopus to find articles related to the effect of the green tea on CRP, malondealdehyde (MDA) and total antioxidant capacity (TAC) in T2DM patients, up to June 2019. There was no language and time limitation. Meta-analyses were performed using both the random and fixed effects model where appropriate, and I2 index was used to evaluate the heterogeneity.

RESULTS

Initial search yielded 780 publications. Eight articles with 614 T2DM patients were eligible. Following green tea consumption, CRP levels significantly decreased (weighted mean difference (WMD): -5.51 mg/dl, 95% CI: -9.18 to -1.83, p = 0.003) compared with the controlled group. Green tea consumption had no significant effect on plasma levels of TAC and MDA (0.02 mg/dl, CI: -0.06 to 0.10; -0.14 mg/dl, CI: -0.40 to 0.12; respectively).

CONCLUSION

This systematic review and meta-analysis indicated that green tea significantly reduced the circulating levels of CRP, whereas, it had no significant effect on MDA and TAC. Overall, green tea can be considered as a healthy drink to reduce CRP levels in T2DM patients.

Effects of timing of acute catechin-rich green tea ingestion on postprandial glucose metabolism in healthy men

Green tea polyphenols, particularly catechins, decrease fasting and postprandial glucose. However, no studies have compared the timing of green tea ingestion on glucose metabolism and changes in catechin concentrations. Here, we examined the effects of timing of acute catechin-rich green tea ingestion on postprandial glucose metabolism in young men. Seventeen healthy young men completed four trials involving blood collection in a fasting state and at 30, 60, 120, and 180 min after meal consumption in a random order: 1) morning placebo trial (09:00 h; MP trial), 2) evening placebo trial (17:00 h; EP trial), 3) morning catechin-rich green tea trial (09:00 h; MGT trial), and 4) evening catechin-rich green tea trial (17:00 h; EGT trial). The concentrations of glucose at 120 min (P=.031) and 180 min (P=.013) after meal intake were significantly higher in the MGT trials than in the MP trials. Additionally, the concentration of glucose was significantly lower in EGT trials than in the EP trials at 60 min (P=.014). Moreover, the concentrations of glucose-dependent insulinotropic polypeptide were significantly lower in the green tea trials than in the placebo trials at 30 min (morning: P=.010, evening: P=.006) and 60 min (morning: P=.001, evening: P=.006) after meal intake in both the morning and evening trials. Our study demonstrated that acute ingestion of catechin-rich green tea in the evening reduced postprandial plasma glucose concentrations.

Effects and Mechanisms of Tea Regulating Blood Pressure: Evidences and Promises

Cardiovascular diseases have overtaken cancers as the number one cause of death. Hypertension is the most dangerous factor linked to deaths caused by cardiovascular diseases. Many researchers have reported that tea has anti-hypertensive effects in animals and humans. The aim of this review is to update the information on the anti-hypertensive effects of tea in human interventions and animal studies, and to summarize the underlying mechanisms, based on ex-vivo tissue and cell culture data. During recent years, an increasing number of human population studies have confirmed the beneficial effects of tea on hypertension. However, the optimal dose has not yet been established owing to differences in the extent of hypertension, and complicated social and genetic backgrounds of populations. Therefore, further large-scale investigations with longer terms of observation and tighter controls are needed to define optimal doses in subjects with varying degrees of hypertensive risk factors, and to determine differences in beneficial effects amongst diverse populations. Moreover, data from laboratory studies have shown that tea and its secondary metabolites have important roles in relaxing smooth muscle contraction, enhancing endothelial nitric oxide synthase activity, reducing vascular inflammation, inhibiting rennin activity, and anti-vascular oxidative stress. However, the exact molecular mechanisms of these activities remain to be elucidated.

Flavonoids and Insulin-Resistance: From Molecular Evidences to Clinical Trials

Insulin-resistance is one of the main factors responsible for the onset and progression of Metabolic Syndrome (MetS). Among all polyphenols, the effects of flavonoids and their main food sources on insulin sensitivity have been widely evaluated in molecular and clinical studies. The aim of this review is to analyse the data observed in vitro, in vivo and in clinical trials concerning the effects of flavonoids on insulin resistance and to determine the molecular mechanisms with which flavonoids interact with insulin signaling.

A Selective Role of Dietary Anthocyanins and Flavan-3-ols in Reducing the Risk of Type 2 Diabetes Mellitus: A Review of Recent Evidence

Type 2 diabetes mellitus (T2DM) is the most common form of DM and its prevalence is increasing worldwide. Because it is a progressive disease, prevention, early detection and disease course modification are possible. Diet plays a critical role in reducing T2DM risk. Therapeutic dietary approaches routinely recommend diets high in plant foods (i.e., vegetables, fruits, whole-grains). In addition to essential micronutrients and fiber, plant-based diets contain a wide-variety of polyphenols, specifically flavonoid compounds. Evidence suggests that flavonoids may confer specific benefits for T2DM risk reduction through pathways influencing glucose absorption and insulin sensitivity and/or secretion. The present review assesses the relationship between dietary flavonoids and diabetes risk reduction reviewing current epidemiology and clinical research. Collectively, the research indicates that certain flavonoids, explicitly anthocyanins and flavan-3-ols and foods rich in these compounds, may have an important role in dietary algorithms aimed to address diabetes risk factors and the development of T2DM.

Effects of Coffee and Tea Consumption on Glucose Metabolism: A Systematic Review and Network Meta-Analysis

Prospective cohort studies have described an association between coffee or tea consumption and the risk of developing diabetes. However, whether coffee or tea improves glucose metabolism remains uncertain. We investigated the effect of coffee and tea on glucose metabolism by conducting a systematic review and meta-analysis of randomized controlled trials. Electronic databases were searched for articles published up 19 February 2017. The primary endpoint was the mean difference in post-intervention fasting blood glucose (FBG) levels between the groups. Of 892 citations screened, 27 studies (1898 participants) were included in our meta-analysis. A network meta-analysis suggested that green tea, but not caffeinated/decaffeinated coffee or black tea, may reduce FBG levels, compared with placebo/water (−2.10 mg/dL; 95% confidence interval (CI), −3.96 to −0.24 mg/dL; p = 0.03; moderate quality of evidence). In a subgroup analysis, the effect of green tea on FBG levels was statistically significant only in studies with a mean age of < 55-years-old or Asian-based studies. The oolong tea group also showed a significant decrease in FBG, but the quality of evidence was very low. In conclusion, green tea consumption might decrease FBG levels, especially in < 55-year-olds or Asian-based populations.

A phase I single-blind clinical trial to evaluate the safety of oil palm phenolics (OPP) supplementation in healthy volunteers

Plant phenolics are being increasingly consumed globally with limited scientific and clinical evidence pertaining to safety and efficacy. The oil palm fruit contains a cocktail of phenolics, and palm oil production results in high volumes of aqueous by-products enriched in phenolics and bioactives. Several lines of evidence from in vitro and in vivo animal studies confirmed that the aqueous extract enriched in phenolics and other bioactives collectively known as oil palm phenolics (OPP) is safe and has potent bioactivity. A phase one clinical trial was conducted to evaluate the safety and effects of OPP in healthy volunteers. In this single-blind trial, 25 healthy human volunteers were supplemented with 450 mg gallic acid equivalent (GAE)/day of OPP or control treatments for a 60-day period. Fasting blood and urine samples were collected at days 1, 30 and 60. Medical examination was performed during these trial interventions. All clinical biochemistry profiles observed throughout the control and OPP treatment period were in the normal range with no major adverse effect (AE) or serious adverse effect (SAE) observed. Additionally, OPP supplementation resulted in improvement of total cholesterol and LDL-C levels, compared to the control treatment. The outcomes support our previous observations that OPP is safe and may have a protective role in reducing cholesterol levels.

Diabetes and Alzheimer's Disease: Can Tea Phytochemicals Play a Role in Prevention?

Dementia and diabetes mellitus are prevalent disorders in the elderly population. While recognized as two distinct diseases, diabetes has more recently recognized as a significant contributor to risk for developing dementia, and some studies make reference to type 3 diabetes, a condition resulting from insulin resistance in the brain. Alzheimer's disease, the most common form of dementia, and diabetes, interestingly, share underlying pathological processes, commonality in risk factors, and, importantly, pathways for intervention. Tea has been suggested to possess potent antioxidant properties. It is rich in phytochemicals including, flavonoids, tannins, caffeine, polyphenols, boheic acid, theophylline, theobromine, anthocyanins, gallic acid, and finally epigallocatechin-3-gallate, which is considered to be the most potent active ingredient. Flavonoid phytochemicals, known as catechins, within tea offer potential benefits for reducing the risk of diabetes and Alzheimer's disease by targeting common risk factors, including obesity, hyperlipidemia, hypertension, cardiovascular disease, and stroke. Studies also show that catechins may prevent the formation of amyloid-β plaques and enhance cognitive functions, and thus may be useful in treating patients who have Alzheimer's disease or dementia. Furthermore, other phytochemicals found within tea offer important antioxidant properties along with innate properties capable of modulating intracellular neuronal signal transduction pathways and mitochondrial function.

Epigallocatechin gallate (EGCG) reduces the intensity of pancreatic amyloid fibrils in human islet amyloid polypeptide (hIAPP) transgenic mice

The formation of amyloid fibrils by human islet amyloid polypeptide protein (hIAPP) has been implicated in pancreas dysfunction and diabetes. However, efficient treatment options to reduce amyloid fibrils in vivo are still lacking. Therefore, we tested the effect of epigallocatechin gallate (EGCG) on fibril formation in vitro and in vivo. To determine the binding of hIAPP and EGCG, in vitro interaction studies were performed. To inhibit amyloid plaque formation in vivo, homozygous (tg/tg), hemizygous (wt/tg), and control mice (wt/wt) were treated with EGCG. EGCG bound to hIAPP in vitro and induced formation of amorphous aggregates instead of amyloid fibrils. Amyloid fibrils were detected in the pancreatic islets of tg/tg mice, which was associated with disrupted islet structure and diabetes. Although pancreatic amyloid fibrils could be detected in wt/tg mice, these animals were non-diabetic. EGCG application decreased amyloid fibril intensity in wt/tg mice, however it was ineffective in tg/tg animals. Our data indicate that EGCG inhibits amyloid fibril formation in vitro and reduces fibril intensity in non-diabetic wt/tg mice. These results demonstrate a possible in vivo effectiveness of EGCG on amyloid formation and suggest an early therapeutical application.

Beneficial metabolic effects of dietary epigallocatechin gallate alone and in combination with exendin-4 in high fat diabetic mice

OBJECTIVE

Significant attempts are being made to generate multifunctional, hybrid or peptide combinations as novel therapeutic strategies for type 2 diabetes, however this presents key challenges including design and pharmaceutical development. In this study, we evaluated metabolic properties of oral nutritional supplement epigallocatechin gallate (EGCG) in combination with GLP-1 agonist exendin-4 in a mouse model of dietary-induced diabetes and obesity.

METHODS

EGCG, exendin-4 or combination of both were administered twice-daily over 28 days to high fat (HF) mice on background of low-dose streptozotocin. Energy intake, body weight, fat mass, glucose tolerance, insulin sensitivity, lipid profile, biochemical and hormone markers, and islet histology were examined.

RESULTS

All treatment groups exhibited significantly reduced body weight, fat mass, circulating glucose and insulin concentrations, and HbA1c levels which were independent of changes in energy intake. Similarly, there was marked improvement in glycaemic control, glucose-stimulated insulin release, insulin sensitivity, total cholesterol and triglycerides, with most prominent effects observed following combination therapy. Circulating corticosterone concentrations and 11beta-hydroxysteroid dehydrogenase type1 (11β-HSD1) staining (in pancreas) were beneficially decreased without changes in circulating interleukin 6 (IL-6), alanine transaminase (ALT) and glutathione reductase. Combination therapy resulted in increased islet area and number, beta cell area, and pancreatic insulin content. Generally, metabolic effects were much more pronounced in mice which received combination therapy.

CONCLUSIONS

EGCG alone and particularly in combination with exendin-4 exerts positive metabolic properties in HF mice. EGCG may be useful dietary adjunct alongside GLP-1 mimetics in treatment of diabetes and related disorders.

Inhibition of α-glucosidase and α-amylase by flavonoid glycosides from Lu'an GuaPian tea: molecular docking and interaction mechanism

Inhibition of α-glucosidase and α-amylase by flavonoid glycosides from Lu'an GuaPian tea.

Polyphenols and their effects on diabetes management: A review

Background: Type 2 diabetes is a growing public health problem and is associated with increased morbidity and mortality. The worldwide prevalence of type 2 diabetes is rising. Polyphenols, such as flavonoids, phenolic acid, and stilbens, are a large and heterogeneous group of phytochemicals in plant-based foods. In this review, we aimed at assessing the studies on polyphenols and diabetes management. Methods: A literature search in the PubMed, EMBASE, Scopus, and ISI Web of Science databases was conducted to identify relevant studies published from 1986 to Jan 2017. Results: Several animal models and a limited number of human studies have revealed that polyphenols decrease hyperglycemia and improve acute insulin secretion and insulin sensitivity. The possible mechanisms include decrease in glucose absorption in the intestine, inhibition of carbohydrates digestion, stimulation of insulin secretion, modulation of glucose release from the liver, activation of insulin receptors and glucose uptake in insulin-sensitive tissues, modulation of intracellular signaling pathways, and gene expression. Conclusion: Growing evidence indicates that various dietary polyphenols may influence blood glucose at different levels and may also help control and prevent diabetes complication. However, we still need more clinical trials to determine the effects of polyphenols- rich foods, their effective dose, and mechanisms of their effects in managing diabetes.

The Effectiveness of Green Tea or Green Tea Extract on Insulin Resistance and Glycemic Control in Type 2 Diabetes Mellitus: A Meta-Analysis

Green tea or green tea extract (GT/GTE) has been demonstrated to reduce insulin resistance and improve glycemic control. However, evidence for this health beneficial effect is inconsistent. This systematic review evaluated the effect of GT/GTE on insulin resistance and glycemic control in people with pre-diabetes/type 2 diabetes mellitus (T2DM). Ovid MEDLINE, Embase, AMED, Web of Science, and the Cochrane Library were searched up to April 2017 for randomised controlled trials of participants with pre-diabetes or T2DM, where the intervention was GT/GTE. Meta-analysis was performed to assess the standardised mean difference (SMD) in biomarkers of insulin resistance and glycemic control between GT/GTE and placebo groups. Six studies (n=382) were pooled into random-effects meta-analysis. Overall, no differences were found between GT/GTE and the placebo for glycosylated hemoglobin (HbA1c: SMD, -0.32; 95% confidence interval [CI], -0.86 to 0.23), homeostatic model assessment for insulin resistance (HOMA-IR: SMD, 0.10; 95% CI, -0.17 to 0.38), fasting insulin (SMD, -0.25; 95% CI, -0.64 to 0.15), and fasting glucose (SMD, -0.10; 95% CI, -0.50 to 0.30). No evidence support the consumption of GT/GTE could reduce the levels of HbA1c, HOMA-IR, fasting insulin, or fasting glucose in people with pre-diabetes/T2DM. However, the studies included were small and of varying quality.

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.