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.

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.

Effect of Green Tea Supplementation on Antioxidant Status in Adults: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

It is well-established that green tea supplementation has antioxidant properties. However, whether green tea supplementation leads to oxidative stress reduction remains unclear, as clinical investigations on this subject have yielded inconsistent outcomes. Consequently, we aimed to determine the effects of green tea supplementation on oxidative stress in adults. A systematic search of English language publications up to 21 August 2021 was carried out in PubMed, Scopus, Embase, and ISI Web of Science, utilizing pertinent keywords. These searches included randomized controlled trials (RCTs) evaluating the relationship between green tea supplementation, malondialdehyde (MDA), and total antioxidant capacity (TAC) in adults. A random-effects model was used to estimate the weighted mean difference (WMD) and 95% confidence intervals (95% CI). Meta-regression and non-linear dose-response analyses were performed to investigate the association between the dosage of green tea (mg/day) and the duration of the intervention (weeks) with pooled effect size. Sixteen RCTs with seventeen arms including 760 participants met the inclusion criteria. Our results indicated that green tea supplementation had significant effects on TAC (weighted mean difference [WMD]: 0.20 mmol/L; 95% CI: 0.09, 0.30, p < 0.001) and significant heterogeneity between studies (I² = 98.6%, p < 0.001), which was largely related to gender and body mass index (BMI). Subgroup analysis in TAC identified a significant relationship except with low dose supplementation and obese individuals. No relationship between MDA and green tea supplementation was observed in any subgroups; however, meta-regression analysis revealed a linear inverse association between the dosage and significant change in MDA (r = −2117.18, p = 0.017). Our outcomes suggest that green tea supplementation improves TAC and affects MDA based on the dose of the intervention in adults. Future RCTs with longer durations are needed to expand our findings.

The effect of green tea supplementation on obesity: A systematic review and dose-response meta-analysis of randomized controlled trials

The effects of green tea (GT) in obese subjects have been evaluated in different studies, but no consensus has been obtained due to the heterogeneity of the results. The dosage, the type of extract, and the duration of the intervention are the main contributors to the heterogeneity of the results. Therefore, the present systematic review and meta-analysis aimed to evaluate the efficacy and dose-response relationship of GT. Several databases were searched from inception to September 2019 to identify clinical trials that examined the influence of GT supplements on obesity indices in humans. Combined results using the random-effects model indicated that body weight (WMD: -1.78 kg, 95% CI: -2.80, -0.75, p = .001) and body mass index (BMI) (WMD: -0.65 kg/m2 , 95% CI: -1.04, -0.25, p = .001) did change significantly following GT administration. The reduction in waist circumference (WC) after GT consumption was significant in subjects in trials employing GT ≥800 mg/day (WMD: -2.06 cm) and with a treatment duration <12 weeks (WMD: -2.39 cm). Following the dose-response evaluation, GT intake did alter body weight, with a more important reduction when the GT dosage was <500 mg/day and the treatment duration was of 12 weeks. The results of present meta-analysis study support the use of GT for the improvement of obesity indices. Thus, we suggest that the use of GT can be combined with a balanced and healthy diet and regular physical exercise in the management of obese patients.

Green tea influence on iron overload in thalassemia intermedia patients: a randomized controlled trial

Background: Although iron chelation therapies have been available for many years for thalassemia intermedia patients, iron accumulation remains the major cause of death. Therefore, the need for additional chelation options is in demand. This randomized controlled study aimed to understand the effects of green tea on iron balance in thalassemia intermedia patients. Methods: Using a random selection method, 141 thalassemia intermedia patients were initially screened for inclusion in this trial; only 68 patients included after applying exclusion criteria. Two equal groups were generated (n=34/group): green tea (three cups/day after meals) + usual treatment (deferasirox iron chelator and on demand blood transfusion); and control (only usual treatment). The study lasted for a period of 12 months. Patients failing to comply to the trial methodology were excluded, leaving a final total of 29 patients in the green tea group and 28 patients in the control group. Liver iron concentration, and serum ferritin were assessed at baseline and 12 months, while hemoglobin levels were assessed monthly. Results: At baseline, both groups were matched regarding general demographics. At 12 months, the net drop of liver iron concentration in the green tea group (7.3 mg Fe/g dry weight) was significantly higher than the control group (4.6 mg Fe/g dry weight) (p<0.05). This was also seen with serum ferritin; net reduction in green tea and control groups were 1289 ng/ml and 871 ng/ml, respectively (p<0.05). Hemoglobin levels were slightly higher in the green tea group compared with the control group, but this was not significant. Conclusions: Regular green tea consumption had a significant capability to improve iron deposition in thalassemia intermedia patients who already undergo deferesirox iron chelation therapy. Trial registration: UMIN-CTR Clinical Trials Registry, UMIN000040841 (retrospectively registered June 21, 2020).