Abstract
Background
Overweight and obesity as main health problems harm human beings worldwide. The number of people diagnosed with overweight and obese is gradually increasing. Green tea catechin has been reported to effectively help control body weight in overweight and obese population, and is protectively against the blood pressure and lipids in people with type 2 diabetes and metabolic syndrome.
Methods
We retrieved 4 English databases (PubMed, Web of science, Cochrane, Scoups) from inception to April 20, 2023. Two reviewers independently determined eligibility, assessed the reporting quality of included studies, and extracted the data. Data were extracted from eleven studies. The results were presented with the weighted mean differences (WMDs), and the confidence intervals (CIs) was 95 %. The random-effects or fixed-effects model was applied according to the heterogeneity. The subgroup analysis was used to identify the source of heterogeneity. Publication bias was evaluated using funnel plots, Egger's test, and Begg's test.
Results
Eleven randomized controlled trials (RCTs) inclusion studies were screened from 3072 literature articles, involving 613 overweight and obese patients. After combining all studies, it was found that in overweight and obese people green tea catechin could reduce waist circumference (WC) (pooled WMD = −1.37 cm, 95 % CI: −2.52 to −0.22 cm, p = 0.019), and triglyceride (TG) (pooled WMD = −0.18 mmol/L, 95 % CI: −0.35 to −0.02 mmol/L, p = 0.032), and increase high density lipoprotein cholesterol (HDL-c) (pooled WMD = 0.07 mmol/L, 95 % CI: 0.01–0.14 mmol/L, p = 0.031).
Conclusion
Green tea catechin supplement effectively reduced WC and TG levels and improved HDL-c levels. However, it did not show the significant effect on the blood pressure in overweight and obese people. The present meta-analysis showed a moderate benefit of green tea catechin supplementation on lipid profiles in overweight and obese people.
Keywords: Green tea catechin, Blood pressure, Lipids, Overweight, Obese
1. Introduction
Obesity is a global problem, with obesity rates increasing year by year worldwide [1]. According to the World Health Organization, more than 1.9 billion adults aged 18 and older were overweight worldwide, and more than 650 million adults were obese. Thirty-nine percent of adults aged 18 years and older (39 % of men and 40 % of women) were overweight, and 13 % of the adult population (11 % of men and 15 % of women) were with obese. Studies have shown that obesity is a major risk factor for multiple chronic diseases, such as cardiovascular disease [2], hyperlipidemia [3], and diabetes [4]. The various diseases caused by obesity increase the burden of disease medical care. The economic impact of overweight and obesity is expected to rise to 3.29 % of the global GDP by 2060 [5]. Currently, studies were conducted in overweight and obese people, such as lifestyle change, behavioral therapy [6], medication, and surgery [7]. Dietary supplements play a role in improving overweight and obesity. Recently, the study showed [8] that green tea consumption has displayed the beneficial with reducing low density lipoprotein cholesterol (LDL-c) and total cholesterol (TC) levels. Furthermore, a reticular meta-analysis [9] showed that inulin, rich in green tea catechin, was a good choice for weight loss in overweight and obese patients.
Green tea is one of the most frequently cited beverages in the world [10], and tea has antioxidant properties and contains trace amounts of protein, carbohydrates, amino acids, lipids, vitamins, and minerals [11]. It also contains a wide range of compounds, but mainly polyphenols occupy the tea aroma and beneficial health effects. The main substance in green tea polyphenols is catechin, which is 25–35 % of the dry weight of green tea [12]. Green tea catechin includes (−)-epigallocatechin-3-gallate (EGCG), (−)-epicatechin-3-gallate (ECG), (−)-epigallocatechin (EGC) and (−)-epicatechin (EC) [10]. Among them, epigallocatechin gallate (EGCG) is the main active ingredient, with the most abundant content in catechin. It accounts for 50%–70 % of the catechins [12].
EGCG has been extensively studied and is considered as an effective nutritional supplement responsible for many health benefits, especially the antidiabetic [13], antiangiogenic and antimutagenic properties [14], including cholesterol-lowering [15], antimicrobial [16], prevention of Alzheimer's disease [17,18] and anti-aging [19] activities. A meta-analysis showed that green tea or green tea extract(GTE) supplementation had a significant effect on both systolic blood pressure (SBP) and diastolic blood pressure (DBP) when compared to the placebo in overweight and obese patients [20]. However, in another meta-analysis [21] showed that green tea catechin supplementation effect on the blood pressure was not significant after the subgroup analysis of overweight and obese patients. In animal experiments, supplementation with green tea extract for three months at specific doses reduced TC, triglycerides (TG), and low density lipoprotein cholesterol (LDL-c) levels in mice [22]. It has been shown that EGCG is achieved by reducing adipocyte differentiation and proliferation during adipogenesis. In population trials, green tea has significantly reduced plasma TC and LDL-c levels in overweight or obese people [21]. However, another study found that green tea catechin supplementation reduced triglyceride levels in obese people, with no effect on other serum lipid indicators [23].
Overall, the effects of the main active compound, EGCG, in green tea, on reducing obesity and improving metabolic status still remain controversial. Studies on whether green tea catechin can improve blood pressure and lipids in overweight and obese people vary. Moreover, no studies were conducted in overweight and obese adults with pooled analysis of green tea catechin on blood pressure and lipids so far. To elucidate the efficacy of green tea catechin in preventing blood pressure and dyslipidemia in overweight and obese adults. This study investigated the effects of green tea catechin on blood pressure and lipids in overweight and obese people by meta-analysis.
2. Methods
The current systematic review and meta-analysis were conducted based on the 2020 PRISMA guidelines [24]. The study protocol was submitted and approved in the international prospective register of systematic reviews database (PROSPERO) under the registration number: CRD42023417157.
2.1. Literature search strategy
We conducted electronic searches in the following data-bases: PubMed, Web of science, Scoups, and Cochrane libraries, from inception to October 31, 2022. Keywords searched were either "green tea catechin", "catechin" or "green tea extract" and "blood pressure" or "blood lipid". To search for the exact terms, quotes were used, and parentheses were used to search for group search terms. Advanced search is designed by using the Boolean operator (AND and OR), and by searching for all words derived from a keyword, using an asterisk. After searching all relevant RCTs, reference lists were also checked to find more relevant trials. The search was not restricted to publication time, gender, and language. We also performed a manual search of the relevant literatures to ensure that the retrieved literature was complete and accurate. All articles found were exported to EndNote X20 to read the title and abstract separately by the two reviewers (Ying Wang and Hui Xia). Two authors extracted the data separately, and the differences between the literature search and the literature collection were resolved through discussion and professional consultation.
2.2. Inclusion and exclusion criteria for the study
Inclusion criteria: (1) the study design was a randomized controlled design; (2) adult overweight and obese subjects ingesting catechin supplements; (3) the trial reported effects on SBP, SDP, TC, TG, LDL-c, and HDL-c; (4) the only difference between the test and control groups was the use of green tea catechin or green tea extracts; (5) control measures were either a placebo or a blank control. The exclusion criteria are as follows: (1) included trials of children or pregnant women; (2) studies of adding green tea catechin as a mixture; (3) the control group is low-dose catechin or other possible factors that may affect the results; (4) trials without details of the EGCG content of green tea catechin; and (5) trials with no accurate data.
2.3. Selection of studies and data extraction
The study selected RCTs, the data extraction by the two-person entry method, check and check to ensure that the data is accurate. The data of the 11 selected articles were extracted from BMI, waist circumference, blood pressure index (SBP, DBP), and blood lipid index (TC, TG, HDL-c, and LDL-c). Two reviewers (Ying Wang and Hui Xia) independently extracted the following characteristics of the 11 trials: first author, year, study area, study design, sample size (male/female), age, EGCG dose, baseline and endpoints of different blood pressure and lipid levels. After a rigorous discussion, results of the data extraction are summarized.
2.4. Assessment of the literature quality and the risk of bias
Two reviewers (Wang Ying and Hui Xia) evaluated the literature quality of the literature according to the improved Jadad scoring method, and rated the screened literature from four aspects (generation of random sequences, randomization hiding, blindness, loss to follow-up and withdrawal). Also, included risk of bias was independently assessed using the Cochrane Risk of bias tool, which assessed the risk of bias based on random sequence generation, allocation concealment, object and person blinding, outcome assessment blinding, incomplete outcome data, and selective reporting.
2.5. Statistical analyses
STATA15.0 were used to analyze the data, summarize and analyzed the results of the control group and the test group. Data presented in milligrams per deciliter were transformed to millimoles per liter by dividing by 38.66 for HDL-c, LDL-c, and TC while 88.6 for TG. We compare the results with the test group by calculating WMD. The pooled results were shown with the calculated WMD.
Two-sided of p < 0.05 was considered statistical significance. Heterogeneity between trials was assessed by I2 and chi-squared statistics, either I2 > 50 % or a p-value <0.05 was considered as significant heterogeneity. In addition, a fixed-effects model was adopted to conduct the meta-analysis if statistical heterogeneity was present (p > 0.05 or I2 < 50 %); otherwise, a random-effects model was used. Subgroup analyses were performed to explore the sources of heterogeneity. In addition, subgroup analysis of the results according to gender, intervention dose, with and without other weight management, the data heterogeneity and sensitivity differences were analyzed. The leave-one-out method was used for sensitivity analyses to assess the impact of each research on the overall effect size. Funnel plots and Egger regression test were used to assess publication bias. To quantify the publication bias, the Egger's test and Begg's test were used [25]. The trim and fill approach was also used to rectify the funnel asymmetry induced by publication bias. A statistically significant difference was established by p < 0.05.
3. Results
3.1. Search results and characteristics of included studies
The literature search resulted in 3072 citations, 38 initially deleted for repeated publication, 2987 publications were excluded based on titles and abstracts, 15 unavailable, 4 for mixture interventions, 8 for unavailable data, 9 for non-randomized controlled trials, and 11 ultimately included in the study. A flowchart of the search strategy and study selection is shown in Fig. 1.
Fig. 1.
Flow diagram for selected trials. (a) Forest plot of effects of BMI (b) Forest plot of effects of waist circumference (c) Forest plot of effects of SBP (d) Forest plot of effects of DBP.
Table 1 summarizes the basic information of the literature, including the first author, year of publication, sample size, intervention substance, intervention dose, duration of intervention, type of placebo, etc [[26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36]].In total, the study included 613 participants, of which 313 participants were randomized to the trial group, and 300 participants were randomly assigned to the placebo-control group. In all included studies, the analysis of baseline characteristics of participants showed no significant differences between the control and trial groups in age, body weight, BMI, blood pressure, blood lipid index, and so on.
Table 1.
Characteristics of included studies.
| No. | First author | Year | Location | Number (Intervnetion/Control) | Intervention | Control | Study design | Time | Dose | Health condition | Weight management |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | I-Ju Chen [18] | 2016 | China | 77(39/38) | Green tea Extract capsules | Cellulose | Randomized double-blind control | 12 weeks | 857 mg EGCG | Health | No |
| 2 | Joanna Suliburska [19] | 2012 | Poland | 46(23/23) | Green tea Extract capsules | Cellulose | Randomized double-blind control | 3 months | 208 mg EGCG | Health | No |
| 3 | Juan Mielgo-Ayuso [20] | 2014 | Spain | 83(43/40) | Green tea Extract | Lactin | Randomized double-blind control | 12 weeks | 300 mg EGCG | Health | Yes |
| 4 | Chung-Hua Hsu [21] | 2008 | China | 78(41/37) | Green tea Extract capsules | Cellulose | Randomized double-blind control | 12 weeks | 400 mg EGCG | Health | No |
| 5 | Justin D. Roberts [22] | 2021 | UK | 18(9/9) | Green tea Extract | Cellulose | Randomized single blind control | 8 weeks | 400 mg EGCG | Health | Yes |
| 6 | Chung-Hua Hsu [23] | 2011 | China | 68(35/33) | Green tea Extract | Cellulose | Randomized double-blind control | 16 weeks | 857 mg EGCG | Type 2 diabetes | No |
| 7 | K. Diepvens [24] | 2006 | Netherlands | 46(23/23) | Green tea Extract | Cellulose | Randomized double-blind control | 12 weeks | 267 mg EGCG | Health | Yes |
| 8 | Joanna Bajerska [25] | 2015 | Poland | 44(23/21) | Green tea extract additive | Blank | Randomized single blind control | 12 weeks | 242 mg EGCG | Health | Yes |
| 9 | Tengfei Zhang [26] | 2020 | China | 24(12/12) | Green tea Extract | Cellulose | Randomized double-blind control | 12 weeks | 300 mg EGCG | Health | No |
| 10 | Pawel Bogdanski [27] | 2012 | Poland | 56(28/28) | GTE capsules | Cellulose | Randomized double-blind control | 3 months | 208 mg EGCG | Hypertension | No |
| 11 | Lin-Huang Huang [28] | 2018 | China | 73(37/36) | GTE capsules | Cellulose | Randomized, double-blind, cross-over control | 6 weeks | 857 mg EGCG | High LDL-c | No |
Table 1 shows that most of the intervention groups were green tea catechin extract capsules, one test was a green tea extract additive, and the control measure was lactose or microcrystalline cellulose. There were 2 trials with the intervention time of <12 weeks, and the rest of the intervention time was greater than or equal to 12 weeks. Five trials of the intervention dose had EGCG content greater than 300 mg, and six trials had EGCG content less than or equal to 300 mg. Furthermore, all 11 included literatures were prospective, randomized, placebo-controlled trials, with one a randomized crossover trial and one an intention-to-treat analysis trial.
3.2. Methodological quality and risk of bias
The quality of the literature was evaluated by JADAD scores, with a median quality score of 7 (ranging from 4 to 7). All included literature belonged to high quality literature according to the scoring rules.
The risk of bias in included literatures was assessed by the Cochrane risk bias. The risks of bias in the study are presented in Table 2. Overall, all trials (100 %) clearly described the process of randomization and how the allocation was hidden.
Table 2.
Cochrane risk of bias assessment.
| Study | Year | Random sequence generation | Allocation concealment | Blinding of participants | Blinding of outcome assessment | Free of incomplete outcome | Free of selective reporting | Other bias |
|---|---|---|---|---|---|---|---|---|
| Chen et al. | 2016 | L | L | L | L | L | L | L |
| Suliburska et al. | 2012 | U | U | L | L | L | L | L |
| Mielgo-Ayuso et al. | 2014 | L | L | L | L | L | L | L |
| Hsu et al. | 2008 | L | L | L | L | L | L | L |
| Roberts et al. | 2021 | L | L | L | L | L | L | L |
| Hsu et al. | 2011 | L | L | U | U | L | L | L |
| K. Diepvens et al. | 2006 | U | U | U | U | L | L | L |
| Bajerska et al. | 2015 | U | U | U | U | L | L | U |
| Zhang et al. | 2020 | L | L | L | L | L | L | L |
| Bogdanski et al. | 2012 | L | U | U | U | L | L | L |
| Huang et al. | 2018 | L | L | L | L | L | L | U |
L, low risk of bias; H, high risk of bias; U, unclear risk of bias.
3.3. Summary of the anthropometric measurement results
Of eleven studies included，ten reported effects on BMI and waist circumference (WC), three trials reported effective green tea catechin supplementation in participants, and four trials reported effective green tea catechin intervention in reduced waist circumference. We summarized the results of all studies, and the results are shown in Fig. 2, including BMI (a) and WC(b). Green tea catechin supplementation had no significant effect on BMI in overweight and obese people (WMD = −0.38, 95 % CI: −1.13, 0.38, p = 0.326). Green tea catechin supplementation had a significant effect on waist circumference in overweight and obese people (WMD = −1.37,95 % CI: −2.52, −0.22, p = 0.019).
Fig. 2.
Forest plots (a) Funnel plot of effects of BMI (b) Funnel plot of effects of waist circumference.
3.4. Summary of blood pressure results
Of eleven studies included, nine reported effects on SBP and diastolic blood pressure, two reported green tea catechin supplementation in reducing participants, and one reported it, and we summarized all the results as shown in Fig. 2, including SBP (c) and SDP (d). The results showed that green tea catechin supplementation had no significant effect on SBP (WMD = −1.84,95 % CI: −3.81, 0.14, p = 0.069) and DBP (WMD = −1.62,95 % CI: −4.10, 0.86, p = 0.201) in overweight and obese people.
3.5. Summary of blood lipid results
Eleven reported the effects of green tea catechin supplementation on TC, TG, LDL-c, HDL-c levels. Among them 4 reported green tea catechin supplementation effectively decreased TC levels, 3 reported green tea catechin supplementation effectively reduced TG levels, 8 reported LDL-c level, and 5 reported green tea catechin supplementation effectively increased HDL-c. However, when all data from included studies were pooled for meta-analysis, The blood lipid indexes are shown in Fig. 2, which showed that he pooled results of green tea catechin supplementation on TC (WMD = −0.19, 95 % CI: −0.44, 0.06, p = 0.142), LDL-c (WMD = −0.13, 95 % CI: −0.30, −0.04，p = 0.129), in overweight and obese people, respectively, TG (WMD = −0.18, 95 % CI: −0.35, −0.02, p = 0.032) and HDL-c (WMD = 0.07, 95 % CI: 0.01, 0.14, p = 0.031) in overweight and obese people.
3.6. Summary of results of the subgroup and sensitivity analysis
Subgroup analysis of all results was performed based on the study intervention dose (>300 mg vs. ≦300 mg), intervention duration (≧12 weeks vs. <12 weeks), health status (health vs. disease), weight management (yes vs. no), and the results are shown in Table 3.Detailed information on the data is summarised in Table 4.
Table 3.
Summary results of the subgroup analysis.
| Variables | Item | Standard | No. of Trials | I2(%) | WMD (95 % CI) | P |
|---|---|---|---|---|---|---|
| SBP | dose | >300 mg | 4 | 50.3 | −2.60 (−6.18,0.99) | 0.213 |
| ≦300 mg | 4 | 27.6 | −1.50 (−3.87,0.87) | 0.156 | ||
| Duration | ≧12weeks | 7 | 0.0 | −1.04 (−3.14,1.06) | 0.332 | |
| <12weeks | 1 | – | −8.00 (−13.84,-2.16) | 0.007 | ||
| Health status | Health | 6 | 27.0 | −1.36 (−3.62,0.91) | 0.241 | |
| Disease | 2 | 65.0 | −3.36 (−7.39,0.68) | 0.103 | ||
| Weight management | Yes | 5 | 10.5 | −1.37 (−3.80,1.06) | 0.271 | |
| No | 3 | 63.8 | −2.75 (−6.15,0.64) | 0.112 | ||
| DBP | dose | >300 mg | 4 | 74.6 | −0.27 (−4.92,4.38) | 0.910 |
| ≦300 mg | 4 | 43.0 | −3.05 (−5.52,-0.59) | 0.015 | ||
| Duration | ≧12weeks | 7 | 68.5 | −0.83 (−3.64,1.97) | 0.56 | |
| <12weeks | 1 | – | −6.00 (−9.52,-2.48) | 0.001 | ||
| Health status | Health | 6 | 52.6 | −1.28 (−4.02,1.46) | 0.359 | |
| Disease | 2 | 82.1 | −1.99 (−8.87,4.88) | 0.570 | ||
| Weight management | Yes | 3 | 36.8 | −3.51 (−6.60,-0.42) | 0.026 | |
| No | 5 | 78.0 | −0.27 (−4.21,3.67) | 0.892 | ||
| TC |
dose | >300 mg | 5 | 50.2 | 0.09 (−0.15,0.33) | 0.447 |
| ≦300 mg | 5 | 43.6 | −0.46 (−0.73,-0.19) | 0.001 | ||
| Duration | ≧12weeks | 8 | 59.6 | −0.28 (−0.53,-0.04) | 0.024 | |
| <12weeks | 2 | 70.1 | 0.17 (−0.27,0.60) | 0.458 | ||
| Health status | Health | 7 | 76.5 | −0.19 (−0.50,0.11) | 0.212 | |
| Disease | 3 | 75.4 | −0.18 (−0.70,0.35) | 0.514 | ||
| Weight management |
Yes |
3 |
85.9 |
−0.04 (−0.50,0.42) |
0.871 |
|
| Variables |
Item |
Standard |
No. of Trials |
I2(%) |
WMD (95 % CI) |
P |
| TC | Weight management | No | 7 | 62.8 | −0.27 (−0.57,0.03) | 0.078 |
| TG | dose | >300 mg | 5 | 72.2 | −0.03 (−0.31,0.25) | 0.839 |
| ≦300 mg | 6 | 0.0 | −0.32 (−0.46,-0.19) | 0.000 | ||
| Duration | ≧12weeks | 9 | 60.5 | −0.20 (−0.40,-0.01) | 0.044 | |
| <12weeks | 2 | 82.1 | −0.11 (−0.53,0.30) | 0.587 | ||
| Health status | Health | 8 | 62.3 | −0.21 (−0.41,-0.01) | 0.044 | |
| Disease | 3 | 72.6 | −0.12 (−0.49，0.26) | 0.545 | ||
| Weight management | Yes | 4 | 0.0 | −0.24 (−0.40，-0.09) | 0.002 | |
| No | 7 | 75.1 | −0.15 (−0.42，0.11) | 0.251 | ||
| LDL | dose | >300 mg | 5 | 19.0 | 0.041 (−0.11，0.19) | 0.592 |
| ≦300 mg | 5 | 37.8 | −0.34 (−0.59，-0.09) | 0.008 | ||
| Duration | ≧12weeks | 8 | 47.9 | −0.18 (−0.38，0.02) | 0.071 | |
| <12weeks | 2 | 63.0 | −0.13 (−0.30，0.04) | 0.958 | ||
| Health status | Health | 7 | 56.4 | −0.12 (−0.32，0.08) | 0.257 | |
| Disease | 3 | 66.6 | −0.19 (−0.59，0.21) | 0.361 | ||
| Weight management | Yes | 3 | 63.8 | −0.03 (−0.29，0.22) | 0.804 | |
| No | 7 | 50.0 | −0.20 (−0.43，0.03) | 0.087 | ||
| HDL | dose | >300 mg | 5 | 82.3 | 0.09 (−0.05，0.23) | 0.188 |
| ≦300 mg | 6 | 0.0 | 0.06 (−0.00，0.11) | 0.052 | ||
| Duration | ≧12weeks | 9 | 0.0 | 0.03 (−0.01，0.08) | 0.131 | |
| <12weeks | 2 | 88.6 | 0.24 (−0.06，0.55) | 0.116 | ||
| Health status | Health | 8 | 72.7 | 0.08 (−0.02，0.17) | 0.107 | |
| Disease | 3 | 0.0 | 0.07 (−0.01，0.15) | 0.084 | ||
| Weight management | Yes | 4 | 85.2 | 0.12 (−0.06，0.31) | 0.186 | |
| No | 7 | 0.0 | 0.05 (−0.01，0.10) | 0.082 |
Table 4.
Data summary table.
| Study | Year | Mean of BMI (kg/m2)(CG) | SD of BMI (kg/m2)(CG | Mean of BMI (kg/m2)(IG) | SD of BMI (kg/m2)(IG) | Mean of WC (cm)(CG) | SD of WC (cm)(CG) | Mean of WC (cm)(IG) | SD of WC (cm)(IG) | Mean of SBP (mmHg)(CG) | SD of SBP (mmHg)(CG) | Mean of SBP(mmHg) (IG) |
SD of SBP(mmHg) (IG) |
Mean of DBP (mmHg)(CG) | SD of DBP (mmHg)(CG) | Mean of DBP (mmHg)(IG) | SD of DBP (mmHg)(IG) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| I-Ju Chen | 2016 | 29.1 | 3.6 | 30.6 | 3.9 | 91.5 | 8.2 | 92.8 | 9.8 | 136.2 | 18.5 | 137.0 | 16.8 | 80.6 | 11.1 | 82.2 | 13.3 |
| Joanna Suliburska | 2012 | 33.4 | 2.7 | 31.7 | 2.3 | 105.0 | 6.1 | 101.2 | 6.4 | 128.3 | 6.2 | 128.2 | 6.9 | 84.5 | 3.9 | 84.1 | 12.3 |
| Juan Mielgo-Ayuso | 2014 | 31.3 | 3.0 | 30.7 | 2.6 | 102.0 | 7.0 | 100.0 | 6.0 | NR | NR | NR | NR | NR | NR | NR | NR |
| Chung-Hua Hsu | 2008 | 30.5 | 4.6 | 31.1 | 3.7 | 91.7 | 11.5 | 93.0 | 8.5 | 132.5 | 16.9 | 131.3 | 13.5 | 79.4 | 10.9 | 81.7 | 9.1 |
| Justin D. Roberts | 2021 | 28.2 | 1.3 | 26.7 | 0.9 | 89.0 | 3.0 | 85.8 | 2.6 | 128.0 | 8.0 | 120.0 | 4.0 | 84.0 | 5.0 | 78.0 | 2.0 |
| Chung-Hua Hsu | 2011 | 29.2 | 3.3 | 30.2 | 4.3 | 94.0 | 8.4 | 96.4 | 10.3 | 142.0 | 19.1 | 146.0 | 20.6 | 85.9 | 10.2 | 88.0 | 13.5 |
| K. Diepvens | 2006 | 26.1 | 1.8 | 26.2 | 2.2 | 80.4 | 5.4 | 81.1 | 6.1 | 115.9 | 9.7 | 117.3 | 8.3 | 77.2 | 6.4 | 76.0 | 8.5 |
| Joanna Bajerska | 2015 | NR | NR | NR | NR | 104.1 | 15.0 | 103.0 | 15.1 | 134.8 | 15.5 | 132.1 | 5.0 | 86.9 | 8.4 | 84.5 | 8.8 |
| Tengfei Zhang | 2020 | NR | NR | NR | NR | NR | NR | NR | NR | NR | NR | NR | NR | NR | NR | NR | NR |
| Pawel Bogdanski | 2012 | 33.6 | 2.4 | 32.1 | 3.2 | 104.9 | 5.2 | 102.6 | 7.0 | 146.0 | 9.0 | 141.0 | 8.0 | 89.0 | 3.0 | 84.0 | 3.0 |
| Lin-Huang Huang | 2018 | 28.1 | 6.6 | 27.8 | 3.4 | 89.8 | 10.1 | 87.4 | 9.5 | NR | NR | NR | NR | NR | NR | NR | NR |
| Study | Year | Mean of TC (mmol/L)(CG) | SD of TC (mmol/L)(CG) | Mean of TC (mmol/L)(IG) | SD of TC (mmol/L)(IG) | Mean of TG (mmol/L)(CG) | SD of TG (mmol/L)(CG) | Mean of TG (mmol/L)(IG) | SD of TG (mmol/L)(IG) | Mean of LDL-c (mmol/L)(CG) | SD of LDL-c (mmol/L)(CG) | Mean of LDL-c (mmol/L)<(IG) | SD of LDL-c (mmol/L)(IG) | Mean of HDL-c (mmol/L)<(CG) | SD of HDL-c (mmol/L)(CG) | Mean of HDL-c (mmol/L) | SD of HDL-c (mmol/L)(IG) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| I-Ju Chen | 2016 | 5.02 | 1.03 | 4.75 | 0.88 | 1.78 | 1.24 | 1.49 | 0.52 | 3.08 | 0.84 | 2.90 | 0.70 | 1.21 | 0.26 | 1.21 | 0.25 |
| Joanna Suliburska | 2012 | 5.65 | 0.92 | 4.86 | 0.94 | 1.66 | 0.46 | 1.23 | 0.41 | 3.71 | 1.12 | 3.02 | 0.96 | 1.15 | 0.21 | 1.28 | 0.26 |
| Juan Mielgo-Ayuso | 2014 | 4.52 | 0.75 | 4.42 | 0.79 | 2.58 | 1.60 | 2.21 | 0.87 | 2.70 | 0.71 | 2.68 | 0.71 | 1.29 | 0.22 | 1.29 | 0.25 |
| Chung-Hua Hsu | 2008 | 5.16 | 0.83 | 5.24 | 0.86 | 1.19 | 0.38 | 1.53 | 0.88 | 3.36 | 0.84 | 3.48 | 0.82 | 1.16 | 0.29 | 1.14 | 0.26 |
| Justin D. Roberts | 2021 | 5.17 | 0.20 | 5.53 | 0.33 | 1.34 | 0.30 | 1.02 | 0.19 | 3.20 | 0.16 | 3.34 | 0.22 | 1.33 | 0.13 | 1.73 | 0.19 |
| Chung-Hua Hsu | 2011 | 5.09 | 0.92 | 5.35 | 1.08 | 2.17 | 1.31 | 2.18 | 1.27 | 3.08 | 0.62 | 3.23 | 0.85 | 0.99 | 0.31 | 1.01 | 0.23 |
| K. Diepvens | 2006 | 4.90 | 0.50 | 4.50 | 0.60 | 1.10 | 0.50 | 0.93 | 0.40 | 3.00 | 0.50 | 2.70 | 0.60 | 1.40 | 0.30 | 1.40 | 0.30 |
| Joanna Bajerska | 2015 | NR | NR | NR | NR | 1.70 | 0.60 | 1.60 | 0.90 | NR | NR | NR | NR | 1.30 | 0.20 | 1.40 | 0.30 |
| Tengfei Zhang | 2020 | 5.53 | 1.24 | 4.86 | 0.89 | 1.89 | 0.99 | 1.40 | 0.53 | 3.14 | 0.93 | 2.68 | 0.71 | 1.30 | 0.19 | 1.32 | 0.24 |
| Pawel Bogdanski | 2012 | 5.70 | 0.90 | 5.00 | 0.90 | 1.50 | 0.50 | 1.10 | 0.50 | 3.70 | 1.00 | 3.10 | 0.90 | 1.30 | 0.20 | 1.40 | 0.30 |
| Lin-Huang Huang | 2018 | 5.69 | 1.04 | 5.60 | 0.72 | 1.60 | 0.53 | 1.70 | 0.60 | 3.70 | 0.89 | 3.50 | 0.68 | 1.30 | 0.29 | 1.39 | 0.32 |
Annotation: BMI:body mass index; WC: waist circumference; NR: not report; LD: low dose; HD: high dose; TC: total cholesterol; TG: total triglyceride; HDL-c: high-density lipoprotein-cholesterol; LDL-c: low-density lipoprotein-cholesterol; CG: control group; IG: intervention group.
Sensitivity analyses were performed in primary outcomes by excluding studies with low quality or high risk of bias. All the meta-analyses results were not affected by the low quality or high risk of bias of studies (see Fig. 3).
Fig. 3.
Funnel plots (a) Sensitivity analysis of effects of BMI (b) Sensitivity analysis of effects of waist circumference.
3.7. Publication bias
According to the funnel plot (Fig. 4) and the Begg's test and Egger's tests, the results of the Begg's test were all p > 0.05 except DBP. Results with a p-value <0.05 in the Egger's test were corrected by trimming, with all corrected p-values >0.05, so that no potential publication bias was found in all the main results for BMI (Begg's test P = 0.251, Egger's test P = 0.193), WC (Begg's test P = 0.152, Egger's test P = 0.214), SBP (Begg's test P = 0.711, Egger's test P = 0.689), DBP (Begg's test P = 0.035, Egger's test P = 0.015), TC (Begg's test P = 0.283, Egger's test P = 0.061), TG (Begg's test P = 0.640, Egger's test P = 0.986), LDL-c (Begg's test P = 0.107, Egger's test P = 0.007), and HDL-c (Begg's test P = 0.161, Egger's test P = 0.247).
Fig. 4.
Sensitivity analysis.
4. Discussion
This meta-analysis involved 11 RCTs with 613 subjects. This study revealed the effect of green tea catechin supplementation on the blood pressure and lipids in overweight and obese populations. We analyzed the changes in the blood pressure (SBP, DBP) and blood lipid index (TC, TG, LDL-c, and HDL-c) in the Intervention and control groups. Meanwhile, we performed a summary analysis of BMI and WC. We found that green tea catechin supplementation effectively reduced WC, TG, and increased HDL-c levels in overweight and obese populations, but had no significant effect on other indicators.
Our meta-analysis of SBP and DBP levels showed that supplementation of green tea catechins had no significant antihypertensive effect on overweight and obese people. A meta-analysis [21] showed that there was no significant change in blood pressure in subjects with BMI >30 kg/m2, which was consistent with our study. In animal experiments, GT was able to significantly reduce blood pressure in rats. The possible mechanism is that GT significantly activated the PI3K-Akt signaling pathway, enhanced the activity of nitric oxide synthase (eNOS) and promoted the production of nitric oxide (NO), which further exerted a blood pressure-lowering effect [37]. However, other treatments or combination therapy may be needed to reduce blood pressure in obesity patients. The possible reason is that supplementation of green tea catechins alone cannot reduce the blood pressure control of green tea catechins in overweight and obese people. It is also necessary to supplement green tea catechins combined with weight management.
There are many studies on the anti-obesity effects of green tea catechin, but the results are inconsistent. This meta-analysis found that green tea catechin supplementation had no significant effect on BMI in the overweight and obese population. A meta-analysis [38] showed that healthy participants in the treatment group lost 1.31 kg compared with the control group. However, the present meta-analysis did not show the similar results due to different population. A study by Victoria [39] showed that no significant effect of green tea on BMI (SMD = −0.22, CI −0.52 to 0.074, p = 0.14) was observed with a heterogeneity of 69.7 % (p < 0.001) whereas a significant effect of green tea on body weight (SMD = −0.7, CI −1.16 to −0.23, p = 0.003) was observed with a heterogeneity of 86.4 % (p < 0.001). At the same time, a study in Korea [40], found that catechin drink intake has no significant effect on the weight in obese women, However, combining with exercise or exercise only can effectively improve the weight of obese women, which is consistent with the present study. It showed that green tea catechin supplementation in the overweight and obese population did not show significant effect on body weight.
Interestingly, this study found that green tea catechin supplementation reduced waist circumference in overweight and obese people. The possible reason to consider is that green tea catechin is able to promote fat oxidation. Therefore, the abdominal fat and the waist circumference were reduced in overweight and obese subjects. A study [41] has found that 12 weeks of green tea catechin supplementation in overweight and obese adults has significantly reduced the total abdominal fat and the subcutaneous fat area. The reduction in abdominal fat may be due to increased abdominal fat oxidation by green tea catechin supplements. Abdominal fat oxidation may lead to a decrease in TG and free fatty acid (FFA) levels.
Studies on the mechanism of green tea catechin affecting body weight have found that green tea catechin may affect the sympathetic nervous system (SNS) [42]. SNS can increase energy consumption and promote fat oxidation, resulting in weight loss. In terms of catechin increases energy consumption, there is a hypothesis about green tea catechin can inhibit catechol-o-methyl-transferase (COMT), which is the enzyme to degrade norepinephrine (NE), thus extending the prominent gap in the sympathetic system release NE. NE is the key material to make SNS activity, make the sympathetic nervous system to increase energy consumption. The hypothesis has been explored in human trials. Studies found that separate green tea catechin failed to increase energy consumption catechin [43].Catechin and caffeine work together to increase energy expenditure [44]. The mechanism of the combination of catechin and caffeine remains further study.
The results of this study showed that supplementation of green tea catechins could effectively reduce TG levels and increase HDL-c levels in overweight and obese people. However, there was no significant effect on TC and LDL-c levels in overweight and obese people. A clinical randomized controlled trial showed that EGCG supplementation significantly reduced fasting plasma TG levels after 8 weeks of green tea catechin supplementation in obese people (p < 0.05) [16]. The results were consistent with this study, indicating that EGCG significantly reduced TG levels in overweight and obese people. There are some possible mechanisms to explain how EGCG reduces TG levels. A study in rats [45] showed that tea-catechin dose-dependently inhibited pancreatic lipase activity, thereby inhibiting triglyceride absorption and postprandial hypertriglyceridemia. In addition, green tea catechins have been shown to increase cholesterol 7α-hydroxylase gene expression in HepG2 cells [46,47] which may stimulate bile acid production and reduce cholesterol levels in hepatocytes [48]. Another study [22] on rat hepatoma cells showed that EGCG reduced the assembly and secretion of apoB-100 ultra-low density lipoprotein (VLDL) and reduced TG levels. The decrease of TG level is beneficial to the blood lipid of overweight and obese people.
More studies have found that supplementation of green tea can reduce LDL-c. A meta-analysis [49] showed that supplementation with green tea reduced TC and LDL-c levels in subjects. Another study [50] discussed the role of EGCG in reducing LDL-c. Studies have shown that EGCG in the form of beverages or capsules significantly reduces LDL-C levels in non-drug-treated healthy subjects. This is different from the results of this study. The reason for the different results may be that the research objects are different. The subjects of this study were overweight and obese people. It may be that the supplementation of green tea catechins has a more obvious effect on increasing HDL-c in overweight and obese people.
The results of subgroup analysis showed that DBP, TC, TG and LDL were significantly decreased when the dose of green tea catechin was ≦ 300 mg. Supplementation of green tea catechin time <12 weeks, SBP, DBP decreased significantly. When the time of green tea catechin supplementation ≧ 12 weeks, TC and TG indexes decreased significantly. Supplementation of green tea catechins while weight management, DBP, TG index decreased significantly. The results of subgroup analysis showed that the dose of green tea catechin should be controlled within 300 mg per day in overweight and obese people. Short-term supplementation of green tea catechins has a certain effect on blood pressure in overweight and obese people. Long-term supplementation of green tea catechins has a certain effect on blood lipid indexes of overweight and obese people. Supplementation of green tea catechins combined with weight management can effectively reduce blood pressure and blood lipid indicators.
The limitations of this study are self-evident. First, a smaller sample size in the included studies may lead to a higher risk of publication bias. This review shows that DBP has publication bias according to publication bias detection. The possible reason is that the number of research objects included in this paper is not enough. Secondly, this study did not conduct a subgroup analysis of gender because of insufficient sample size. However, in our study, due to different sex ratios, different hormone levels have different effects on obesity, blood pressure and lipids. Finally, we failed to find the exact source of heterogeneity in blood pressure and lipid parameters through subgroup analysis and meta-analysis.
5. Conclusion
In overweight and obese people, green tea catechin supplementation has a certain effect on lipid spectrum, which can effectively reduce the waist circumference in overweight and obese people, reduce TG and HDL-c in elevated blood lipid. However, it has no significant effect on BMI, SDP, DBP, TC, and LDL-c levels. This meta-analysis showed a moderate benefit of green tea catechin supplementation on lipid profiles in overweight and obese people, especially in reducing the function of both TG levels and elevated HDL-c levels.
Funding statement
We appreciate that the support from the National Natural Science Foundation of China (NO. 82003457), Jiangsu Province Science Foundation for Youths (NO. BK20200366), the Fundamental Research Funds for the Central Universities and “Zhishan” Scholars Programs of Southeast University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Author Contributions Statement
Ying Wang: Conceived and designed the experiments; Acquired of data; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper. Hui Xia: Conceived and designed the experiments；Analyzed and interpreted the data; Revised the article. Junhui Yu and Jing Sui: Analyzed and interpreted the data Da Pan, Shaokang Wang and Wang Liao,: Contributed reagents, materials, analysis tools or data. Ligang Yang and Guiju Sun: Conceived and designed the experiments. All authors have approved the manuscript.
Data Availability Statement
Declaration of Interest Statement All data generated or analysed during this study are included in this published article and its supplementary information files.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Footnotes
Supplementary data to this article can be found online at https://doi.org/10.1016/j.heliyon.2023.e21228.
Appendix A. Supplementary data
The following is the Supplementary data to this article.
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Data Availability Statement
Declaration of Interest Statement All data generated or analysed during this study are included in this published article and its supplementary information files.