European Journal of Nutrition

, Volume 53, Issue 6, pp 1299–1311 | Cite as

Green tea catechins and blood pressure: a systematic review and meta-analysis of randomised controlled trials

  • Saman Khalesi
  • Jing Sun
  • Nicholas Buys
  • Arash Jamshidi
  • Elham Nikbakht-Nasrabadi
  • Hossein Khosravi-Boroujeni
Review

Abstract

Purpose

Although previous literature has reported that regular green tea consumption may improve blood pressure, the evidence from these studies is not consistent. The present study systematically reviewed randomised controlled trials and examined the effect of green tea consumption on blood pressure using meta-analysis.

Methods

Search of ProQuest, PubMed, Scopus and Cochrane Library (CENTERAL) was conducted, to identify eligible articles. Articles from 1995 to 2013 were included. A random-effect model was chosen to calculate the effect of combined trials.

Result

Thirteen studies were included in the meta-analysis. Green tea consumption significantly changed systolic blood pressure, by −2.08 mm Hg (95 % CI −3.06, −1.05), and diastolic blood pressure, by −1.71 mm Hg (95 % CI −2.86, −0.56), compared to the control. Changes in lipid profile, blood glucose and body mass index were also assessed in the meta-analysis. A significant reduction was found in total cholesterol (−0.15 mmol/L [95 % CI −0.27, −0.02]) and low-density lipoprotein cholesterol (−0.16 mmol/L [95 % CI −0.22, −0.09]). Changes in other parameters did not reach statistical significance. Subgroup analysis suggested a greater reduction in both systolic and diastolic blood pressure in studies that included participants with a baseline mean systolic blood pressure of ≥130 mm Hg, and studies involving consuming green tea as an extract.

Conclusion

The present meta-analysis suggests that green tea and its catechins may improve blood pressure, and the effect may be greater in those with systolic blood pressure ≥130 mm Hg. The meta-analysis also suggests that green tea catechins may improve total and low-density lipoprotein cholesterol.

Keywords

Green tea Blood Pressure Lipid profile Systematic review Meta-analysis 

Introduction

Hypertension is one of the most common diseases in the world, leading to major health complications such as cardiovascular disease, strokes and renal and kidney dysfunction [1]. A significant prevalence of high blood pressure (BP) among adults 25 years and older exists, with a worldwide incidence rate of 40 % [2]. It is also estimated that hypertension is a comorbid factor in 69 % of people who have their first heart attack and 75 % of those with chronic heart failure [3]. A 5 mm Hg reduction in BP can reduce the risk of stroke and ischaemic heart disease by 34 and 21 %, respectively [4, 5].

Diet plays an important role in the treatment and control of high BP [6]. Recently, there has been a focus on the role that substances such as flavonoids can play in treatment and control of high BP [7]. Green tea (GT) is made from the steamed and dried leaves of the Camellia sinensis plant. It is a widely consumed beverage containing healthy phenolic components (flavonoids), which have anti-oxidative effects on the body [8]. Specific flavonoids known as flavan-3-ols, or catechins, constitute up to 35 % of the dry weight of GT [8]. A cup of non-fermented GT contains more than 80 % flavonoids, compared to black tea with only 20–30 % flavonoids [9, 10]. Numerous studies have been published on GT and its health benefits on lipid profile [11], blood glucose levels [12], cancer [13, 14], hypertension [15, 16] and weight reduction [16, 17]. This study conducted a systematic review and meta-analysis of controlled trials to clarify the effect of GT on BP. These findings can provide guidance on interventions at both clinical and population health levels.

Methods

Study strategy

Relevant articles on GT and BP were located through electronic databases, including ProQuest, PubMed, Scopus and Cochrane Library (CENTERAL). Included articles ranged from January 1995 to 2013 and were considered recent studies on GT and BP. Search terms are listed in Table S1. The results are reported in accordance with the guidelines provided in the “Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA)” statement [18]. Database searching, scanning and screening of articles were conducted independently by two authors using the same set of eligibility criteria, detailed below. A third author was involved in decision-making regarding inclusion or exclusion, in cases where consensus could not be reached between the original reviewers.

Eligibility criteria

For studies to be included in the systematic review, they had to meet the following inclusion criteria:
  • The study design must have been a randomised controlled trial (RCT), using a parallel design examining GT consumption in a human population over at least a 4-week period. GT consumption is defined as consuming liquid GT or its extract or supplements.

  • Participants must have been adults aged 18 years or older, with or without hypertension, diabetes or vascular disease.

  • Publications must be in English, with full studies, not just abstracts.

Exclusion was based on the following factors:
  • if studies examined only the short-term or postprandial effects of GT on BP

  • if consumption involved extraction from sources other than GT, such as artificial catechins, or involved mixtures of GT with other substances

  • if studies failed to address or describe the dose, frequency and intervention period of GT consumption

  • if they failed to report BP as an outcome measurement in studies examining the effect of GT on metabolic syndrome, obesity or body weight.

Measurement of outcomes

Changes in systolic BP (SBP) and diastolic BP (DPB) from baseline were measured as primary outcomes of this review. As secondary outcomes, changes in total cholesterol (TC), high- and low-density lipoproteins (HDL-C and LDL-C), triglycerides (TG), glucose level and body mass index (BMI) were collected. Dose dependency of the effect of GT and effective methods of GT consumption were assessed further (the process is explained in the data synthesis and subgroup analysis section).

Selecting included studies

Two experienced researchers conducted an initial screening of studies based on title and evidence of use of a human population. The next phase involved a review of the abstract and an examination of the full text in terms of the inclusion criteria. The final decision on eligible articles was made by two reviewers, if an agreement was reached, and three in the case of disagreement between the first two. A summary of the review is presented in the PRISMA flow chart [19] in Figure S1.

Methodology quality assessment

The methodological quality of eligible articles was assessed using Downs and Black’s 32-item quality checklist [20]. The checklist studies’ power was calculated and compared with small, medium and large power values (0.20, 0.50 and 0.80, respectively) described by Cohen et al. [21]. Studies with methodology quality scores >12 of the total score were considered good quality and included in the study [22].

Data extraction

All included articles were reviewed by two assessors to extract all relevant data, following the “checklist of items to consider in data collection” from the Cochrane handbook for systematic review of interventions [23, 24]. Based on this checklist, information on study method and design, participants, results, side effects, author comments and eligibility of study were extracted from studies. For those articles published from one study, only one article was chosen and included, although duplicates were also reviewed for any important information.

Data synthesis, sensitivity and subgroup analysis

Data were analysed using Review Manager Software (RevMan, version 5.2.6, Cochrane Collaboration). Data were expressed by mean difference of baseline and end point. Statistical analysis was performed following the guidelines in the Cochrane handbook [23, 24]. The effect model considered for the meta-analysis was the DerSimonian and Laird random effect [25]. Due to high heterogeneity in BP analysis, and variation between studies’ populations, the random-effect model was considered. A p value <0.05 was considered significant.

Sensitivity analysis was limited to interventions reporting improvement in both SBP and DBP. The effect of each study on the overall results of meta-analysis was also investigated. In addition, sensitivity was limited to studies that reported significant reduction of body weight or BMI, to assess the possible influence of weight loss on meta-analysis results of BP. Subgroup and sensitivity analyses were performed to assess how studies with different methodologies affected overall weight of effects, following the methods described by Kim et al. [26] and Dong et al. [27]. Studies using liquid GT were compared to those using GT extract. Studies including subjects with a baseline SBP ≥ 130 mm Hg were compared to those in which participants had a baseline SBP of <130 mm Hg. Studies including dietary modification in addition to GT were also considered another subgroup. The dose dependency relationship of the effect of GT on BP was assessed by re-arranging the meta-analysis plot of BP based on high- to low-dose GT catechins. To further investigate the effect of dose of GT catechins, a subgroup analysis of GT trials with daily catechins consumption of ≥500 mg was also compared to those with daily catechins consumption of <500 mg.

Results

Characteristics of included articles

Fourteen RCTs using a parallel design investigating the effect of GT on BP were included in the systematic review and meta-analysis. The methodology quality score of included articles is presented in Table S2. All studies were rated as good quality, based on Downs and Black’s checklist. One study had the lowest score of 24 [28], and two studies had the highest score of 29 [29, 30].

Characteristics of the included articles and their effect size (based on the DerSimonian and Laird random effect) are presented in Table 1. Of the 13 studies included, all reported both SBP and DBP changes (n = 1,040). Eleven studies reported fasting lipid profile measures [16, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38] and changes in TC. Ten studies measured LDL changes [16, 28, 29, 31, 33, 34, 35, 36, 37, 38]; nine studies reported changes in HDL-C [16, 28, 29, 31, 32, 33, 34, 37, 38]; and 10 studies measured changes in TG [16, 28, 29, 31, 32, 33, 34, 35, 37, 38]. Ten studies also reported changes in fasting glucose levels [16, 28, 29, 30, 31, 32, 33, 34, 35, 37] and the same number presented changes in BMI [16, 28, 30, 31, 32, 33, 34, 35, 37, 38, 39]. Six studies were focused on obese individuals [16, 28, 34, 35, 37, 39]; two on diabetic individuals [33, 35]; and one on people with hypertension [31]. The duration of studies varied from 3 weeks [32] to 4 months [33], and the mean age of participants varied from 28.9 ± 7.9 [36] to 60–80 years old [38]. Nine studies included both males and females, one included only males [32] and three only females [30, 34, 39]. In five studies, consumption of GT was in liquid form [16, 28, 29, 35, 38], with the remaining studies using capsules of GT extract [30, 31, 32, 33, 34, 36, 37, 39]. Dose of GT varied from three commercial tea bags a day, to three capsules containing 375 mg catechins in each, or six capsules of 384 mg GT extract (see Table 1). Of the 13 studies included, two mentioned that they measured nutrient and dietary intake of participants at baseline and after the intervention [16, 28]. Two studies mentioned that participants were prohibited from catechin-rich foods before participation or were instructed to limit their catechins intake [16, 32]. One study indicated the exclusion of those who consumed more than 259 ml of tea per day, seven or more servings of fruit and vegetables per day, or took supplements [36]. The remaining studies reported that participants were instructed to maintain their previous eating habits [16, 29, 30, 31, 33, 34, 37, 39].
Table 1

Characteristics of included articles

Study (year)

Duration of study

Participants No. in intervention/control (dropout rate), intervention mean age, mean BMI, country

Disease, condition

Green tea type, (daily dose) vs. placebo

Intervention outcomes, mean (SD) before/after SBP, DBP (mm Hg) TC, TG, LDL, HDL (mmol/L) GLU (mmol/L) BMI (kg/m2)

Control outcomes, mean (SD) before/after SBP, DBP (mm Hg) TC, TG, LDL, HDL (mmol/L) GLU (mmol/L) BMI (kg/m2)

Effect size on SBP

Basu et al. [29]

8 weeks

28/28 (0 %), 42.5 ± 1.7 years, 36.1 ± 1.3 kg/m2, male and female, USA

Metabolic syndrome

Liquid, tea bags (440 mg EGCG) versus water

SBP: 132.0 ± 3.5/127.6 ± 3.1

DBP: 83.0 ± 2.2/80.1 ± 2.5

TC: 5.0 ± 0.3/4.9 ± 0.2

TG: 1.9 ± 0.3/2.0 ± 0.3

LDL: 3.16 ± 0.26/2.98 ± 0.23

HDL: 1.04 ± 0.05/1.01 ± 0.03

GLU: 5.0 ± 0.2/4.9 ± 0.2

SBP:130.0 ± 2.6/127.3 ± 2.6

DBP: 80.0 ± 2.1/80.3 ± 2.6

TC: 5.48 ± 0.27/5.43 ± 0.23

TG: 1.5 ± 0.2/1.6 ± 0.3

LDL: 3.73 ± 0.24/3.71 ± 0.18

HDL: 1.08 ± 0.05/1.11 ± 0.02

GLU: 4.9 ± 0.2/4.8 ± 0.2

0.579

Bogdanski et al. [31]

3 months

28/28 (0 %), 49.2 ± 8.8 years, male and female, Poland

Hypertensive

Extract (379 mg GT, 208 mg EGCG) versus pure cellulose

SBP: 145 ± 10/141 ± 8

DBP: 88 ± 4/84 ± 3

BMI: 32.5 ± 3.3/32.1 ± 3.2

TC: 5.4 ± 1.0/5.0 ± 0.9

TG: 1.4 ± 0.6/1.1 ± 0.5

LDL: 3.5 ± 1.0/3.1 ± 0.9

HDL: 1.2 ± 0.2/1.4 ± 0.3

GLU: 5.5 ± 0.4/5.3 ± 0.3

SBP: 146 ± 10/146 ± 9

DBP: 89 ± 3/89 ± 3

BMI: 33.9 ± 2.3/33.6 ± 2.4

TC: 5.6 ± 1.1/5.7 ± 0.9

TG: 1.5 ± 0.6/1.5 ± 0.5

LDL: 3.7 ± 1.2/3.7 ± 1.0

HDL: 1.2 ± 0.2/1.3 ± 0.2

GLU: 5.6 ± 0.5/5.5 ± 0.4

0.463

Diepvens et al. [42]

87 days

23/23 (0 %), 41.6 ± 10.0 years, 27.7 ± 1.8 kg/m2, female, Netherlands

Overweight, normotensive

Diet + extract (1,125 mg catechins) versus extract (250 mg catechins)

SBP: 127.4 ± 11.8/117.3 ± 8.3

DBP: 80.0 ± 12.0/76.0 ± 8.5

BMI: 27.7 ± 1.8/26.2 ± 2.2

SBP: 122.5 ± 13.2/115.9 ± 9.7

DBP: 78.6 ± 8.9/77.2 ± 6.4

BMI: 27.7 ± 1.8/26.1 ± 1.8

0.370

Frank et al. [32]

3 weeks

16/16 (5.8 %), 50.5 ± 9.2 years, male, UK

Healthy

Extract (2,304 mg GT, 714 mg polyphenol) versus maltodextrin

SBP: 125 ± 10/123 ± 10

DBP: 78 ± 8/79 ± 8

BMI: 26.7 ± 3.3/26.7 ± 3.3

TC: 4.09 ± 1.09/3.97 ± 0.77

TG: 1.11 ± 0.66/1.04 ± 0.58

HDL: 0.88 ± 0.31/0.92 ± 0.27

GLU: 3.86 ± 0.86/3.92 ± 0.65

SBP: 126 ± 16/125 ± 17

DBP: 79 ± 11/77 ± 9

BMI: 25.4 ± 3.4/25.2 ± 3.2

TC: 3.79 ± 1.50/3.85 ± 1.23

TG: 0.97 ± 0.44/1.04 ± 0.64

HDL: 0.99 ± 0.35/0.99 ± 0.27

GLU: 3.82 ± 1.1/3.99 ± 0.91

0.209

Fukino et al. [30]

2 month

33/33(0 %), 53.5 ± 8.5 years, 27.7 ± 1.8 kg/m2, female, Netherlands

Fasting blood glucose ≥ 6.1 mmol/L or non-fasting level ≥ 7.7 mmol/L

Extract and power (9:1) (456 mg catechins) versus no supplement

SBP: 139.3 ± 15.7/131.6 ± 20.8

DBP: 92.5 ± 11.1/83.3 ± 12.6

BMI: 25.5 ± 4.8/25.2 ± 4.5

GLU: 7.49 ± 3.29/7.14 ± 2.58

SBP: 138.6 ± 18.2/129.2 ± 19.0

DBP: 87.8 ± 11.5/83.2 ± 15.3

BMI: 25.9 ± 3.9/25.8 ± 3.9

GLU: 7.78 ± 2.64/7.20 ± 1.62

0.085

Hsu et al. [34]

12 weeks

37/41 (26 %), 43.0 ± 11.1 years, female, Taiwan

Obese

Extract (1,200 mg GT, 491 mg catechins) versus placebo cellulose

SBP: 134.9 ± 16.2/131.2 ± 13.5

DBP: 82.9 ± 9.3/81.7 ± 9.1

BMI: 31.2 ± 3.5/31.1 ± 3.7

TC: 5.47 ± 0.92/5.24 ± 0.85

TG: 3.66 ± 2.11/3.51 ± 2.02

LDL: 3.90 ± 0.86/3.48 ± 0.82

HDL: 1.10 ± 0.24/1.14 ± 0.25

GLU: 6.27 ± 2.09/6.24 ± 1.88

SBP: 135.4 ± 20.0/135.2 ± 16.9

DBP: 81.6 ± 11.5/79.4 ± 10.9

BMI: 30.5 ± 4.6/30.5 ± 4.6

TC: 5.24 ± 0.85/5.17 ± 0.82

TG: 3.57 ± 2.28/2.73 ± 0.86

LDL: 3.50 ± 0.92/3.36 ± 0.84

HDL: 1.16 ± 0.28/1.15 ± 0.29

GLU: 5.77 ± 1.44/5.92 ± 1.7

0.251

Hsu et al. [33]

16 weeks

35/33 (12.5 %), 50.5 ± 9.2 years, male and female, Taiwan

Type 2 diabetes

Extract (1,500 mg GT, 856.8 mg EGCG) versus cellulose

SBP: 147 ± 20.6/146 ± 20.6

DBP: 88.6 ± 12.7/88.0 ± 13.5

BMI: 30.2 ± 4.3/30.2 ± 4.3

TC: 5.4 ± 1.00/5.35 ± 1.08

TG: 2.14 ± 1.41/2.18 ± 1.27

LDL: 3.36 ± 0.86/3.23 ± 0.85

HDL: 1.01 ± 0.23/1.01 ± 0.23

GLU: 9.52 ± 3.36/8.76 ± 2.99

SBP: 150 ± 17.6/142 ± 19.1

DBP: 87.6 ± 2.7/85.9 ± 10.2

BMI: 29.2 ± 3.6/29.2 ± 3.3

TC: 5.31 ± 0.73/5.09 ± 0.92

TG: 3.57 ± 2.28/2.17 ± 1.31

LDL: 3.07 ± 0.81/3.08 ± 0.62

HDL: 0.97 ± 0.24/0.99 ± 0.31

GLU: 9.71 ± 3.23/9.17 ± 3.27

0.447

Nagao et al. [35]

12 weeks

123/117 (9 %), 41.7 ± 9.9 years, male and female, Japan

Visceral fat-type obese,

Beverage (583 mg catechins) versus beverage (96 mg catechins)

SBP: 127 ± 14.8/124.3 ± 14.2

DBP: 76.9 ± 10.4/75.8 ± 9.1

BMI: 26.9 ± 1.9/26.2 ± 1.9

TC: 5.58 ± 0.99/5.38 ± 0.98

TG: 1.94 ± 1.03/1.99 ± 1.21

LDL: 3.41 ± 0.86/3.31 ± 0.89

HDL: 1.42 ± 0.37/1.36 ± 0.33

GLU: 5.43 ± 1.37/5.32 ± 1.20

SBP: 128.8 ± 14.3/128.8 ± 15.1

DBP: 77.9 ± 9.2/77.1 ± 10.1

BMI: 26.7 ± 2.1/26.6 ± 2.2

TC: 5.44 ± 0.94/5.31 ± 0.97

TG: 1.82 ± 1.07/1.68 ± 0.89

LDL: 3.34 ± 0.82/3.38 ± 0.86

HDL: 1.39 ± 0.33/1.36 ± 0.32

GLU: 5.17 ± 1.48/5.19 ± 1.45

0.183

Nagao et al. [36]

12 weeks

23/20 (8 %), 64.9 ± 1.6 years, male and female, Japan

Type 2 Diabetes

Beverage (582.8 mg catechins) versus beverage (96.3 mg catechins)

SBP: 138.0 ± 2.6/132.0 ± 3.1

DBP: 78.2 ± 1.8/75.2 ± 1.5

BMI: 25.6 ± 0.8/25.5 ± 0.7

TC: 5.55 ± 0.13/5.38 ± 0.14

TG: 1.44 ± 0.16/1.25 ± 0.11

GLU: 7.44 ± 0.31/7.00 ± 0.24

SBP: 135.0 ± 3.1/131.1 ± 3.2

DBP: 76.9 ± 2.5/76.0 ± 2.1

BMI: 24.0 ± 0.9/24.0 ± 1.0

TC: 5.29 ± 0.15/5.42 ± 0.20

TG: 1.55 ± 0.29/1.55 ± 0.28

GLU: 7.22 ± 0.26/7.49 ± 0.37

0.655

Nantz et al. [37]

3 month

55/56 (9 %), 28.9 ± 7.95 years, male and female, USA

Healthy

Extract (400 mg catechins) versus cellulose

SBP: 131 ± 6.3/128 ± 6.3

DBP: 80 ± 4.2/79 ± 4.2

TC: 4.61 ± 0.32/4.53 ± 0.32

LDL: 2.54 ± 0.3/2.47 ± 0.3

SBP: 129 ± 6.0/129 ± 6.0

DBP: 78 ± 3.7/80 ± 3.7

TC: 4.55 ± 0.32/4.55 ± 0.32

LDL: 2.53 ± 0.28/2.61 ± 0.3

0.484

Sone et al. [28]

9 weeks

29/26 (0 %), 43.2 ± 14.8 years, male and female, Japan

Overweigh and obese

Beverage (400 mg catechins), versus beverage (100 mg catechins

SBP: 123 ± 15/123 ± 19

DBP: 75 ± 10/74 ± 12

BMI: 24.6 ± 4.3/24.0 ± 4.1

TC: 4.66 ± 0.82/4.75 ± 0.77

TG: 1.20 ± 1.15/1.14 ± 1.06

LDL: 2.7 ± 0.68/2.76 ± 0.73

HDL: 1.37 ± 0.36/1.42 ± 0.37

GLU: 5.3 ± 0.68/5.34 ± 0.75

SBP: 123 ± 16/123 ± 13

DBP: 76 ± 10/76 ± 10

BMI: 24.5 ± 4.2/24.1 ± 3.9

TC: 4.96 ± 0.67/4.93 ± 0.7

TG: 1.31 ± 1.63/0.93 ± 0.47

LDL: 2.98 ± 0.75/2.97 ± 0.75

HDL: 1.46 ± 0.37/1.47 ± 0.37

GLU: 5.48 ± 0.53/5.35 ± 0.45

0.000

Suliburska et al. [38]

3 month

23/23 (0 %), 48.56 ± 8.81 years, male and female, Poland

Obese

Extract (379 mg GT, 208 mg EGCG) versus cellulose

SBP: 130.72 ± 6.95/128.15 ± 6.86

DBP: 85.10 ± 12.47/84.06 ± 12.26

BMI: 32.07 ± 2.41/31.71 ± 2.29

TC: 5.22 ± 0.97/4.86 ± 0.94

TG: 1.46 ± 0.49/1.23 ± 0.41

LDL: 3.44 ± 1.03/3.02 ± 0.96

HDL: 1.12 ± 0.24/1.28 ± 0.26

GLU: 5.64 ± 0.44/5.48 ± 0.31

SBP: 129.58 ± 7.88/128.32 ± 6.16

DBP: 84.21 ± 3.32/84.50 ± 3.86

BMI: 33.45 ± 2.65/33.36 ± 2.66

TC: 5.62 ± 1.05/5.62 ± 0.92

TG: 1.6 ± 0.42/1.66 ± 0.46

LDL: 3.80 ± 1.19/3.71 ± 1.12

HDL: 1.09 ± 0.25/1.15 ± 0.21

GLU: 5.67 ± 0.44/5.59 ± 0.43

0.197

Vieira Senger et al. [39]

60 days

24/21 (0 %), 60–80 years, male and female, Brazil

Elderly metabolic syndrome

Liquid, tea bag 3 time a day, versus Control

SBP: 126.7 ± 12.7/123.7 ± 9.7

DBP: 76.2 ± 9.2/73.3 ± 6.3

BMI: 30.5 ± 4.3/30.0 ± 4.4

TC: 11.1 ± 3.1/10.8 ± 1.9

TG: 10.1 ± 3.7/10.2 ± 3.7

LDL: 6.5 ± 3.1/6.1 ± 2.2

HDL: 2.5 ± 0.4/2.4 ± 0.5

GLU: 6.8 ± 2.6/6.6 ± 1.7

SBP: 137.6 ± 11.8/132.9 ± 9.0

DBP: 82.9 ± 12.7/76.2 ± 7.4

BMI: 30.4 ± 4.5/30.2 ± 4.6

TC: 10.8 ± 1.9/10.0 ± 1.7

TG: 8.4 ± 2.7/7.7 ± 2.9

LDL: 6.6 ± 1.6/5.9 ± 1.5

HDL: 2.6 ± 0.6/2.5 ± 0.8

GLU: 6.4 ± 1.1/6.5 ± 1.3

0.240

EGCG epigallocatechin gallate, SBP systolic blood pressure, DBP diastolic blood pressure, TC total cholesterol, TG triglyceride, LDL low-density lipoprotein, HDL high-density lipoprotein, GLU glucose, GT green tea, BMI body mass index

Of the 13 studies included, 11 reported a reduction in both SBP and DBP [16, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39]. Three studies reported a reduction of 6–10 mm Hg for SBP after GT consumption [30, 35, 39], and five reported reduction of 3–4 mm Hg for SBP [29, 31, 34, 36, 38]. Five studies also showed a reduction of 3–10 mm Hg for DBP after GT consumption [30, 31, 35, 36, 39].

Meta-analysis results

Forest plot results of changes in BP, lipid profile, glucose level and BMI are presented in Figs. 1, 2 and 3. Overall, consumption of GT was associated with significant changes of SBP, a mean difference of −2.05 mm Hg (95 % CI −3.06, −1.05), compared to control groups. Mean difference of DBP also changed significantly, by −1.71 mm Hg (95 % CI −2.86, −0.56) after GT consumption compared to control groups. GT consumption significantly changed TC (mean difference −0.15 mmol/L [95 % CI −0.27, −0.02]) and LDL-C (mean difference −0.16 mmol/L [95 % CI −0.2, −0.09]) but did not significantly change the mean differences of TG or HDL-C. Changes in BMI and fasting blood glucose also did not reach statistical significance. Statistical heterogeneity was not observed in the analysis of SBP, BMI and LDL-C (I2 = 0 %). The lowest level of statistical heterogeneity occurred with HDL-C (I2 = 49 %). Analysis of DBP, TC, TG and blood glucose showed moderate to high levels of heterogeneity (I2 = 52, 55, 80 and 81 % respectively).
Fig. 1

Forest plots of the studies investigating the effect of GT on mean difference of SBP (mm Hg) (a), DBP (mm Hg) (b). Data are presented as mean with 95 % CI. Plots are created using the Review Manager Software (RevMan version 5.2.6)

Fig. 2

Forest plots of the studies investigating the effect of GT on mean difference of TC (mmol/L) (a); TG (mmol/L) (b); LDL-C (mmol/L) (c); and HDL-C (mmol/L) (d). Data are presented as mean with 95 % CI. Plots are created using the Review Manager Software (RevMan version 5.2.6)

Fig. 3

Forest plots of the studies investigating the effect of GT on mean difference of glucose (mmol/L) (a) and BMI (kg/m2) (b). Data are presented as mean with 95 % CI. Plots are created using the Review Manager Software (RevMan version 5.2.6)

Sensitivity and subgroup analysis results

The sensitivity analysis showed that limiting studies to those reporting improvement in both SBP and DBP only slightly affected the mean difference of SBP and DBP (see Table 2). Sensitivity analysis of individual studies also did not affect the overall significance of the mean effect on SBP or DBP. Limiting meta-analysis to the four studies reporting significant reduction in body weight and BMI [16, 28, 38, 39] also did not meaningfully affect the mean difference of SBP or DBP. Results of the subgroup analysis are presented in Table 2. Subgroup analysis of GT extract compared with GT liquid resulted in greater reduction in SBP (−2.44 vs. −1.79 mm Hg) and DBP (−2.24 vs. −1.10 mm Hg). Consumption of GT in studies where the mean baseline SBP of the intervention group was ≥130 mm Hg showed significant reduction in both SBP and DBP. Subgroup analysis of studies with participants’ mean baseline SBP < 130 mm Hg did not indicate significant reduction of SBP or DBP compared to the control groups. GT consumption did not change BP significantly compared to the control in subgroup analysis of trials, including participants with a mean baseline BMI of ≥30 kg/m2. However, the subgroup analysis of studies that included participants with a mean baseline BMI of <30 kg/m2 resulted in a significant reduction of both SBP and DBP compared with control groups. Mean differences of SBP and DBP among studies that used GT intervention without dietary modification were also significantly lower than in the control groups.
Table 2

Results of sensitivity analysis of included randomised controlled trials in meta-analysis of GT on BP

Sensitivity analysis

Weight mean difference (95 % confidence interval)

Number of trials

SBP (mm Hg)

DBP (mm Hg)

Improvement in both SBP and DBP

−2.09 (−3.11, −1.08; ρ < 0.05)

−1.91 (−3.08, −0.75; ρ < 0.05)

12

Significant reduction in BW or BMI

−1.72 (−4.26, 0.81; ρ = 0.18)

0.09 (−2.43, 2.61; ρ = 0.94)

4

Subgroup analysis

   

GT as beverage

−1.79 (−3.09, −0.49; ρ < 0.05)

−1.10 (−2.96, 0.76; ρ = 0.25)

5

GT as extract

−2.44 (−4.02, −0.98; ρ < 0.05)

−2.24 (−3.77, −0.71; ρ < 0.05)

8

Catechins dose ≥ 500 mg/day

−2.30 (−3.87, −0.74; ρ < 0.05)

−1.33 (−2.92, 0.25; ρ = 0.10)

4

Catechins dose < 500 mg/day

−2.67 (−4.73, −0.61; ρ < 0.05)

−2.37 (−4.15, −0.58; ρ < 0.05)

4

Without dietary modification

−2.00 (−3.02, −0.98; ρ < 0.05)

−1.62 (−2.84, −0.41; ρ < 0.05)

12

Mean baseline SBP ≥ 130 mm Hg

−2.13 (−3.23, −1.03; ρ < 0.05)

−2.69 (−3.59, −1.78; ρ < 0.05)

8

Mean baseline DBP < 130 mm Hg

−1.68 (−4.13, 0.78; ρ = 0.18)

0.44 (−1.81, 2.69; ρ = 0.70)

5

Mean baseline BMI ≥ 30 kg/m2

−1.39 (−3.33, 0.59; ρ = 0.16)

−0.98 (−3.47, 1.50; ρ = 0.44)

6

Mean baseline BMI < 30 kg/m2

−2.40 (−3.67, −1.13; ρ < 0.05)

−2.03 (−3.03, −1.03; ρ < 0.05)

7

All trials (meta-analysis result)

−2.05 (−3.06, −1.05; ρ < 0.05)

−2.26 (−2.91, −1.62; ρ < 0.05)

13

GT green tea, SBP systolic blood pressure, DBP diastolic blood pressure

All interventions, except the study by Vieira Senger et al. [38], reported the dose of either catechins or epigallocatechin-3-gallate (EGCG, the major catechins content of GT). Of these studies, eight reported the total daily intake of catechins [16, 28, 30, 32, 33, 35, 36, 39]. The highest daily dose was reported by Diepvens et al. [39], with 1125 mg, and the lowest was reported by Sone et al. [28]. Five studies did not report the total daily dose of GT-derived catechins [29, 31, 33, 37, 38] and were not included in dose dependency analysis. Dose dependency of the effect of GT catechins on BP was assessed by re-arranging the Forest plot based on the dose of catechins (from high to low dose). The re-arranged Forest plot did not show any meaningful trend between the daily dose of GT catechins consumption and the mean difference of SBP and DBP (see Figure S2). However, the subgroup analysis of trials indicated slightly better reduction in SBP and DBP in trials with daily catechins consumption of GT < 500 mg, compared to those with daily catechins consumption ≥500 mg (Table 2).

Discussion

All included articles were rated as good quality in relation to Downs and Black’s quality checklist [20]. Generally, papers received a lower score through several factors: not stating whether participants experienced adverse effects [30, 32, 35, 37, 38, 39]; the study treatment environment or participants did not represent the entire population of interest [28, 29, 31, 34, 39]; the actual probability value for main outcomes was not reported [16, 30, 32, 35, 36, 37, 40]; or blinding was not followed or reported [30, 38].

The results of this systematic review showed that consumption of GT and its catechins can significantly reduce mean difference of SBP and DBP (−2.05, −1.71 mm Hg, respectively). Although the reduction in BP reported in this meta-analysis is small, even a slight reduction of BP at population level can have important clinical and public health-related outcomes. The results of a published overview showed that 2 mm Hg reduction in DBP can result in a 17 % lower prevalence of hypertension, a 6 % lower risk of chronic heart disease (CHD) and a 15 % reduction in the risk of stroke [41]. Green tea catechins may have vasodilatory properties, through increasing plasma nitric oxide concentration [42, 43]. Nitric oxide can also reduce the plasma level of pro-inflammatory cytokines, reduce the platelet aggregation and improve endothelium function [43]. Increased levels of serum endothelin-1 (ET-1) may also induce endothelial dysfunction, as ET-1 is a potent vasoconstrictor [44]. GT catechins may reduce the serum level of ET-1 [45]. The actions of GT catechins in reducing ET-1 and increasing NO may lead to relaxation on vascular tone and BP [42].

This meta-analysis also showed that the effect of GT on BP is greater when baseline SBP is equal or more than 130 mm Hg (pre-hypertension and hypertension stage). The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure (JNC7) mentioned that dietary modifications—including a reduction of fat and salt intake and an increase in fruit and vegetable intake—can reduce BP and improve hypertension status [6]. The present study also shows that adding GT to the daily diet can improve BP, providing an additional guideline to dietary modification for hypertension. Weight loss may greatly affect BP changes [6]. However, the sensitivity analysis indicates that limiting analysis to studies reported a significant reduction in body weight did not result in a meaningful reduction in BP. This finding may be due to the low number of studies included in sensitivity analysis (four trials) or may indicate that the meta-analysis effect reported for BP is not affected by body weight changes. In addition, findings from the subgroup analysis of studies with baseline participants’ BMI of ≥30 kg/m2 did not indicate significant changes in BP. These findings suggest that GT catechins may not effectively improve BP in obese individuals; other therapies or combinations of therapies may be necessary to lower BP in such individuals.

The subgroup analysis also indicates that GT extract may have a greater benefit on BP than other forms. The preparation or storage of liquid GT may result in catechins loss [50], or the difference may be due to the lower number of studies using GT liquid: five studies did so [16, 28, 29, 35, 38], in contrast to eight that used GT extract [30, 31, 32, 33, 34, 36, 37, 39].

This meta-analysis also found significant improvements in TC and LDL-C after consuming GT. Catechins have antioxidant and anti-inflammatory properties [46]. Several studies have shown that GT and its catechins may reduce cholesterol [47, 48, 49]. The exact mechanism of this action is not yet established; however, inhibition of intestinal cholesterol absorption [48, 50], cholesterol biosynthesis [49] and increase in faecal excretion [51] of fatty acid are proposed mechanisms for such effects of GT catechins. GT catechins may have fat-burning properties [52] by inhibiting catechol O-methyltransferase, which may increase the concentration of norepinephrine, consequently increasing thermogenesis and fat metabolism [53]. GT catechins may also inhibit hydroxy-3-methyl-glutaryl-CoA reductase, which is a mediating enzyme in cholesterol synthesis [42, 53]. Catechins may form insoluble binds with cholesterol in the intestine and inhibit the absorption of cholesterol [48].

The re-arranged Forest plot for dose dependency of the effect of GT on SBP or DBP did not show any meaningful relationships. However, the reduction in SBP and DBP was slightly better in trials consuming daily GT catechins <500 mg. In addition, Sone et al. [28] reported no significant improvement of SBP or DBP by consuming a daily dose of 400 mg GT catechins. The low number of studies in each subgroup may affect these results. However, due to the caffeine content of GT (around 25 mg caffeine per 100 ml) [54], it may be possible that high GT consumption increases the norepinephrine secretion and raises BP [55]. These findings may suggest that daily consumption of GT with a dose of 400–500 mg catechins is most beneficial for lowering BP. Based on a study by Henning et al. [54], commercial GT bags may have a catechins content of around 153 mg per bag (1.5–2.4 g). Therefore, three servings of GT bags may provide enough catechins to affect BP beneficially. Further studies with differing doses of GT consumption would need to be conducted in order to confirm this finding.

To date, many studies have examined the effect of GT on BP and lipid profile. Some of these had small sample sizes, such as Frank et al. [32], with 16 participants in the intervention group. Others had larger sample sizes, such as Nagao et al. [16] with 123 participants. The strength of the current meta-analysis was its capacity to increase sample size, and the statistical power of the analysis to reflect more robust and generalisable results. In addition, it included only RCTs, considered optimal for analysing intervention effects and reducing the impact of confounding factors. However, a limitation of this meta-analysis was that secondary measures were only included if primary measures of BP were examined in the study. Therefore, if changes in BP were not examined or reported in studies that evaluated changes in lipid profile, blood glucose or body weight, such studies were not included in meta-analysis. Moreover, some studies included in the present meta-analysis did not report whether the randomisation was blind, or did not explain the blinding and randomisation process [30, 38]. The duration of most of the interventions was short, with relatively small sample sizes of 23–35 participants in each group [28, 29, 31, 32, 33, 37, 38, 39]. Further, some studies included participants with baseline high BP [29, 31, 33] or other complications such as diabetes [30, 33, 35, 56], whereas others included only healthy adults [32, 36]. Except for two studies that reported no significant difference in the dietary intake of the intervention and control groups [16, 28], others did not control the effects that changing dietary habits could have on their findings. Because of these limitations, the translation of the present meta-analysis results to a population health level should only be undertaken cautiously.

Conclusion

GT is an inexpensive and common drink. The present meta-analysis of the literature suggests that consumption of GT and its catechins may improve BP. The study also suggests GT consumption has a beneficial effect on TC, LDL-C and glucose levels. Further studies are required with large samples size over a longer duration to confirm the effect of different methods of GT consumption on BP, lipid profiles and glucose levels among populations with different chronic conditions.

Notes

Conflict of interest

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Supplementary material

394_2014_720_MOESM1_ESM.docx (44 kb)
Supplementary material 1 (DOCX 43 kb)
394_2014_720_MOESM2_ESM.docx (30 kb)
Supplementary material 2 (DOCX 29 kb)
394_2014_720_MOESM3_ESM.docx (15 kb)
Supplementary material 3 (DOCX 14 kb)
394_2014_720_MOESM4_ESM.docx (17 kb)
Supplementary material 4 (DOCX 16 kb)

References

  1. 1.
    WHO (2002) World Health Organization. World Health Report 2002. Reducing risks, promoting healthy life. Geneva, Switzerland. http://wwww.hoint/whr/2002/en
  2. 2.
    WHO (2008) Global health observatory (GHO). Raised blood pressure. http://www.who.int/gho/ncd/risk_factors/blood_pressure_prevalence_text/en/index.html
  3. 3.
    Roger VL, Go AS, Lloyd-Jones DM, Benjamin EJ, Berry JD, Borden WB, Bravata DM, Dai S, Ford ES, Fox CS (2012) Heart disease and stroke statistics—2012 update a report from the American Heart Association. Circulation 125(1):e2–e220CrossRefGoogle Scholar
  4. 4.
    Law M, Wald N, Morris J (2005) Lowering blood pressure to prevent myocardial infarction and stroke: a new preventive strategy. Int J Technol Assess Health Care 21(1):145. doi:10.1017/s0266462305220196 Google Scholar
  5. 5.
    Qureshi A, Sapkota B (2011) Blood pressure reduction in secondary stroke prevention. Continuum (Minneapolis, Minn) 17 (6 2ndary Stroke Prevention):1233Google Scholar
  6. 6.
    Chobanian AV, Bakris GL, Black HR, Cushman WC, Green LA, Izzo JL, Jones DW, Materson BJ, Oparil S, Wright JT (2003) Seventh report of the joint national committee on prevention, detection, evaluation, and treatment of high blood pressure. Hypertension 42(6):1206–1252CrossRefGoogle Scholar
  7. 7.
    Hooper L, Kroon PA, Rimm EB, Cohn JS, Harvey I, Le Cornu KA, Ryder JJ, Hall WL, Cassidy A (2008) Flavonoids, flavonoid-rich foods, and cardiovascular risk: a meta-analysis of randomized controlled trials. Am J Clin Nutr 88(1):38–50Google Scholar
  8. 8.
    Rains TM, Agarwal S, Maki KC (2011) Antiobesity effects of green tea catechins: a mechanistic review. J Nutr Biochem 22(1):1–7CrossRefGoogle Scholar
  9. 9.
    Balentine DA, Wiseman SA, Bouwens LC (1997) The chemistry of tea flavonoids. Crit Rev Food Sci Nutr 37(8):693–704CrossRefGoogle Scholar
  10. 10.
    Bhardwaj P, Khanna D (2013) Green tea catechins: defensive role in cardiovascular disorders. Chin J Nat Med 11(4):345–353Google Scholar
  11. 11.
    Erba D, Riso P, Bordoni A, Foti P, Biagi PL, Testolin G (2005) Effectiveness of moderate green tea consumption on antioxidative status and plasma lipid profile in humans. J Nutr Biochem 16(3):144–149. doi:10.1016/j.jnutbio.2004.11.006 CrossRefGoogle Scholar
  12. 12.
    Maruyama K, Iso H, Sasaki S, Fukino Y (2009) The association between concentrations of green tea and blood glucose levels. J Clin Biochem Nutr 44(1):41CrossRefGoogle Scholar
  13. 13.
    Mu LN, Lu QY, Yu SZ, Jiang QW, Cao W, You NC, Setiawan VW, Zhou XF, Ding BG, Wang RH (2005) Green tea drinking and multigenetic index on the risk of stomach cancer in a Chinese population. Int J Cancer 116(6):972–983CrossRefGoogle Scholar
  14. 14.
    Sun C-L, Yuan J-M, Koh W-P, Mimi CY (2006) Green tea, black tea and breast cancer risk: a meta-analysis of epidemiological studies. Carcinogenesis 27(7):1310–1315CrossRefGoogle Scholar
  15. 15.
    Antonello M, Montemurro D, Bolognesi M, Di Pascoli M, Piva A, Grego F, Sticchi D, Giuliani L, Garbisa S, Rossi GP (2007) Prevention of hypertension, cardiovascular damage and endothelial dysfunction with green tea extracts. Am J Hypertens 20(12):1321–1328CrossRefGoogle Scholar
  16. 16.
    Nagao T, Hase T, Tokimitsu I (2007) A green tea extract high in catechins reduces body fat and cardiovascular risks in humans. Obesity 15(6):1473–1483. doi:10.1038/oby.2007.176 CrossRefGoogle Scholar
  17. 17.
    Auvichayapat P, Prapochanung M, Tunkamnerdthai O, Sripanidkulchai B-O, Auvichayapat N, Thinkhamrop B, Kunhasura S, Wongpratoom S, Sinawat S, Hongprapas P (2008) Effectiveness of green tea on weight reduction in obese Thais: a randomized, controlled trial. Physiol Behav 93(3):486–491CrossRefGoogle Scholar
  18. 18.
    Moher D, Liberati A, Tetzlaff J, Altman DG (2009) Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. Ann Intern Med 151(4):264–269CrossRefGoogle Scholar
  19. 19.
    Liberati A, Moher D, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JPA, Clarke M, Devereaux PJ, Kleijnen J (2009) The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration. PLoS Med 6(7):e1000100. doi:10.1371/journal.pmed.1000100 CrossRefGoogle Scholar
  20. 20.
    Downs SH, Black N (1998) The feasibility of creating a checklist for the assessment of the methodological quality both of randomised and non-randomised studies of health care interventions. J Epidemiol Commun Health 52(6):377–384CrossRefGoogle Scholar
  21. 21.
    Cohen J (1992) A power primer. Psychol Bull 112(1):155–159. doi:10.1037/0033-2909.112.1.155 CrossRefGoogle Scholar
  22. 22.
    Harrison RA, Siminoski K, Vethanayagam D, Majumdar SR (2007) Osteoporosis-related kyphosis and impairments in pulmonary function: a systematic review. J Bone Miner Res 22(3):447–457CrossRefGoogle Scholar
  23. 23.
    Higgins J, Green SP, Wiley I, Cochrane C (2008) Cochrane handbook for systematic reviews of interventions. vol Book, Whole. Wiley-Blackwell, HobokenCrossRefGoogle Scholar
  24. 24.
    Higgins J, Green S (2011) Cochrane handbook for systematic reviews of interventions version 5.1.0 [updated March 2011]. The Cochrane Collaboration, Medical Research Council, UKGoogle Scholar
  25. 25.
    DerSimonian R, Laird N (1986) Meta-analysis in clinical trials. Control Clin Trials 7(3):177–188. doi:10.1016/0197-2456(86)90046-2 CrossRefGoogle Scholar
  26. 26.
    Kim A, Chiu A, Barone MK, Avino D, Wang F, Coleman CI, Phung OJ (2011) Green tea catechins decrease total and low-density lipoprotein cholesterol: a systematic review and meta-analysis. J Am Diet Assoc 111(11):1720–1729CrossRefGoogle Scholar
  27. 27.
    Dong J-Y, Szeto IM, Makinen K, Gao Q, Wang J, Qin L-Q, Zhao Y (2013) Effect of probiotic fermented milk on blood pressure: a meta-analysis of randomised controlled trials. Br J Nutr 110(07):1188–1194CrossRefGoogle Scholar
  28. 28.
    Sone T, Kuriyama S, Nakaya N, Hozawa A, Shimazu T, Nomura K, Rikimaru S, Tsuji I (2011) Randomized controlled trial for an effect of catechin-enriched green tea consumption on adiponectin and cardiovascular disease risk factors. Food Nutr Res 55:1–10. doi:10.3402/fnr.v55i0.8326 CrossRefGoogle Scholar
  29. 29.
    Basu A, Du M, Sanchez K, Leyva MJ, Betts NM, Blevins S, Wu M, Aston CE, Lyons TJ (2011) Green tea minimally affects biomarkers of inflammation in obese subjects with metabolic syndrome. Nutrition 27(2):206–213. doi:10.1016/j.nut.2010.01.015 CrossRefGoogle Scholar
  30. 30.
    Fukino Y, Shimbo M, Aoki N, Okubo T, Iso H (2005) Randomized controlled trial for an effect of green tea consumption on insulin resistance and inflammation markers. J Nutr Sci Vitaminol (Tokyo) 51(5):335–342CrossRefGoogle Scholar
  31. 31.
    Bogdanski P, Suliburska J, Szulinska M, Stepien M, Pupek-Musialik D, Jablecka A (2012) Green tea extract reduces blood pressure, inflammatory biomarkers, and oxidative stress and improves parameters associated with insulin resistance in obese, hypertensive patients. Nutr Res 32(6):421–427. doi:10.1016/j.nutres.2012.05.007 CrossRefGoogle Scholar
  32. 32.
    Frank J, George TW, Lodge JK, Rodriguez-Mateos AM, Spencer JP, Minihane AM, Rimbach G (2009) Daily consumption of an aqueous green tea extract supplement does not impair liver function or alter cardiovascular disease risk biomarkers in healthy men. J Nutr 139(1):58–62. doi:10.3945/jn.108.096412 CrossRefGoogle Scholar
  33. 33.
    Hsu CH, Liao YL, Lin SC, Tsai TH, Huang CJ, Chou P (2011) Does supplementation with green tea extract improve insulin resistance in obese type 2 diabetics? A randomized, double-blind, and placebo-controlled clinical trial. Altern Med Rev 16(2):157–163CrossRefGoogle Scholar
  34. 34.
    Hsu CH, Tsai TH, Kao YH, Hwang KC, Tseng TY, Chou P (2008) Effect of green tea extract on obese women: a randomized, double-blind, placebo-controlled clinical trial. Clin Nutr 27(3):363–370CrossRefGoogle Scholar
  35. 35.
    Nagao T, Hase T, Tokimitsu I (2007) A green tea extract high in catechins reduces body fat and cardiovascular risks in humans. Obesity (Silver Spring) 15(6):1473–1483. doi:10.1038/oby.2007.176 CrossRefGoogle Scholar
  36. 36.
    Nantz MP, Rowe CA, Bukowski JF, Percival SS (2009) Standardized capsule of Camellia sinensis lowers cardiovascular risk factors in a randomized, double-blind, placebo-controlled study. Nutrition 25(2):147–154CrossRefGoogle Scholar
  37. 37.
    Suliburska J, Bogdanski P, Szulinska M, Stepien M, Pupek-Musialik D, Jablecka A (2012) Effects of green tea supplementation on elements, total antioxidants, lipids, and glucose values in the serum of obese patients. Biol Trace Elem Res 149(3):315–322. doi:10.1007/s12011-012-9448-z CrossRefGoogle Scholar
  38. 38.
    Vieira Senger AE, Schwanke CHA, Gomes I, Valle Gottlieb MG (2012) Effect of green tea (Camellia sinensis) consumption on the components of metabolic syndrome in elderly. J Nutr Health Aging 16(9):738–742. doi:10.1007/s12603-012-0081-5 CrossRefGoogle Scholar
  39. 39.
    Diepvens K, Kovacs EM, Nijs IM, Vogels N, Westerterp-Plantenga MS (2005) Effect of green tea on resting energy expenditure and substrate oxidation during weight loss in overweight females. Br J Nutr 94(6):1026–1034CrossRefGoogle Scholar
  40. 40.
    Chantre P, Lairon D (2002) Recent findings of green tea extract AR25 (exolise) and its activity for the treatment of obesity. Phytomedicine 9(1):3–8CrossRefGoogle Scholar
  41. 41.
    Cook NR, Cohen J, Hebert PR, Taylor JO, Hennekens CH (1995) Implications of small reductions in diastolic blood pressure for primary prevention. Arch Intern Med 155(7):701–709. doi:10.1001/archinte.1995.00430070053006 CrossRefGoogle Scholar
  42. 42.
    Islam MA (2012) Cardiovascular effects of green tea catechins: progress and promise. Recent Pat Cardiovasc Drug Discov 7(2):88–99CrossRefGoogle Scholar
  43. 43.
    Rastaldo R, Pagliaro P, Cappello S, Penna C, Mancardi D, Westerhof N, Losano G (2007) Nitric oxide and cardiac function. Life Sci 81(10):779–793CrossRefGoogle Scholar
  44. 44.
    Gössl M, Lerman A (2006) Endothelin beyond a vasoconstrictor. Circulation 113(9):1156–1158CrossRefGoogle Scholar
  45. 45.
    Collins QF, Liu H-Y, Pi J, Liu Z, Quon MJ, Cao W (2007) Epigallocatechin-3-gallate (EGCG), a green tea polyphenol, suppresses hepatic gluconeogenesis through 5′-AMP-activated protein kinase. J Biol Chem 282(41):30143–30149CrossRefGoogle Scholar
  46. 46.
    Pon Anandh B, Dongmin L (2008) Green tea catechins and cardiovascular health: an update. Curr Med Chem 15(18):1840–1850. doi:10.2174/092986708785132979 CrossRefGoogle Scholar
  47. 47.
    Maron DJ, Lu GP, Cai NS, Wu ZG, Li YH, Chen H, Zhu JQ, Jin XJ, Wouters BC, Zhao J (2003) Cholesterol-lowering effect of a theaflavin-enriched green tea extract: a randomized controlled trial. Arch Intern Med 163(12):1448–1453CrossRefGoogle Scholar
  48. 48.
    Koo SI, Noh SK (2007) Green tea as inhibitor of the intestinal absorption of lipids: potential mechanism for its lipid-lowering effect. J Nutr Biochem 18(3):179–183CrossRefGoogle Scholar
  49. 49.
    Bursill CA, Abbey M, Roach PD (2007) A green tea extract lowers plasma cholesterol by inhibiting cholesterol synthesis and upregulating the LDL receptor in the cholesterol-fed rabbit. Atherosclerosis 193(1):86–93CrossRefGoogle Scholar
  50. 50.
    Ikeda I, Kobayashi M, Hamada T, Tsuda K, Goto H, Imaizumi K, Nozawa A, Sugimoto A, Kakuda T (2003) Heat-epimerized tea catechins rich in gallocatechin gallate and catechin gallate are more effective to inhibit cholesterol absorption than tea catechins rich in epigallocatechin gallate and epicatechin gallate. J Agric Food Chem 51(25):7303–7307CrossRefGoogle Scholar
  51. 51.
    Hsu T, Kusumoto A, Abe K, Hosoda K, Kiso Y, Wang M, Yamamoto S (2006) Polyphenol-enriched oolong tea increases fecal lipid excretion. Eur J Clin Nutr 60(11):1330–1336CrossRefGoogle Scholar
  52. 52.
    Westerterp-Plantenga MS (2010) Green tea catechins, caffeine and body-weight regulation. Physiol Behav 100(1):42–46CrossRefGoogle Scholar
  53. 53.
    Rains TM, Agarwal S, Maki KC (2011) Antiobesity effects of green tea catechins: a mechanistic review. J Nutr Biochem 22(1):1–7CrossRefGoogle Scholar
  54. 54.
    Henning SM, Fajardo-Lira C, Lee HW, Youssefian AA, Go VL, Heber D (2003) Catechin content of 18 teas and a green tea extract supplement correlates with the antioxidant capacity. Nutr Cancer 45(2):226–235CrossRefGoogle Scholar
  55. 55.
    Noordzij M, Uiterwaal CS, Arends LR, Kok FJ, Grobbee DE, Geleijnse JM (2005) Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials. J Hypertens 23(5):921–928CrossRefGoogle Scholar
  56. 56.
    Barter P, Gotto AM, LaRosa JC, Maroni J, Szarek M, Grundy SM, Kastelein JJP, Bittner V, Fruchart J-C, Treating New Targets I, Treating to New Targets I (2007) HDL cholesterol, very low levels of LDL cholesterol, and cardiovascular events. N Engl J Med 357(13):1301–1310. doi:10.1056/NEJMoa064278 CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Saman Khalesi
    • 1
  • Jing Sun
    • 1
    • 2
  • Nicholas Buys
    • 1
  • Arash Jamshidi
    • 3
    • 4
  • Elham Nikbakht-Nasrabadi
    • 1
  • Hossein Khosravi-Boroujeni
    • 1
  1. 1.Griffith Health InstituteGriffith UniversityGold CoastAustralia
  2. 2.School of MedicineGriffith UniversityGold CoastAustralia
  3. 3.Nephrology and UrologySina General HospitalTehranIran
  4. 4.Supplementary Medicine DepartmentSondos Teb CoTehranIran

Personalised recommendations