Table 1. Characteristics of 13 randomized controlled trials included in analysis.
| Source | No. of subjects | Study design | Population | Duration | Tea group | Control group | Jadad score | Type of dieta |
|---|---|---|---|---|---|---|---|---|
| Fukino, 2005, Japan (11) | 66 | Parallel | Stage 1 hypertension, overweight, 32–73 y of age | 2 mo | DGTB (544 mg polyphenols) | No tea | <4 | Usual diet |
| Diepvens, 2006, Netherlands (12) | 46 | Parallel | Prehypertension, overweight, 19–57 y of age | 87 d | GTE capsule (1,207 mg polyphenols, 236.7 mg caffeine) | Placebo (maltodextrin capsule) | <4 | Low-energy diet |
| Nagao, 2007, Japan (13) | 240 | Parallel | Prehypertension, obese, 25–55 y of age | 12 wk | GTE beverage (582.8 mg polyphenols, 72.3 mg caffeine) | GTE beverage (96 mg catechins, 75.0 mg caffeine) | <4 | Usual diet |
| Hill, 2007, Switzerland (14) | 38 | Parallel | Prehypertension, overweight/obese, 45–70 y of age | 12 wk | DGTE capsule (300 mg polyphenols) | Placebo (lactose capsules) | <4 | Usual diet with excise |
| Fukino, 2008, Japan (15) | 70 | Crossover | Stage 1 hypertension, overweight, 32–73 y of age | 2 mo | GTE beverage (544 mg polyphenols, 102 mg caffeine) | Water | <4 | Usual diet |
| Nagao, 2009, Japan (16) | 43 | Parallel | Prehypertension, T2DM, 64.9 ± 1.6 y of age | 12 wk | GTE beverage (582.8 mg polyphenols, 72.3 mg caffeine) | GTE beverage (96.3 mg catechins, 75.0 mg caffeine) | <4 | Usual diet |
| Frank, 2009, UK (17) | 33 | Parallel | Prehypertension, overweight,18–55 y of age | 3 wk | GTE Capsule (714 mg polyphenols, 114 mg caffeine) | Placebo (maltodextrin) | <4 | Usual diet |
| Brown, 2009, UK (18) | 88 | Parallel | Prehypertension, overweight/obese, 40–65 y of age | 8 wk | DGTE capsule (800 mg polyphenols) | Placebo (lactose capsules) | ≥4 | Usual diet |
| Nantz, 2009, USA (19) | 111 | Parallel | Prehypertension, overweight, 21–70 y of age | 3 mo | DGTB (320 mg polyphenols) | Placebo capsule | ≥4 | Usual diet |
| Basu, 2010, USA (20) | 22 | Parallel | BP < 160/100 mmHg, obesity and metabolic syndrome, 25–63 y of age | 8 wk | Green tea beverage (928 mg polyphenols, 8.96 mg caffeine) | Water | <4 | Usual diet |
| Brown, 2011, UK (21) | 66 | Crossover | Prehypertension, overweight and obese, 40–69 y of age | 6 wk | DGTE capsule (800 mg polyphenols) | Placebo (lactose capsules) | ≥4 | Usual diet |
| Suliburska, 2012, Poland (22) | 46 | Parallel | Prehypertension, obese, 30–60 y of age | 3 mo | DGTE capsule (208 mg polyphenols) | Placebo capsules (cellulose) | ≥4 | Usual diet |
| Bogdanski, 2012, Poland (23) | 56 | Parallel | Stage 1 hypertension, obese, 30–60 y of age | 3 mo | DGTE capsule (208 mg polyphenols) | Placebo capsules (cellulose) | ≥4 | Usual diet |
Abbreviations: DGTB, Decaffeinated green tea beverage; DGTE, decaffeinated green tea extract; EGCG, epigallocatechin gallat; GTE, green tea extract; T2DM, type 2 diabetes mellitus.
aA usual diet was similar to a conventional diet; a low-energy diet contained less amounts of energy than a usual diet.