Health effects of green tea catechins in overweight and obese men: a randomised controlled cross-over trial

British Journal of Nutrition
Q1
Jun 2011
Citations:138
Influential Citations:7
Interventional (Human) Studies
84
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Methods
Single-centre, placebo-controlled, double-blind, randomized cross-over trial in sedentary overweight/obese men aged 40–69 years (BMI 28–38 kg/m2) with no significant disease. Two 6-week treatment periods (active DGT and placebo) in random order, with a washout between periods. Measurements included ambulatory blood pressure and fasting metabolic biomarkers; COMT rs4680 genotype analysis; 24 h urine collections and dietary/activity diaries.
Intervention
Decaffeinated green tea extract (DGT), 530 mg per capsule, taken two capsules daily (total ~1060 mg/day), containing >75% catechins and <1% caffeine; taken 1 hour before breakfast and 1 hour before the evening meal, for 6 weeks per treatment period.
Results
DGT increased plasma EGCG to about 98 ng/mL and markedly increased urinary excretion of EGC and 4′-O-methyl EGC (roughly 28-fold and 34-fold), confirming absorption. No effect on 24 h ambulatory blood pressure, heart rate, or fasting metabolic biomarkers. A period-by-treatment interaction suggested a possible weight-protective effect during intervention period 1 (DGT −0.64 kg vs placebo +0.53 kg; P = 0.025); in period 2 weight changes were similar (DGT −0.32 kg; placebo −0.55 kg). COMT Val/Met genotype influenced urinary EGC and 4′-O-methyl EGC excretion, with lower levels in GG homozygotes. No robust genotype-by-treatment interactions were detected for weight or other outcomes. Conclusion: six weeks of daily DGT was well tolerated but did not lower blood pressure or improve metabolic biomarkers; potential weight-management effect under energy imbalance and genotype-related differences in catechin metabolism warrant further study.
Limitations
Small sample size; cross-over design with potential order effects; short duration (6 weeks per period); predominantly normotensive population; potential seasonal influences on weight; multiple secondary outcomes increasing risk of type I error; limited power to detect genotype interactions.

Abstract

Regular consumption of green tea may be cardioprotective. In the present study we investigated the health effects of dietary supplementation with green tea catechins and the potential modifying effect of the catechol-O-methyltransferase (COMT) Val/Me...