"EGCG acutely improves endothelial function in humans with coronary artery disease, and may account for a portion of the beneficial effects of flavonoid-rich food on endothelial function," wrote the authors in the Journal of the American College of Nutrition .
European demand for tea extracts is currently surging, and this has seen companies such as DSM, with its Teavigo boasting 95 per cent purity of EGCG, and Taiyo International, with its Sunphenon claiming more than 90 per cent purity, position themselves firmly in specific catechin markets.
The researchers, led by Michael Widlansky from Boston University School of Medicine in collaboration with researchers from DSM Nutritional Products, state that epidemiological studies have demonstrated the benefits of dietary flavonoid intake.
These may be related to improved endothelial function.
Widlansky and co-workers recruited 42 subjects to take part in the double blind, placebo-controlled, crossover design study.
Subjects were randomly assigned to receive either an EGCG supplement or a placebo.
Blood flow in the arm, so-called brachial artery flow-mediated dilation (FMD), was measured by vascular ultrasound at baseline, and again after two hours after an initial dose of EGCG (300 mg) or placebo, and after two weeks of supplementation with EGCG (two 150 mg doses per day) or placebo.
Before being crossed-over to the other intervention, the subjects underwent a one-week washout period.
Supplementation with the green tea extract was found to improve FMD from 7.1 to 8.6 per cent two hours after the initial 300 milligram dose, but was not significantly improved when measurements were taken 14 hours after the end of the two weeks of supplementation.
Blood levels of EGCG mirrored the vascular function, said the researchers, increasing from 2.6 to 92.8 nanograms per millilitre after the initial 300 mg dose, but returning approximately to baseline levels after two weeks (3.4 ng/ml).
The results add to an ever-growing body of science linking consumption to a wide range of health benefits, including lower risk of certain cancers, increased weight loss, improved heart health, and protection against Alzheimer's.
Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent.
The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.
Source: Journal of the American College of Nutrition Volume 26, Number 2, Pages 95-102 "Acute EGCG Supplementation Reverses Endothelial Dysfunction in Patients with Coronary Artery Disease" Authors: M.E. Widlansky, N.M. Hamburg, E. Anter, M. Holbrook, D.F. Kahn, J.G. Elliott, J.F. Keaney, Jr., and J.A. Vita