Researchers from the Chinese University of Hong Kong report that catechins from tea could be detected in significant amounts in various eye structures. According to findings published in the Journal of Agricultural and Food Chemistry, the retina of rats absorbed the highest levels of gallocatechin, while the aqueous humor tended to absorb epigallocatechin.
Furthermore, the potential beneficial effects of green tea catechins in reducing harmful oxidative stress were sustained for up to 20 hours.
Eyes on the market
A report from Frost & Sullivan last year stated that the global market for eye health ingredients was dominated by antioxidants, including lutein, beta-carotene, zeaxanthin, astaxanthin and bilberry.
The demand for such products is increasing as consumers turn to nutrition to protect against blinding diseases such as age-related macular degeneration and glaucoma.
The global human nutrition market for lutein is predicted to reach $125m within three years, said F&S, with growth underpinned by rising demand for eye health supplements from the aging US population, increasing healthcare costs, more research efforts backing ingredient benefits, and improvements in technology for methods of ingredient extraction, said the report.
“Although many antioxidants have been studied in the eye, to the best of our knowledge this is the first paper to show distribution of individual catechins after ingestion of green tea extract and to evaluate their in vivo antioxidative effects in various parts of the mammalian eye,” wrote t he researchers behind the new study.
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.
Study details
Chi Pui Pang and colleagues fed laboratory rats green tea and subsequently analysed the eye tissues. Catechins were indeed observed in the eye tissues, say the researchers.
“Many studies on the antioxidative effect of green tea focused on EGCG,” report the researchers. “However, in this study, we found its tissue level was not high. Gallocatechin, epigallocatechin, catechin, and epicatechin, on the other hand, substained high levels in many compartments.
“Although these compounds have a reducing power similar to or lower than that of EGCG, use of a mixture, such as green tea extract, was better than use of a single catechin because of lower cost and synergic effects on antioxidation and bioavailability,” they added.
“Our results indicate that green tea consumption could benefit the eye against oxidative stress,” concluded the researchers.
The green tea extracts, Sunphenon DCF-1, were donated by Taiyo Kagaku Co. Ltd.
Source: Journal of Agricultural and Food Chemistry
Volume 58, Issue 3, Pages 1523–1534, doi: 10.1021/jf9032602
“Green Tea Catechins and Their Oxidative Protection in the Rat Eye”
Authors: K.O. Chu, K.P. Chan, C.C. Wang, C.Y. Chu, W.Y. Li, K.W. Choy, M.S. Rogers, C.P. Pang