Study Finds Green Tea Could Reduce Glaucoma Risk
Lee Swanson Research Update
The study results were published in the Journal of Agricultural and Food Chemistry and indicate that green tea consumption could benefit the eye against oxidative stress.
Scientists analyzed eye tissue from rats that drank green tea and found that the lens, retina and other tissues absorbed significant amounts of green tea catechins.
Although many studies have been done on antioxidants and eye health, the authors claim that theirs 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 eye.
The authors said that oxidative stress causes biological disturbances such as DNA damage and activation of proteolytic enzymes that can lead to tissue cell damage or dysfunction and eventually many ophthalmic diseases.
"Photooxidative stress can inactivate catalase in the lens to initiate cataract formation, while long-term effects of reactive oxygen intermediates could damage retinal tissue cells, retinal pigment epithelium and choriocapillaries. Oxidation is also associated with primary open angle glaucoma (POAG)," they said.
Green tea contains between 30% and 40% of water-extractable polyphenols, and the four primary polyphenols found in fresh tea leaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC).
In the study, green tea extract (GTE) in tablet form was suspended in 0.5 ml of water, the authors said. A dosage of 550 mg/kg of GTE was fed to rats and the authors added that the doses of catechins were comparable to most published reports: 178 mg/kg EGCG, 82.7 mg/kg ECG, 80.7 mg/kg gallocatechin gallate (GCG), 72.0 mg/kg EC, 58.7 mg/kg EGC, 56.7 mg/kg gallocatechin (GC) and 24 mg/kg catechin (C).
The researchers said the rats were sacrificed at different time intervals and the eyes of the animals were then dissected for cornea, lens, retina, choroids-sclera, vitreous humor and aqueous humor tissues.
Analysis of eye tissues demonstrated that eye structures absorbed significant amounts of individual catechins, the researchers said. The time of maximum concentration of the catechins varied from 30 minutes to around 12 hours.
The authors found that catechins were differentially distributed in eye tissues—the retina absorbed the highest levels of gallocatechin, while the aqueous humor tended to absorb epigallocatechin.
Significant reductions in 8-epi-isoprostane levels were found in the compartments except the choroids-sclera or plasma, indicating antioxidative activities of catechins in these tissues, the team concluded.
Journal of Agricultural and Food Chemistry Published online ahead of print.
May 2010