Green tea benefits?

Antioxidants, such as the polyphenols found in green tea, have been championed for their value in cancer protection. Their role in eye disease prevention, however, is still unclear. Dorairajan Balasubramanian, director of research, L.V. Prasad Eye Institute, Hyderabad, India, reported on in vitro tests he has performed on cells and polyphenols such as epigallocatechin gallate (ECGC) and catechin, and their protective value against cytotoxic agents.

“These are very powerful antioxidants. They penetrate the cell membrane and protect the cells from DNA damage," Dr Balasubramanian said. "We looked at their protective value in cataract formation, but lens replacement is basically so simple now that the real question has become: Are the polyphenols in tea good for glaucoma?”

To find out, Dr Balasubramanian examined retinal ganglion cells and stressed them using hydrogen peroxide. He found that while various polyphenols did offer a protective effect to the retinal cells, some potentially brought their toxicity to the table.

“For example, both catechin and EGCG protect the cells, but there is a toxicity to retinal cells associated with EGCG that isn't associated with catechin,” Dr Balasubramanian said. He found the same protective-yet-toxic qualities in resveratrol, the antioxidant of red wine fame.

Other unanswered questions remain: Solubility in water. Does the systemically taken green tea molecule reach the eye? “Do you need to drink green tea for 40 years for this to have an effect, or could eye drops provide a boost?” Dr Balasubramanian asked. “What’s the best mode to reach the proper concentration? That’s an interesting question that still needs to be answered.”

What is the optimum dose for human eye protection? Does the preparation of the tea itself affect the protective qualities of the antioxidants? Dr Balasubramanian said that the sun drying of oolong tea changes the catechin on a molecular level, and the heat treatment of black tea gives it its characteristic colour and flavour but adds molecules in the process.

“Is that good? We don't know,” he said. “Should we all be drinking green tea as they do here in Hong Kong, or black tea as we do in India?”