Wednesday March 10, 2010 | 1 comment
By now, it’s not news to anyone that green tea is at the top of our Super Foods list. Over the past 10 years or so there have been myriad research studies showing that tea has very powerful anti-oxidative effects that provide significant health benefits for numerous organs and systems throughout the body. Recently, a new study was done that brought to light potential benefits to yet another important organ of the body – our eyes.
A recent study, conducted by Kai On Chu et al – leading researchers in the Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong Eye Hospital in Kowloon, Hong Kong, has shown that the catechins in green tea were able to pass the blood-retinal barrier and were found in varied concentrations in different parts of the eyes of rats that were used as subjects. Gallocatechin (GC) was found in the highest concentrations in the retina and epigallocatechin (EGC) in the aqueous humor, with other catechin forms showing up in different areas of the eyes. Interestingly, EGCG showed up only weakly in the different tissues of the eye. The researchers also discovered that some of the catechins were maintained at high levels of concentration – in some areas, for up to 20 hours.
An important question here is whether having various catechins present in tissues (especially those other than the highly reputed EGCG) necessarily means there is a beneficial effect. One of the ways to assess the health benefits of polyphenols is to determine if they have an anti-oxidative effect in the body. Oxidative damage to tissues is the result of free radicals (reactive oxygen species) that can be destructive to cells and DNA. Some of the most significant effects of prolonged exposure to oxidative stress in the eyes are the formation of cataracts, damage to retinal tissue, and glaucoma. Kai On Chu and his colleagues measured the levels of 8-epi-isoprostane in the eyes of the rats, before and after administration of the green tea extract. 8-epi-isoprostane is a compound, the presence of which indicates oxidative damage to tissues. The post-test measures of this compound in the eye showed significant decreases, maintained throughout the entire study period, showing that the catechins in the administered green tea extract had substantial anti-oxidative effects.
I believe there are two important lessons to take from this study. One is that, as always, it is important to take the results of studies that use in-vitro or animal models cautiously, as these models don’t always translate to similar effects in the human body. The second lesson of interest to me is the fact that EGCG had a weak effect in the eye. I believe this is important because of the issue of using isolated constituents vs. the whole substance. I have written about this issue many times before (you can read a related comment I made to a recent post), and believe it important enough to continue to repeat. As a result of the findings of this study, we can extrapolate that if someone were to take a concentrated extract of just EGCG, they would not reap the benefits of the significant anti-oxidant effects that the other catechin compounds, like GC and EGC, have on eye tissue.
The take-away lesson here is to make sure that you drink a variety of teas that are of different types as well as within the same variety. No two plants are exactly alike and each contains different concentrations of a variety of healthy compounds. The same holds true for food. Variety is more than just the spice of life; it is life itself. I hope this helps you to see your way to drinking more tea.