August 23, 2010

More on Tea and Eye Health

Korean Drum Dancers

I am sure each language has its own version of the popular Chinese
phrase "Eyes are the Gate for your Soul".  According to the
informative video on cataract, most people will develop the
problem sooner or later in the old age.  Can you image the
deprivation of being not able to distinguish the pink/red or the
coming/going of the dancers in the above picture? 

Since tea catechins have been frequently quoted along with other
antioxidant-rich foods, Vitamin A &C, phenolic compounds...
for both general and eye health, I requested my old time college
classmate Dr. Ing-ming Jeng (recently retired professor/researcher
in biochemistry field) to clarify the overlapping and confusing terms
for my understanding.   He did a thorough research and untangled
the terms from their structural and biological character viewpoints.
His reply is truly worthy of at least 75% of my blog page instead of
"one cent" as he jokingly subtitled in his reply.  In order for the
readers to share his scholarly insights,  I decide to copy my
question and his reply below. 

My request email dd July 27:
Several friends and I attended an eye health presentation by a local
specialist this past Saturday. For followup, I dug up my previous blog entry
on the topic and shared with them
However, after a closer read, I found the questionable sentence in
the linked article I included in the blog .  I am concerned about the accuracy
of the sentence in that report: "Catechins include vitamin C, vitamin E,
lutein and zeaxanthin." .....

Dr. Jeng's reply dd Aug 16:
I want to thank you for drawing my attention to Catechins and
green tea. The subject matter is interesting and you convince me to
drink more green tea. We actually went to our favorite Japanese
restaurant and drank some green tea last night.

I am slow in response as I tried to find the recent original
publication online with no avail. I am not sure that you are aware of
the fact that I am retired now. Therefore, I have no access to
academic data-base. In short, I will give you my 2-cents (probably
worth only 1 cent) from what I have learned online.

I agree with your doubts about the statement's accuracy "Catechins include
vitamin C, vitamin E, lutein and zeaxanthin." in the article.... It is incorrect and needs some clarification.  I will give my best try below.


There are three overlapping terms: anti-oxidant, polyphenol
compund and catechin.  Polyphenols and catechins are defined
structurally, and anti-oxidant is a functional defination.

Catechins definitely do not include the 4 mentioned anti-oxidants.
However, a close examination of the structure of four non-catechin
anti-oxidants may tell you about their relationship with polyphenol

A. A polyphenol antioxidant is a type of antioxidant containing a polyphenolic substructure. It is important to recognize that this is a chemical definition and several phenolic structures must be
presented in the compounds to be called polyphenol. .   Catechins belong to polyphenolic antioxidant compounds.

B. Although vitamin C (ascorbic acid) is an anti-oxidant, it is not a polyphenol compound. It is derived from glucose and is devoid of any phenol structure.

C. Lutein does not have a phenolic group. Structurally, it is related to retinal or retinol. It has two hydroxyl groups that are linked (conjugated) to long string of conjugated double bonds so it is easily oxidizable. The structure contributes to its anti-oxidant property. Again, the compound is an anti-oxidant but is not a polyphenolic antioxidant.

D. Similarly, I probably would not call zeaxanthin a polyphenolic compound. Lutein and zeaxanthin have identical chemical formulas and are isomers, but they are not stereoisomers. The only difference between them is in the location of the double bond in one of the end rings.