Green Tea Extract - Healthy or Dangerous?

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Bolaleman - 12 Apr 2008 05:21 GMT

It is generally known that green tea has antioxidants which can
prevent from certain diseases and even inhibit the growth of cancer
cells. During the last years there appeared several green tea
concentrates on the market claiming "aiding in weight loss by burning
calories, guarding against flu virus, lowering cholesterol and high
blood pressure, preventing arthritis, cavities and tooth decay,
antiaging, reducing risk of cancer, heart disease and stroke", etc.
This sounds great but according to a study performed by Lambert et al.
(see reference below), pharmacological and toxicological evidence does
indicate that green tea polyphenols can in fact cause oxidative stress
and liver toxicity in vivo at certain concentrations. This would imply
that consumers should exercise caution when consuming herbal products
produced from concentrated green tea extract. Other evidence presented
in the review cautions against the drinking of green tea by pregnant
women.

Ref.: Lambert, J.D., et al., (2007) Possible Controversy over Dietary
Polyphenols: Benefits vs Risks, Chem Res Toxicol

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Mark Thorson - 12 Apr 2008 20:24 GMT

> Other evidence presented
> in the review cautions against the drinking of green tea
> by pregnant women.

That's due to interference with folic acid metabolism.
Folic acid is important for avoiding neural tube
birth defects. Presumably, taking a folic acid
supplement can mitigate this risk. Pregnant women
should be taking a folic acid supplement anyway,
because there's no harm if you don't need it, and
a great benefit if you do.

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Bolaleman - 14 Apr 2008 22:41 GMT

> Bolalemanwrote:
>
[quoted text clipped - 9 lines]
> because there's no harm if you don't need it, and
> a great benefit if you do.

Mark your right. Blocking the folic acid mechanism by inhibiting the
enzyme dihydrofolate reductase (DHFR) is probably the way green tea is
preventing growth of cancer cells as in particular tumor cells need
folic acid to divide.
But everything is a question of concentration. I am sure that drinking
a cup of green tea will not be a problem at all for a pregnant woman,
in particular if taking a folic acid supplement (as you recommend).

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Bolaleman - 23 Apr 2008 14:32 GMT

> > Bolalemanwrote:
>
[quoted text clipped - 17 lines]
> a cup ofgreenteawill not be a problem at all for a pregnant woman,
> in particular if taking a folic acid supplement (as you recommend).

There is an other issue concerning polyphenols that needs to be
considered - the potential effect on liver and kidney function.
According to recent
published studies (http://pubs.acs.org/cgi-bin/sample.cgi/crtoec/
2007/20/i04/html/tx7000515.html), green tea is good for you, but only
if drunk in moderation. The polyphenols in green tea are credited
with
preventing heart disease and cancer but higher doses of these
substances can cause liver and kidney damage. "People shouldn't be
too
alarmed by this, but those taking supplements may experience
problems," says lead author Chung Yang of Rutgers, the State
University of New Jersey.

He stresses that up to 10 small cups of green tea a day is fine.
Problems are likely in people who take supplements, which can contain
up to 50 times as much polyphenol as a single cup of tea. Yang also
reports cases of people who experienced liver toxicity after
overdosing on green-tea-based supplements. Their symptoms disappeared
when they stopped taking the pills, only to return when they started
taking them again (Chemical Research in Toxicology, vol 20, p 583).

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