Green Tea

Latin name: Camellia sinensis (L.) Kuntze [Theaceae]
Latin synonyms: Thea sinensis L.
Plant part: Leaf

Chinese legend has it that tea was discovered in 2700 B.C. when a
gust of wind blew some tea leaves into a kettle of boiling water. A
competing legend advanced by the British East India Company
claims tea originated in India and not China (Gutman and Ryu, 1996).
Green tea and black tea are both derived from the young shoots
(the first two or three leaves plus the growing bud) of Camellia
sinensis (L.) Kuntze. The teas are differentiated by their method of
processing. Heating the freshly picked leaves shortly after harvest
produces green tea. This process inactivates enzymes (polyphenol
oxidases) that form the dark pigments associated with black tea. The
heated leaves are then rolled to squeeze the juices to the surface of the
leaf and dried using hot air. Black teas are produced by a natural enzymatic
fermentation of the leaves that occurs after harvest (Gutman
and Ryu, 1996).


A cup of green tea usually contains 300 to 400 mg polyphenols.
Polyphenols are a large class of mildly acidic compounds with antioxidant
properties. Polyphenols can be divided into many subclasses,
including catechins, an example of which is epigallocatechin gallate
(EGCG) (Gutman and Ryu, 1996).

Studies of green tea as tea solids or extracts have been conducted
exploring its use in weight loss and as an antioxidant useful in reducing
cardiovascular risk factors, in alleviating the adverse effects of renal
insufficiency, and in reducing the negative effects of cancer therapy
on blood cells. On balance, green tea extracts and green tea have
positive effects on metabolism and antioxidant activity. However, the
impact of these effects on health outcomes remains to be determined.

Weight Loss

A study exploring green tea’s effect on weight loss was conducted
using Exolise, one capsule three times daily. This mechanistic study
showed an increase in energy expenditure over a 24-hour period with
Exolise compared to placebo. The energy expenditure was 4 percent
above the stimulatory effects produced by equivalent amounts of caffeine
found in Exolise (Dulloo et al., 1999). Although this carefully
controlled study demonstrated thermogenic activity and promotion
of the oxidation of fat, the results were of questionable significance
for clinical weight management. A follow-up study with moderately
obese subjects did report weight loss as a result of treatment. How
ever that study did not include a control group, and thus did not qualify
for review in this book (Chantre and Lairon, 2002).

Cardiovascular Risk Factors/Antioxidant Activity

Potential antioxidant activity was explored in two studies comparing
green and black teas. In a study with 45 participants, the daily
consumption of six cups of green or black tea (Lipton tea solids, 0.5 g
in 150 ml water) over a four-week period did not lead to any effect on
serum lipid concentrations, resistance of low-density-lipoproteincholesterol
(LDL) to oxidation, or to markers of oxidative damage to
lipids. However, consumption of green tea led to a slight increase in
total antioxidant activity in plasma (van het Hof et al., 1997). The
other study included 21 adults who received six different treatments
on six different days with at least two days in between treatments.
The administration of a single dose of 2 g of green or black tea solids
(Lipton) in 300 ml water led to a significant increase in plasma catechin
levels and in plasma antioxidant activity one hour later. The rise
in total catechins was greater with green tea than black tea, as expected
based on the higher content of catechins in green tea compared
to black tea. The addition of milk to either green or black tea did not
affect results (Leenen et al., 2000). These studies were both rated as
low in quality due to a lack of blinding and poor descriptions of the
randomization process.


 Hematopoietic Effects of Cancer Therapy

A study examined the potential protective effect of a green tea
polyphenol extract (Xin Nao Jian) on the damage to the development
and formation of blood cells due to cancer radiation therapy or chemotherapy.
Sixty cancer inpatients with a normal blood cell profile
undergoing their first treatment were included in the study. They were
given 200 mg of extract three times daily, another herbal formula for
improving blood quality (Sha Gan Chun), or no additional treatment
for one month. Total white blood cell counts improved in the green
tea group but declined in the Sha Gan Chun group after five weeks
 and in the control group after three weeks. No significant changes
were observed in hemoglobin levels or platelet counts in any group
(Walsh, 1997a). Our reviewer, Dr. David Heber, commented that the
effects of green tea on lymphocyte stabilization and immune function
deserve further study. This study was limited by inadequately described
statistical methods and a small sample size.



 Renal Insufficiency

In another study, Tegreen was given in the same dose (200 mg
three times daily) to patients with chronic renal insufficiency for
three months. Renal function (as measured by blood urea nitrogen)
was improved, erythrocyte superoxide dismutase activity was significantly
increased, and plasma lipid peroxide levels were significantly
decreased. The author of the study commented that the benefits of
Tegreen to this population were due to its antioxidant activity and free
radical scavenging activity (Walsh, 1997b). Although it had some serious
methodological flaws, this study remains a good guide for future
studies.

 Cardiovascular Risk Factors

A small study using a green tea concentrate, Polyphenon E, measured
the effect of 300 mg extract twice daily, the equivalent of seven
to eight cups of tea, on markers of antioxidant activity in the blood
compared to untreated controls. After one week, plasma catechin levels
were measurable, whereas they were not detectable at baseline.
No effect was reported on the concentration of plasma lipids or on
lipid peroxides compared to baseline. However, an increase in resistance
to oxidation of LDL-cholesterol was measured ex vivo (Miura
et al., 2000). The study was weak due to the small sample size and the
lack of blinding and randomization of patient populations.