and Alternative Medicine (NCCAM), a government
organization within the National Institutes of Health,
is sponsoring clinical trialsto determine safety and effec-
tiveness green tea as a treatment for more than a dozen
diseases and disorders. Individuals interested in partic-
ipating in a clinical trial at no charge can find a list of
open trials athttp://www.clinicaltrials.gov.
CANCER.Many claims have been made that regu-
larly drinking green tea can help prevent skin, esoph-
agus, stomach, colon, pancreas, lung, bladder,
prostate, and breast cancer. The basis for these claims
lies in laboratory experiments with EGCG. In cell
cultures and in some animal studies, EGCG has been
found to kill cancer cells and to shrink tumors, possi-
bly by preventing blood vessels from growing into the
tumor (a process called angiogenesis) and thus cutting
off the tumor’s supply of food and oxygen. Human
studies have shown mixed results. For example, one
study found that green tea protected against the devel-
opment of esophageal cancer, while another found it
had no effect. In a large study of more than 40,500
Japanese, researchers found that participants who
drank green tea regularly were less likely to die of
cardiovascular disease (e.g. heart attack, stroke) but
just as likely to die of cancer as non-tea drinkers.
There are many difficulties associated with study-
ing the role of green tea in the development of cancer
in human populations. These include:
The amount and strength of green tea and green tea
extract are not standardized and a wide range of
doses are used in different studies.
Many studies done on green tea are poorly designed
so that it is impossible to show a direct link between
cause and effect, or they poorly reported, making
analysis of the results difficult.
Many human studies have a small sample size.
Cancer takes a long time to develop, making it diffi-
cult to follow study participants and determine
outcomes.
Many studies are sponsored by tea growers, manu-
facturers, or importers who have a financial interest
in obtaining positive results.
Despite these drawbacks, the possibility that
EGCG and other antioxidants in green tea can slow
or prevent cancer is strong enough that many research
studies are being supported by government health
agencies around the world. The official position of
the American Cancer Society states, ‘‘ While the
results of lab studies have been promising, at this
time there is no conclusive evidence that green tea
can help prevent or treat any specific type of cancer
in humans.’’
WEIGHT LOSS.Some studies in mice have shown
that the polyphenols in green tea lower the level of
blood glucose (sugar), lipids (fats), and cholesterol,
and reduce the amount of body fat deposited under
the skin. Other studies have shown that green tea
increases bodymetabolism. However, these results
have not been rigorously duplicated in humans.
Although green tea may be good food for dieters
when used in conjunction with a calorie-reduced diet
and increased exercise, it is not a magic bullet that will
cause weight loss by itself.
MENTAL PERFORMANCE.Any effects of green tea
on mental alertness and performance are most likely
due to the effects of caffeine and caffeine-like com-
pounds found in green tea.
CARDIOVASCULAR DISEASE.Claims have been
made green tea decreases cholesterol and fats in the
blood. This is thought to reduce the risk of clogged
arteries and thus help prevent heart attack and stoke.
There is not enough reliable evidence to determine if
these claims are true. One large study done in Japan
did show improved cardiovascular health in individu-
als that used green tea, but these individuals tended to
be thinner than the average American and have other
dietary differences. It is not clear how the Japanese
results might apply to other populations.
OTHER HEALTH CLAIMS.The tannins in green tea
have an astringent or drying effect. One folk remedy to
stop the bleeding where a tooth has been extracted is to
bite down on a used tea bag. Tannins in green tea may
also be responsible for helping to control diarrhea.Precautions
Green tea has been safely used for thousands of
years. Most negative effects are attributable to the
caffeine it contains. Children and pregnant and breast
feeding women may want to avoid the effects of caf-
feine by choosing decaffeinated green tea.Interactions
There are no known drug or herbal interactions
with green tea when used in moderate quantities.Complications
Green tea is generally safe and complications are
few even when large amounts of tea are drunk. The
safety of green tea extract has not been established.
Individuals with hypersensitivity to caffeine or who
use large amounts of green tea may develop caffeine-
related insomnia or upset stomach. The tannin in
green may contribute toirondeficiency in individualsGreen tea