The Benefits of Green Tea
Disclaimer: All information provided should be considered as generalizations and not as specific information for any individual. Nor should this information be considered medical advice. This information needs to be considered in consultation with your family physician. Specific food allergies or medical conditions may make the provided information unsuitable for some individuals.
What is Green Tea?
Tea, in general, is derived from the leaves of the Camellia sinensis plant. The three main types of tea are: green (no "fermentation"), oolong (moderate "fermentation"), and black (complete "fermentation"). When tea leaves are harvested and immediately steamed or heated the polyphenol oxidase that is present in the leaves is inactivated and green tea is produced. If the leaves are "harvested, withered, rolled, and crushed" the polyphenol oxidase is liberated and oxidized leading to theaflavins and thearubins which color the tea yellowish-orange to reddish-brown. These colored teas apparently have less active antioxidant constituents.
Green tea has the highest amount of catechins per gram of all the tea types. Quercetin, kaempferol and rutin are the most important flavonols in tea. They can also be found in red wine, black grapes, apples, onions, cherries, berries, grapefruits and cruciferous vegetables.
On a side note, a cup of tea typically contains 40 to 55 mg of caffeine whereas a cup of coffee contains 125 to 150 mg.
The polyphenols in tea have demonstrated effects as antioxidants, modulators of blood clotting consituents (platelets) and vascular tone in the body. Green tea has also been shown to reduce cholesterol in animal models.
The Asian Paradox
The term "Asian paradox" refers to the epidemiologic observation that despite very high consumption of tobacco products in Asia the rates of heart disease, stroke, and lung cancer are among the lowest in the world.
This may be in part explained by the local diets which include a large amount of fish as compared to Europeans and North Americans. (see The Benefits of Fish).
The other complimentary hypothesis is that the high consumption of Green Tea may also play a role. Green Tea has reputed benefits in prevention of vascular disease (heart and stroke) as well as cancer.
A recent survey conducted in the US among cancer patients revealed that the most commonly used herb was green tea (54% of all patients).1
Monika sampling Green Tea in the Ginza District of Tokyo. We
were amazed by the diverse teas readily available all over Japan.
So what does the medical evidence suggest?
A recent meta-analysis (a type of study that combines all of the available data from multiple studies in the attempt to provide a statistically higher-powered answer to a particular question) reviewing 17 different studies reported an 11% decrease in myocardial infarctions (aka. heart attacks) when three cups of Green tea were consumed daily.2
When comparing a total of 340 individuals who drank any green tea at all (one or more cup) versus those who did not drink at all there was a 44% reduction in myocardial infarctions.3
Even in patients with a previous history of myocardial infarction, mortality (aka. death) was decreased significantly in moderate drinkers (<14 cups/week) and in heavy drinkers (14 cups/week) when compared to non-drinkers. This study followed 1,935 patients.4
A study involving 8,552 also demonstrated a reduction in the risk of both myocardial infarctions and cancer among drinkers of green tea.5
It is believed that the active constituents in green tea are the high concentrations of polyphenolic flavonoids. Flavonol intake has been demonstrated to similarly lower risk of cardiovascular disease.6
A study of asian women living in Los Angeles, California demonstrated that significantly more women without breast cancer (control group) than women with breast cancer drank green tea.7
A Word of Caution
Epidemiologic studies examining differences between Asian and Western populations are supportive of the benefit of green tea. There is also evidence in animal models that it is beneficial. However, the studies described above although impressive in their numbers do leave much to be desired in the way they were performed and interpreted.
Comparing two groups of individuals and ascribing a difference between them (i.e. number of heart attacks) and attributing that to one factor (i.e. Green Tea) is difficult and may give misguided impressions. None of the above studies was a double-blinded placebo- and randomized- controlled trial which is the high standard form of comparison of an intervention's (i.e. Green Tea) effect on a particular disease. These studies need thousands of patients and need to be constructed in very specific ways to be reliable. The above studies are of poorer quality in the grand medical science scheme of things.
To Drink or Not to Drink
Does that mean their results are valid? I would suggest the results are
compelling but not yet conclusive. Although at the same time Green Tea is
inexpensive, has no concerning side effects that I am aware of and may
potentially be very helpful in preventing heart disease, stroke and cancer.
I for one will be taking the Green Tea out of the cupboard more often.
Dr. Lawrence Korngut, M.D.
Chief Neurology Resident
London Health Science Centre
London, Ontario
Many of the details of green tea research and the preparation process were adapted from:
Sumpo BE et al., Green Tea, the "Asian Paradox" and Cardiovascular Disease. Journal of the American College of Surgeons. 2006
References
1 Bernstein BJ., Prevalence of complementary and alternative medicine use in cancer patients. Oncology 2001;15:1267-1272.
2 Peters U., Does tea affect cardiovascular disease? A meta-analysis. American Journal of Epidemiology 2001;15:495-503.
3 Sesso HD., Coffee and tea intake and the risk of myocardial infarction. American Journal of Epidemiology 1999;149:162-167.
4 Mukamal KJ et al., Tea consumption and mortality after acute myocardial infarction. Circulation 2002;105:E9109-E9110.
5 Imai K., Cancer-preventative effects of drinking green tea among Japanese population. Preventative Medicine 1997;26:769-775.
6Sumpo BE et al., Green Tea, the "Asian Paradox" and Cardiovascular Disease. Journal of the American College of Surgeons. 2006
7 Wu AH, Green tea and risk of breast cancer in Asian Americans. International Journal of Cancer 2003;106:574-579.