Green tea contains six times the antioxidant levels of black tea and Japanese green tea contains the highest amount.

Historians believe that tea was first drunk thousands of years ago, when the ancient Chinese started boiling their water to guard against bacterial contamination and added tea leaves as flavouring.

Though it has its origins in that simple practice, extraordinary healing properties have come to be associated with tea over the centuries. 16th century European explorers, who encountered tea for the first time in the Far East, reported that it was a hot, medicinal drink used to relieve fever, headache, stomach ache and joint pain.

Recent research confirms what Eastern healers have long known: that drinking green tea may not only help to prevent heart disease and strokes, but may also regulate blood sugar, lower blood pressure, boost the immune system, facilitate weight loss, help prevent ulcers, slow the ageing process, fight viral colds and flu, and even prevent gum disease, cavities and bad breath (1), reduce bone loss in elderly women (5).

Furthermore, Asian populations, where green tea is consumed as part of the every day diet tend to have a lower incidence of cancer than people in countries where green tea is less commonly drunk. Consequently, green tea has been the focus of considerable amount of research in recent years and has been associated with reducing the risk of many types of cancer.

Lately, two 2007 prospective studies found a significant relation between regular green tea consumption and the reduction in risk for both colon and rectal cancers in women (3), and a dose-dependent decrease was shown in the risk of advanced prostate cancer (4).

Many of these possible health benefits come from green tea's rich supply of catechins (also referred as polyphenols, which they belong to), which are one of nature's most powerful antioxidants. Even though black tea and green tea come from the same variety of tea bush, black tea can loose up to 10 times of its health promoting properties during fermentation.

Research has shown that green tea has significantly superior antioxidant levels of black tea, and that Japanese green tea, as a result of its special steaming process, contains the highest amount of all (2).

References
(1) Cabrera C, Artacho R, Gimenez R, Beneficial effects of green tea - a review, J Am Coll Nutr 25 (2):29-99 (2006)
(2) Cheng TO, All teas are not created equal: the Chinese green tea and cardiovascular health, Int J Cardio, 108(3): 301-8 (2006)
(3) Yang G et al., Prospective cohort study if green tea consumption and colorectal cancer rick in women, Cancer Epidemiol Biomarkers Prev. 2007; 16: 1219-1223.
(4) Kurahashi et al., Green Tea Consumption and Prostate Cancer Risk in Japanese Men: A Prospective Study, Am J Epidemiol. 2007 Sep 29.
(5) Devine A. et al., Tea drinking is associated with benefits on bone density in older women, Am J Clin Nutr. 2007 Oct;86(4):1243-7.