Green tea extract is derived from leaves of camellia sinensis, the plant from which green, black and oolong teas are made. It is associated with several health benefits, many supported by preliminary scientific research. This includes potential cancer-fighting properties, and a strong antioxidant effect that protects the body from the damaging effect of free radicals. The scientific community notes, however, that continued research is necessary.
Green tea has been used for medicinal purposes in India and China for nearly 5,000 years. It is made by lightly steaming the leaves before allowing them to dry, which helps retains the active properties of the plant. Oolong tea is made by allowing the leaves to ferment slightly before drying, and black tea is made by allowing the leaves to ferment longer. Fermentation breaks down the active ingredients, making green tea or its extract the tea of choice.
Green tea extract, like many herbs, is standardized in the production phase to guarantee that a certain percentage of the active ingredients remain present in the final capsulized form. The active ingredients are polyphenols in the form of flavonoids like catechins and epigallocatechin gallate (EGCG). Polyphenols, flavonoids, catechins and EGCG are powerful antioxidants that appear to interfere with and reduce the spread of certain types of cancer cells. The antioxidant activity of EGCG in green tea extract is purportedly up to 100 times more powerful than that of vitamin C or E.
Among populations in China and Japan, where high amounts of green tea are consumed daily, cancer rates are statistically lower. There is now growing scientific research from reputable sources that shows promising results as to how the active ingredients in green tea might be responsible for lowering rates of various kinds of cancer.
UCLA's Jonsson Comprehensive Cancer Center, an award-winning cancer research center, reported in their 2005 Cancer Discoveries newsletter that several published, peer-reviewed studies indicated that green tea extract “induces death in cancer cells” without affecting healthy cells, and prevents cancer cells from producing the “independent blood supply” required to spread to other parts of the body. This indicates that the extract might help to keep cancer contained, making it easier to treat.
Studies conducted by other respected universities and clinics have also showed promising results involving breast, liver, lung and colon cancer, among others. The Mayo Clinic conducted a small study using four patients with chronic lymphocytic leukemia (CLL). Three of the four patients showed significant regression of CLL after taking green tea extract for a period of a few months. The fourth patient’s prognosis was improved, but not significantly. A larger trial is needed to see if these results can be repeated with consistency.
Green tea extract might also be beneficial in improving cardiovascular circulation by reducing LDL or “bad cholesterol,” suppressing appetite and improving oxidation of fat. These claims are not widely accepted by the scientific community, however, because they are based on animal models and only a few human studies.
When purchasing this extract, shoppers should look for a product that is standardized to a minimum of 90% polyphenols and 55% EGCG. Using this standard, a 500-milligram (mg) capsule will contain 275 mg EGCG, (500 mg x 55% = 275 mg). The suggested daily dose, according to some sources, is approximately 2 cups (473 ml) of green tea per day, or the equivalent of 200 to 400 mg EGCG per day. Note that green tea contains natural caffeine. Processes that remove the caffeine may also diminish the potency of active ingredients.
The quality of green tea extract will vary between brands, so consumers should read the labels carefully and not exceed the recommended dosage. This supplement should not be used instead of professional medical care, and is not recommended for pregnant or lactating women. People should visit a healthcare professional regularly and follow a healthy routine of diet and exercise for optimum health.