Dosage and Side-effects
Green tea extract supplements are accessible over the counter in various forms. Standardized green tea extract is 90 percent total polyphenols, and 1 capsule equals 5 cups of tea.
For a green tea extract standardized for 80 percent polyphenols and 55 percent EGCG, a daily dose of 300 to 400 mg green tea extracts is recommended. Some green tea extracts may have as little as 15 percent polyphenols, usually these are far less expensive. It should be kept in mind that the various components of unpurified green tea extracts have synergistic effects and therefore are better than any individual tea component. Scientists also conclude that tea extracts are better taken between meals in order to avoid decreased iron absorption.
An often overlooked aspect is the fact that EGCG has a poor bioavailability when taken orally; the absolute bioavailability of EGCG in CF-1 mice and Sprague-Dawley rats was found to be only 26.5 and 1.6%, respectively. The bioavailability for humans is assumed to be in the same range.
Though green tea extracts show potential anticancer capacity - under some conditions by working together with other drugs and suppressing multidrug resistance in cancer cells - they are not suggested for use alone as a chemotherapy agent for cancer treatment.
Excessive intake of green tea extracts containing caffeine has side effects; an excessive concentration may act as a pro-oxidant to damage DNA and produce undesirable side effects.
Additionally, use of green tea extracts has been linked to occasional cases of acute liver failure
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