Here is an informative article worth reviewing.
The Truth about Green Tea
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The important note is that beverage experts suggest no more than 5 cups (40 ounces) of tea daily for a healthy adult, for a maximum intake of no more than 400 milligrams of caffeine daily. While green tea is likely safe for most adults in moderate amounts, too much green tea can bring about side effects due to the caffeine content.
The other important note is that green tea can also decrease the absorption of iron and folic acid. Therefore it is best to be drink tea between meals rather than using it as your mealtime beverage. Wait 1-2 hours between eating foods rich in iron and folic acid and drinking tea to maximize your absorption of these nutrients.