A 2004 study  by the American College of Physicians found that consuming green tea can reduce the chances of forming kidney stones. The study followed a cohort of over 81,000 women in order to determine any correlation between the formation of kidney stones and the drinking of a number of beverages, including green tea. Out of all of the women 719 of them formed kidney stones. By administering a questionnaire regarding beverage consumption, the researchers were able to find out if women who drank green tea were more or less likely to develop kidney stones.

The report found that in general, women who consumed large amounts of liquid were less likely to develop kidney stones. However, some beverages seemed to offer more protection than others. For example, the researchers found that for every eight ounce serving of green tea consumed daily, the chance of developing kidney stones was reduced by eight percent. Hence, the consumption of green tea is more powerful as a preventative measure than drinking beverages in general.

Another recent study coming out of Japan has confirmed the findings in this study using a laboratory based approach.  In the Japanese study, researchers tested a group of laboratory rats to see if treatment with green tea would reduce the risk of the formation of kidney stones. The researchers found that giving rats green tea supplements in their water supply prevents or slows down the development of kidney stones.

Kidney stones are the result of deposits formed from combinations of calcium and oxalate. For this reason, the researchers in the Japanese study concluded that green tea’s abundance of antioxidants is what prevented the formation of calcium oxalate. This is good news as green tea contains a very large amount of antioxidants, far more than in black tea.

A third study performed in 2006 by Korean biologists  reproduced similar results in another laboratory based study using rats. Once again, rats given green tea were less likely to form kidney stones and had lower levels of oxalate in urine samples. Furthermore, in this study, researchers isolated the compound EGCG, the main antioxidant in green tea, and found that this compound seems to be responsible for green tea’s anti-kidney-stone properties.

One fact that should be mentioned is that the highest concentration of antioxidant found in tea are in unbrewed green tea leaves. For example, EGCG—the same antioxidant that was isolated in the Korean study—is present in quantities as much as 100 times greater in tea leaves than in brewed tea, according to a data table published by the USDA.  The data in this table on green tea leaves was averaged from seven different sources comparing the antioxidant concentrations in different forms of black and green tea. While no studies have been performed as of yet directly comparing the health benefits of drinking green tea and eating green tea leaves, it is clear that the compounds that scientists value in green tea are available in overwhelmingly larger numbers in whole green tea leaves.