Your diet can promote or prevent the formation of kidney stones, and the amount of green tea you drink is one possible factor. Green tea contains a substance that may contribute to kidney stones but it has also been tied to their prevention. Understanding how they form and the role of green tea may help lower your risk of developing kidney stones.
Kidney Stone Formation
Kidney stones, also called renal calculi, form when minerals that are normally dissolved in the urine begin to crystallize. Stones can form when the urine is so saturated with minerals that there isn't enough fluid to keep them dissolved or when the body doesn't produce enough of the substances that keep the minerals dissolved. Different minerals contribute to kidney stones but the most common consist of calcium and oxalate, which is a substance found in green tea.
Oxalate in Green Tea
High levels of oxalate in the urine, called hyperoxaluria, cause 60 percent of all calcium stones, according to the University of Maryland Medical Center. Hyperoxaluria can be caused by medical conditions, problems breaking down oxalates or too many oxalate-containing foods in the diet. Eight ounces of green tea contain 1.75 g of oxalate, but the amount varies depending on the strength of the tea, according to The Oxalosis and Hyperoxaluria Foundation. This places green tea slightly below the criteria for moderate oxalate-containing foods. A low-oxalate diet means less than 50 mg of oxalate per day, so the overall effect of green tea depends on the total amount you consume from other foods in your diet.
Kidney Stone Prevention
Green tea may help prevent kidney stones. Research conducted by Chen et al. and published in the journal CrystEngComm in 2010 indicates that green tea inhibits the formation of calcium oxalate crystals. In 2006, the Journal of Endourology published a study titled "Effects of Green Tea on Urinary Stone Formation: An In Vivo and In Vitro Study." Jeong et al. also concluded that green tea prevents kidney stone formation. They believe this may be due to the antioxidant effect of the tea.
Considerations
If you have a history of oxalate-containing kidney stones, then future stones will likely contain oxalate. Limiting the amount of oxalate in your diet will help prevent them. Milk binds with oxalate and prevents it from being absorbed so adding milk to your green tea limits the effect of the oxalate. Talk to your health care provider about how much you may safely consume.
