The only beverage consumed more often than tea is water, and drinking tea may be beneficial for your health, possibly limiting your risk for cancer and heart disease due to the antioxidants found in tea, according to an article published in the "European Journal of Clinical Nutrition" in July 2006. However, tea contains a substance called oxalic acid, which may have some detrimental health effects.
Oxalic Acid Content of Tea
The amount of time tea is steeped and whether you stir it can influence the oxalate content of brewed tea, as does the brand of tea you choose and the contents of herbal teas. Black tea contains the most oxalates, averaging 12.21 milligrams per cup if made with loose tea and 9.54 milligrams per cup if made with tea bags. Green tea averages 1.36 milligrams per cup, Oolong tea averages .58 milligrams per cup and herbal teas average .84 milligrams of oxalate per cup, according to a study published in the "Asia Pacific Journal of Clinical Nutrition" in 2002.
Consuming foods containing high levels of oxalates increases your risk for kidney stones, especially if you suffer from calcium oxalate stones. The Oxalosis and Hyperoxaluria Foundation recommends avoiding black, green and white teas if you suffer from Enteric Hyperoxaluria, but says that if you suffer from kidney stones due to other reasons, you may not need to avoid these beverages as long as you consume enough calcium in your diet.
Oxalic acid can bind with certain minerals, including calcium and iron. This means if you add milk to your tea you may not benefit as much from the calcium it contains. However, the amount of oxalic acid in tea is unlikely to cause a problem for you unless you are already deficient in these minerals or drink very large amounts of tea.
Follow the advice of your doctor to determine which types of tea and how much it is safe for you to drink if you suffer from kidney stones. Avoid black tea and stick with green, white or herbal teas. These contain much smaller amounts of oxalate, so they are less likely to cause an increase in your risk for kidney stones.