According to the University of Pittsburgh Medical Center, approximately one million Americans get kidney stones every year. The most common type of kidney stone, called a calcium oxalate stone, forms when the urine contains high concentrations of a substance called oxalate, which comes from your diet. Many teas are high in oxalate. If you are prone to developing kidney stones and drink tea regularly, you may develop calcium oxalate stones.
Physiology
When you drink some types of tea, your digestive system breaks it down, forming oxalate as a waste product. Normally, oxalate travels throughout your bloodstream until it reaches the kidneys, where it is filtered out of your blood and excreted from your body through your urine. If your urine contains normal amounts of oxalate, it will remain in solution and not cause any problems. If your urine contains abnormally high concentrations of oxalate, however, the waste product can come out of solution and combine with calcium to form hard stones.
Low-Oxalate Diet
If you are prone to developing calcium oxalate kidney stones, your doctor may recommend a low-oxalate diet. When following a low-oxalate diet, you should limit your oxalate intake to 40 to 50mg of oxalate per day. A low-oxalate diet prohibits high-oxalate foods, which contain at least 10mg of oxalate per serving, and allows two to three servings of moderate-oxalate foods, which contain between 2 and 10mg of oxalate per serving. Most of your food intake should be in the form of low-oxalate foods, which contain less than 2mg of oxalate per serving.
Oxalate and Tea
Black tea contains 10mg of oxalate per serving, which classifies it as a high-oxalate beverage. Because drinking just three cups of black tea per day can provide more than half of your daily allotment for oxalate, you should avoid black tea when following a low-oxalate diet. Some varieties of tea, such as rosehip tea, Matetea tea and black currant tea, which contain 2 to 10mg of oxalate per serving, are classified as moderate-oxalate beverages. Limit your intake of these teas. Green teas and herbal teas are classified as low-oxalate beverages, which means that they contain less than 2mg of oxalate per serving. If you cannot remove tea from your diet completely, drink green tea or herbal tea rather than black tea or moderate-oxalate tea varieties.
Considerations
Drinking water is an important step in preventing kidney stones. Water helps promote urination, which allows the kidneys to remove excess oxalate from the body. The National Kidney and Urologic Diseases Clearinghouse recommends drinking 12 8-oz. glasses of water per day.
In addition to oxalate, many teas also contain caffeine, which acts as a natural diuretic. Caffeine causes your body to lose water more quickly, which can increase the concentration of oxalate in your kidneys. To counteract this effect, drink an extra glass of water for every cup of tea that you drink.
