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With a wide number of health benefits and soothing effects, it's not a surprise that the world continues to enjoy tea from generations to generations. But as years go by, people began to speculate several health disadvantages that could potentially be associated by drinking tea. And one of these disadvantages is that it might cause kidney stones.

What is a kidney stone?

In simplest terms, a kidney stone is the formation of a hard mass found in the kidneys. It is usually caused by insoluble calcium oxalate compounds; however some dietary factors also increase the risk.

What relates tea to kidney damage?

Foods rich in calcium oxalate are believed to contribute a lot to the formation of kidney stones in the body of adults (about 80%). Some of these foods are spinach, beets, nuts, berries, tea, among others. Because tea belongs to this group of foods and beverages, it was believed to contribute to kidney stone formation in the body.

Studies relating to tea and oxalate

A research from the Institute of Science and Engineering Techniques in the University of Angers in France and the Food Group, Animal and Food Science Division of Lincoln University in Canterbury, New Zealand, discovered that a mean value of 12.21mg of oxalate (5.1 to 16.4 mg) per cup of tea can be consumed from loose-packed black tea leaves. Meanwhile, loose green tea leaves and oolong tea supply a mean value of 0.3 to 1.7 mg oxalate per cup.

For the information of the general public and especially for the benefit of people with kidney problems, foods are classified according to their oxalate content per serving. Very high oxalate foods have greater than 50mg oxalate content/serving, high oxalate with 10-50mg/serving, moderate oxalate with 2-10mg/serving and low oxalate with less than 2mg/serving. As we can see, black tea falls under moderate oxalate. And the University of Pittsburgh Medical Center recommends to take no more than three servings of moderate oxalate foods. Green and oolong teas however, fall under low oxalate foods and are found to be safe and could be enjoyed as many times as you like.

However, a study conducted by the Harvard Medical School and the Harvard School of Public Health in Boston, Massachusetts, it has been found that men without kidney stones consume 214 mg of oxalate per day on the average, older women with 185mg/d, and younger women with 183/d. Therefore, if one should drink 6 cups of black tea a day, (considering that it's only black tea that he's consuming on a 24-hour diet) it will give him a mean value of 73.26 mg/d (30.6 to 98.4 mg/d). Considering these values, a person (male) on a worst case scenario has an allowance still of 115.6 mg/d of oxalate, 86.6 mg/d for an older woman and 84.6 for a younger woman. But of course, this isn't always the ideal picture.

The numbers only imply that drinking tea, whether green, oolong or black, isn't something one should worry about. But if you''re already a kidney patient, then it is always best to follow your doctor's advise. Just bear in mind that there are still a number of risk factors to consider, and other dietary intakes that could possibly trigger the condition. Naturally, anything that is taken too much has its own hazards, that's why it is always good to take everything in moderation. 

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