Q: I've developed kidney stones. Is there anything I might be eating or drinking that could have caused them? I drink two to three cups of mint tea daily--could that be the problem?

A: First and foremost, be sure you drink plenty of fluids every day and avoid dehydration. Kidney stones form when certain minerals concentrate in the urine and form hard crystals. By drinking plenty of fluid, you can decrease the concentration of these minerals. Drink 8 to 12 cups (64 to 96 ounces) a day.

There aren't any particular fluids that you need to avoid. But moderation, as always, is best. Alcohol and caffeine have a diuretic effect, causing the kidneys to make more urine. This is helpful for preventing kidney stones. But if you're drinking too much alcohol or caffeine and not enough water or other liquids, you can dehydrate.

The most common type of kidney stone is the calcium oxalate stone. About 80 percent of all kidney stones are made of calcium oxalate. The name might make you think you should eat a low calcium diet to avoid getting them, but you should actually do the opposite.

The problem is oxalate. Most people who develop calcium oxalate absorb too much oxalate. The extra oxalate is absorbed by the intestines and passed into the blood stream. The body uses what it needs, and the extra oxalate is excreted in the urine. In the urine, the higher concentration of oxalate can combine with calcium to cause kidney stones.

This is where eating enough calcium-rich foods comes in. Dietary calcium binds the oxalate in your intestine. This way, less oxalate can get absorbed into your blood stream and less will need to pass into your urine.

Avoid high protein diets. Higher protein intake, especially from animal protein, increases the likelihood of kidney stones. High-protein diets are acidic and reduce the amount of natural stone inhibitors in the urine. In addition, high-protein diets tend to contain more oxalate.

Tea and coffee in moderation are not a problem. In fact, some studies suggest that drinking moderate amounts of tea and coffee can actually decrease the risk of kidney stones. Tea and coffee do contain some oxalate, but the amount of water in these drinks more than compensates.

The two to three cups of mint tea you're drinking a day (as well as other herbal teas) should not cause a problem, as long as you're drinking additional amounts of other fluids.

(Howard LeWine, MD, is a practicing internist at Brigham and Women's Hospital, Boston, Mass., and Chief Medical Editor of Internet Publishing at Harvard Health Publications, Harvard Medical School.)

(For additional consumer health information, please visit http://www.health.harvard.edu.)