Drinking lemonade could help prevent painful kidney stones, new research shows.

Regular consumption of the refreshing drink -- or even lemon juice mixed with water -- may increase the production of urinary citrate, a chemical in the urine that prevents the formation of crystals that may build up into kidney stones.

So conclude two studies presented Tuesday at the American Urological Association annual meeting in Atlanta.

Kidney stones develop when minerals from urine crystallize and build up on the inside of the kidney. In most people, urine contains a chemical that prevents crystal buildup, but that chemical does not work in people prone to kidney stones. When the body tries to remove the crystallized deposits through the narrow tubes of the urinary tract, a person may feel pain and burning.

In the study led by Kristina Penniston, an assistant scientist in the Department of Surgery at the University of Wisconsin School of Medicine and Public Health, researchers retrospectively examined the medical records of 100 patients who had been prescribed lemonade therapy after seeking treatment for calcium oxalate kidney stones. Calcium oxalate stones are the most common type of kidney stones.

"We'd been recommending lemonade therapy for about 10 years, but within the last five or six years, we really noticed that people on lemonade therapy have extremely high urinary citrate concentrations," Penniston said. "We knew people were seeing results in urine biochemistries, and [lemonade therapy] was fairly well-tolerated."

About two thirds of the patients drank about 4 ounces of pure lemon juice that they poured into 2.5 liters of beverages throughout the day or 32 ounces of low-sugar or low-calorie prepared lemonade, Penniston said. The remaining patients in the study were treated with a combination of lemonade therapy and potassium citrate, a medication that maintains the antacid level in urine.

After an average treatment time of about 40 months, "in both groups, urinary citrate increased and so did urine volume. But the increase in volume was only significant in groups with lemonade therapy," Penniston said. For patients prone to kidney stones, drinking lots of fluids and increasing urinary volume may help prevent future stone formation.

In another study presented at the conference, conducted by researchers at Duke University, 12 patients with mild-to-moderate hypocitrauria -- a condition that causes a person to produce low levels of urinary citrate -- drank 120 milliliters of lemon juice mixed with two liters of water throughout the day.

After the researchers compared the people treated with lemonade therapy to patients taking potassium citrate, results showed that 11 of the 12 patients had increased urinary citrate levels during lemonade therapy.

The kidney stones of the people taking lemonade therapy also decreased in size and number during the course of the treatment, which lasted an average of 41 months.

Although the results of these two studies indicate that lemonade therapy may offer a simple alternative treatment to people with kidney stones who can't tolerate taking potassium citrate, much more research needs to be conducted, both study authors concluded.

"Both of these studies are addressing a very specific individual -- individuals with low urinary citrate. They're not suggesting that everyone with a stone problem try this," said Dr. Eric N. Taylor, of Brigham and Women's Hospital and Harvard Medical School, both in Boston.

Taylor also noted that the type of lemonade used in therapy may easily add extra sugar or calories to a person's diet. "The problem is, if someone would just drink 2 liters of lemonade, it could represent a significant amount of calories and sugar," he said. "When people think lemonade, they don't necessarily think of lemon juice. The key is you need real fruit," he said.