(Medical Xpress) -- This is the peak season for drinking iced tea, but a Loyola University Medical Center urologist is warning the popular drink can contribute to painful kidney stones.
Iced tea contains high concentrations of oxalate, one of the key chemicals that lead to the formation of kidney stones, a common disorder of the urinary tract that affects about 10 percent of the population in the United States.
"For people who have a tendency to form the most common type of kidney stones, iced tea is one of the worst things to drink," said Dr. John Milner, assistant professor, Department of Urology, Loyola University Chicago Stritch School of Medicine.
The most common cause of kidney stones is not drinking enough fluids. And during the summer, people can become dehydrated from sweating. Dehydration, combined with increased iced tea consumption, raises the risk of kidney stones, especially in people already at risk.
"People are told that in the summertime they should drink more fluids," Milner said. "A lot of people choose to drink more iced tea because it is low in calories and tastes better than water. However, in terms of kidney stones, they might be doing themselves a disservice."
Though hot tea also contains oxalate, it's hard to drink enough to cause kidney stones, Milner said. About 85 percent of tea consumed in the United States is iced, according to the Tea Association of the USA.
Men are four times more likely to develop kidney stones than women, and the risk rises dramatically after age 40. Postmenopausal women with low estrogen levels and women who have had their ovaries removed also are at increased risk.
Kidney stones are small crystals that form from minerals and salt normally found in the urine in the kidneys or ureters, the small tubes that drain urine from the kidney to the bladder. Kidney stones usually are so small they are harmlessly expelled from the body. But stones sometimes grow large enough to become lodged in the ureters.
To quench thirst and properly hydrate, water is the best choice, Milner said. Real lemonade (not powdered) is another good option. "Lemons are high in citrates, which inhibit the growth of kidney stones," Milner said.
Milner advised that people at risk for kidney stones should cut back on foods that contain high concentrations of oxalates, such as spinach, chocolate, rhubarb and nuts. They should ease up on salt, eat meat sparingly, drink several glasses of water a day and eat foods that provide adequate amounts of calcium, which reduces the amount of oxalate the body absorbs.
Milner also advises that if you drink iced tea and have kidney stones, ask your specialist if the drink could be a contributing factor. (Patients aren't always asked.) If so, it is relatively easy to check if you are producing too many oxalates.
"Like many people, I enjoy drinking iced tea in the summer," Milner said. "But don't overdo it. As with so many things involving a healthy lifestyle, moderation is the key."