A Loyola University Medical Center urologist is warning those at risk for kidney stones to watch their intake of iced tea, a summertime favorite.

Iced tea contains high concentrations of oxalate, one of the key chemicals that lead to the formation of kidney stones, according to Dr. John Milner, assistant professor at Loyola University Chicago Stritch School of Medicine.

Kidney stones — small crystals that form from minerals and salt normally found in urine, the kidneys or ureters — are usually small enough to pass painlessly from the body. But stones sometimes grow large enough to become lodged in the ureters, which can be painful.

They are a common disorder of the urinary tract that affects about 10 percent of the population in the United States. 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.

Dehydration combined with increased iced tea consumption raises the risk of kidney stones, said Milner. 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. Hot tea also contains oxalate, but is not generally consumed in the same quantities, Milner said.

Other foods that contain high concentrations of oxalates include spinach, chocolate, rhubarb and nuts. Those at risk should reduce 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.

— Anne Aurand, The Bulletin