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Global warming to spark rise in kidney stone cases, study says

By Jeremy Manier

Chicago Tribune

It may not be the most profound effect of global warming, but it could be the most painful: Climate change could bring a sharp increase in cases of kidney stones in Illinois and other Midwestern states, according to a new study.

Linking climate change to kidney stones seems odd, but it’s based on the solid medical finding that people in warm regions develop the condition at increased rates. Sweating in warm weather removes fluid from the body and increases the salt concentration in urine, which can spur the growth of kidney stones.

By the year 2050, the new report estimates that a large chunk of Illinois will fall within America’s "kidney-stone belt," which currently includes only Southern states. The Chicago area alone would see up to 100,000 extra cases each year, according to the report published Monday in a widely respected journal, Proceedings of the National Academy of Sciences.

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That sort of medical chain reaction may barely hint at the looming public health threat of global warming, researchers say. The federal Centers for Disease Control and Prevention has warned that higher temperatures could bring more lethal heat waves, more blooms of algae that infect fish with toxins, and the easier spread of some insect-borne illnesses such as Lyme disease and Rocky Mountain spotted fever.

"Climate change’s impact on public health will be broad, severe and affect all sectors of the public health system," said George Luber, associate director for climate change at the CDC’s national center for environmental health.

The effects also could be expensive. The authors of Monday’s study estimate that the extra kidney stone cases would cost an additional $1 billion each year to treat.

Counteracting the effects of temperature may be as simple as having people drink more water. But doctors said getting an entire region of the country to change drinking habits could prove difficult.

Most climate researchers believe emissions of carbon dioxide and other greenhouse gases are raising average temperatures worldwide and that North America will see a rise of at least 2 degrees Fahrenheit in the 21st Century. The new study, by researchers at the University of Texas at Dallas and the University of Texas Southwestern Medical School, combined medical studies of how regional temperature affects kidney stones with climate forecasts by the Intergovernmental Panel on Climate Change.

The effect of temperature on kidney-stone formation is a fundamental teaching of urology, said Dr. Mark Litwin, a professor of urology and public health at UCLA. He said the Texas team’s blending of that physiological fact with climate data was "flawless."

"This should be a wake-up call," Litwin said.

Kidney stones pose an unusual public health challenge. Rarely fatal, they nonetheless create one of the most painful medical conditions--in some cases more excruciating than childbirth, according to some victims.

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Larry Gunn’s doctors discovered his large kidney stone--more than half an inch wide--in the course of his treatment for cancer two years ago. It cut his kidney function by 80 percent and brought on night sweats so bad that he would change his shirt three times during the night.

"It was just like someone was twisting a knife in me," said Gunn, 66, a part-time truck driver from Hampshire.

Such stones form when salts and minerals collect into crystals in the kidneys, sometimes in a matter of days. Sometimes, the crystals form spiky masses that are almost impossible to pass through normal urination.

"It’s the kind of pain that brings you to your knees," said Dr. John Milner, a urologist at Loyola University Medical Center, who treated Gunn.

The most common treatments for kidney stones include blasting the object with shock waves produced by pulses of sound or threading a tube to the stone and destroying it with a small laser.

Researchers have known for years that cases of kidney stones peak soon after the hottest summer months and that people in warm climates are at added risk. The dehydration that often comes from sweating means there’s less fluid to dilute the salts in urine, which can more easily clump together into crystals.

"It’s just like rock candy precipitating out of a glass of sugar water," said Litwin of UCLA.

More than 5 percent of the U.S. population has kidney stones, accounting for about half a million emergency room visits each year, according to federal estimates. Treatment costs range from about $8,000 for most noninvasive techniques to $50,000 or more when patients need surgery.

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The new study predicts about 2.2 million additional climate-related kidney stone cases each year by 2050.

The project brought together kidney researchers from the University of Texas Southwestern Medical School with Tom Brikowski, a geologist and climate change specialist at the University of Texas at Dallas. The team devised two mathematical models of how kidney-stone cases would respond to increasing temperatures, and in each one the Midwest wound up with far more cases than today, Brikowski said. Although Chicago would not technically be part of the kidney-stone belt, where cases are 20 percent higher than in the Northeast, the metro region would see a significant rise under either model.

"This is definitely something to pay attention to in Chicago," he said.

No one expects a kidney-stone catastrophe. At worst, the rates here would simply rise to what doctors already see in most Southern states. But experts said the problem offers a glimpse at a future in which the effects of climate change may be difficult to predict.

An outbreak of fish poisoning that hit St. Louis and Washington, D.C., last year showed how seemingly subtle climate-related changes can have tangible health effects, said the CDC’s Luber. The poisoning involved tropical fish tainted with the ciguatera toxin, which comes from a type of algae that previously was not found north of the central Gulf of Mexico. The tainted fish came from the northwest corner of the gulf, suggesting the habitat had warmed enough for the algae to thrive there, Luber said.

Kidney stones may be easier to prevent than most of the health threats from climate change. Milner of Loyola said he advises his high-risk patients to stop adding salt to food and to drink two extra glasses of water each day.

"It’s hard for people to stay up on their water, but you have to do it religiously," Milner said.

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