Global warming may turn out to be more than just a pain in the neck: Rising average temperatures might trigger an increased prevalence of kidney stones.

About 12 percent of men and 7 percent of women in the United States will be stricken during their lifetime with symptoms of a kidney stone, which forms when minerals dissolved in urine crystallize somewhere in the kidney or urinary tract.

One of the primary causes of these painful deposits is low urine volume, brought about either by low fluid intake or by increased fluid loss, says Margaret S. Pearle, a urologist at the University of Texas Southwestern Medical Center at Dallas.

Although people in all parts of the nation can suffer kidney stones, the ailment is much more common in some regions than in others.

Prevalence of stones in the Southeast is as much as 50 percent higher than it is the Northwest, Pearle says. Urologists have long known of a “kidney stone belt,” which stretches from the Carolinas through Texas to southern and central California, she notes.

Overall, differences in average annual temperature among various U.S. regions account for about 70 percent of the variation in kidney stone prevalence. Dramatic increases in the ailment among soldiers deployed to arid regions, as well as seasonal variations in frequency of the malady, bolster the link between temperature and prevalence, the researchers propose.

Now, in the July 15 Proceedings of the National Academy of Sciences, Pearle and her colleagues estimate how the prevalence of kidney stones — and the costs needed to treat them — might increase as climate change boosts average temperatures.

In one climate change scenario —in which the atmospheric concentrations of carbon dioxide rise to 850 parts per million by 2100, up from about 380 ppm today — average annual temperature in some parts of the United States would rise as much as 3.25 degrees Celsius, says Tom H. Brikowski, a hydrologist at the University of Texas at Dallas and coauthor of the paper.

Under such a scenario, kidney stone prevalence will undoubtedly rise. However, Pearle notes, the specific relation between average annual temperature and prevalence isn’t clear. While some urologists suggest that an increase in temperature will lead to a proportional increase in kidney stone prevalence, others propose that above a certain temperature threshold — say, 15° C — the risk of developing stones doesn’t increase.

In the model where the risk of stones rises proportionally with an increase in average annual temperature, the largest bumps in kidney stone cases by the year 2050 are concentrated in California, Texas, Florida and the East Coast, the researchers report. Under the other model, the increase in kidney stone prevalence over that period would be largely confined to Northern California and a swath running from Kansas to Virginia, because the average annual temperature in much of the Southeast already sits above 15° C. In some regions, kidney stone prevalence could rise about 30 percent, the analysis suggests.

Between now and 2050, climate change could cause an additional 1.6 million to 2.2 million cases of kidney stones, the researchers speculate. At that time, annual medical costs for stone-related emergency room visits, out-patient appointments and surgery would run between 900 million and 1.3 billion year-2000 dollars, the researchers estimate.

“These costs are pretty staggering,” says Anthony Smith, a urologist at the University of New Mexico in Albuquerque. He describes the new research as “a fascinating study … that indicates climate-related changes in the environment will have large economic and human costs.”

The new research “is really a seminal piece of work,” says Mark S. Litwin, a urologist at the University of California, Los Angeles. Kidney stones are one of the largely unrecognized — and largely preventable — consequences of climate change, he adds.

More aggressive efforts to maximize hydration could result in a decreased incidence of stone problems, says Ira Sharlip, a urologist in San Francisco.

Litwin agrees: “The irony is, the cure is fairly simple,” he notes. “Just drink more water.”

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