Global warming may expand U.S. 'kidney stone belt', say scientists

OTTAWA - One of the first direct impacts that global warming has on our health may hit us where it hurts: In the kidneys.

People will develop more kidney stones in a hotter climate, because the heat tends to make us dehydrated and that causes the stones to form, two Texas urologists say.

Drs. Margaret Peale and Yair Lotan of the University of Texas say there's already a "kidney stone belt" in the hot, humid U.S. southeast, stretching from Louisiana to Florida and north to Tennessee.
Expect that belt to move north with the warmer climate, increasing kidney stone rates outside today's belt by 30 per cent by 2050, they say in a paper published today in Proceedings of the National Academy of Sciences.

The study doesn't cover Canada, but it suggests changes coming close to our doorstep. Of two computer models used in their study, one predicts most of the increase will come in central states such as Kentucky and Kansas. But the other forecasts a greater increase in states bordering Canada such as Ohio and Pennsylvania, and the U.S. Eastern seaboard generally.

Wherever the greatest effect happens, both models agree the kidney stone belt will expand northwards, approaching Canada, in some way.

The study worked by comparing the rate of kidney stones reported in different geographic regions, and comparing these with temperature records by region. From there the team looked at forecasts of how the U.S. climate is likely to change by the year 2050.

Kidney stones are a common ailment. They affect roughly one in 10 men in North America over a lifetime, though fewer women.

Normally, urine carries waste chemicals out of the body. But people who become dehydrated in hot weather have trouble producing enough urine to do the job.

Mineral salts left behind can form solid crystals in the kidneys, and eventually these can develop into painful "stones."

The link between temperature and kidney stones is well known, Peale said.

"When people relocate from areas of moderate temperature to areas with warmer climates, a rapid increase in stone risk has been observed. This has been shown in military deployments to the Middle East for instance."

It's the second recent piece of bad medical news for people in the U.S. Southeast.

In June, researchers reported that this area is also a "stroke belt," where the risk of stroke is about 10 per cent higher than in other regions, and even visiting increases the risk of a fatal stroke.