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Doctors say that hotter weather is linked with everybody's favorite cause of blood in the urine, and that kids could be most affected.

When one thinks of the warming climate, the phrases that pop into mind probably aren't "nausea and vomiting," "sharp, stabbing pain," and "blood in your urine." Yet these awful symptoms could become more prolific in the coming decades, as hotter weather appears to be linked with the risk of growing a kidney stone.

This disheartening prognosis comes from doctors at the Children's Hospital of Philadelphia and elsewhere who've completed a seven-year-long study of 60,433 patients in several major U.S. cities. When the temperature goes up, there's a subsequent spike in the number of people visiting hospitals for stone issues, they write in Environmental Health Perspectives. According to lead author Gregory E. Tasian: "We found that as daily temperatures rise, there is a rapid increase in the probability of patients presenting over the next 20 days with kidney stones."

The researchers found this correlation to exist in cities with disparate climates, including Atlanta, Chicago, Dallas, and Philadelphia—though it was not present in Los Angeles. They believe that a crucial predictor of kidney-stone risk is the number of "hot" days a city experiences, ones with mean daily temperatures above 81 degrees rather than the city's annual mean temperature. They found that Atlanta and Los Angeles both have mean annual temperatures of 63 degrees but that stones were twice as common in Atlanta, which has more hot days.

What could account for this painful parallel? For one, more sweltering temperatures may be dehydrating people, causing the kind of mineral build-up in their urine that helps kidney stones form. Stones have been known to grow in as short a period as three months; however, Tasian's team found a much shorter link of three to 20 days between when daily temperatures peaked and patients sought medical assistance en masse for stones. They say that this quicker-than-expected association raises "questions about the rate at which kidney stones might develop in vivo."

The researchers caution that any future increase in kidney stones is likely to hit people already medically predisposed to them (for instance, those with Randall’s plaques). Though stones are responsible for about half a million visits to the emergency room each year, only 11 percent of the U.S. population has developed them.

There's been a worldwide rise in kidney stones over the last three decades, especially among children. The reason for their spreading prevalence is still unknown. Some surmise it has to do with changes in diet and fluid consumption. Perhaps it also relates to the scourge of heat that's marked the planet's recent climate, the researchers write:

The study's broader context is in patterns of global warming. The authors note that other scientists have reported that overall global temperatures between 2000 and 2009 were higher than 82 percent of temperatures over the past 11,300 years. Furthermore, increases in greenhouse gas emissions are projected to raise earth's average temperatures by 2 to 8 [degrees] F (1 to 4.5 C) by 2100. "Kidney stone prevalence has already been on the rise over the last 30 years, and we can expect this trend to continue, both in greater numbers and over a broader geographic area, as daily temperatures increase," concluded Tasian. "With some experts predicting that extreme temperatures will become the norm in 30 years, children will bear the brunt of climate change."

Top image: Atelier_A/Shutterstock.com

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