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Stanford University School of Medicine

Kidney stones most likely to affect residents of warm, wet regions

Kidney stones are more common in warm, wet regions. Stanford urology resident Kai Dallas offers a possible explanation.

If you’ve ever had a kidney or bladder stone, you know how excruciating and debilitating it can be. The pain — typically felt in the abdomen, groin or back — is often severe enough to cause nausea and vomiting.

These stones are solid clumps of minerals and salts that form in the kidney or bladder when the urine becomes very concentrated, which allows minerals to crystalize and stick together. Factors that are known to increase the risk of stone formation include genetics, dehydration, a high-salt diet and obesity.

A landmark study published in 1994 determined that where you live also affects your risk for stone disease. U.S. residents in the south and the east have more stones than those in the west and north. What causes this geographic distribution? The answer is still unknown: weird, right?

One theory is that higher temperature is a risk factor, but Stanford urology resident Kai Dallas, MD, told me that temperature doesn’t fully explain the phenomena.

“If higher temperature alone was the primary driving factor, then the American Southwest should have an equally high prevalence rate to the Southeast. The fact that it does not suggests that there are additional factors at play,” explained Dallas.

So his research team explored a correlation between weather patterns and urinary stone prevalence in regions throughout California, by analyzing data on urinary stone operations from the California Office of Statewide Health Planning and Development and climate data from the National Oceanic and Atmospheric Administration.

Their study found that more urinary stone surgeries occurred in regions with more rain and higher temperatures. These results intrigued Dallas because "they explained an unanswered trend in the larger national trend.”

Further studies are needed to explore why exactly this association exists, but Dallas said he and his colleagues have a theory: “We hypothesize that the increased rate of stone burden in hot climates with higher precipitation could be related to the increased inefficiency of human body thermoregulation in wet heat verses dry heat. In other words sweating is less efficient in very humid hot conditions, causing further sweating and fluid loss. And dehydration has been shown to cause kidney stones.”

Dallas hopes their study results will lead to a greater understanding of the causes of stone disease and a better appropriation of resources to areas where the population faces a higher risk. He also explained that their findings are particularly important in light of climate change:

The Environmental Protection Agency predicts that global warming will increase global precipitation. In fact, in the contiguous 48 states, total annual precipitation has steadily increased 0.17 inches per decade since 1901. This means the whole United States climate will become hotter and wetter, which is exactly the climate patterns we found that places patients most at risk for kidney stone disease.

Previously: Geography may determine kidney failure treatment level and Study identifies socioeconomic and ethnic disparities for gallstone surgery
Photo by harryson

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