STONE DISEASE

Climate-related increase in the prevalence of urolithiasis in the United States
Brikowski TH, Lotan Y, Pearle MS
Geosciences Department, University of Texas at Dallas, Richardson, TX 75080-3021, USA
Proc Natl Acad Sci USA. 2008; 105: 9841-6

• An unanticipated result of global warming is the likely northward expansion of the present-day southeastern U.S. kidney stone “belt.” The fraction of the U.S. population living in high-risk zones for nephrolithiasis will grow from 40% in 2000 to 56% by 2050, and to 70% by 2095. Predictions based on a climate model of intermediate severity warming (SRESa1b) indicate a climate-related increase of 1.6-2.2 million lifetime cases of nephrolithiasis by 2050, representing up to a 30% increase in some climate divisions. Nationwide, the cost increase associated with this rise in nephrolithiasis would be $0.9-1.3 billion annually (year-2000 dollars), representing a 25% increase over current expenditures. The impact of these changes will be geographically concentrated, depending on the precise relationship between temperature and stone risk. Stone risk may abruptly increase at a threshold temperature (nonlinear model) or increase steadily with temperature change (linear model) or some combination thereof. The linear model predicts increases by 2050 that are concentrated in California, Texas, Florida, and the Eastern Seaboard; the nonlinear model predicts concentration in a geographic band stretching from Kansas to Kentucky and Northern California, immediately south of the threshold isotherm.
  
  
• Editorial Comment
  This novel study raises important concerns and provokes many unique avenues for future investigation. It is ironic that as the polar ice melts, and water levels rise, we may need this water to prevent kidney stone disease!
  In developed countries, we live in climate-control; ambient temperature set at 65 or 70 degrees F, irrespective of time of season. The health risk posed by rises in mean annual temperature (MAT) and heat index will be felt heaviest by those with occupations that demand a significant time outdoors (agriculture, construction etc.) The risks of global warming on stone formation will be more acutely felt by those living in areas not fortunate to have air-conditioning.
  The authors note that heat stress and heat index may have a closer link to the distribution of the stone belt than MAT. As scientists debate the “positive water vapor feedback” that links humidity with global warming, it will be important to consider this for stone risk projections. In addition, the interplay between vitamin-D metabolism, stone risk and atmospheric changes deserves further study.

Dr. Manoj Monga
Professor, Department of Urology
University of Minnesota
Edina, Minnesota, USA
E-mail: endourol@yahoo.com