Climate-related increase in the prevalence of urolithiasis in the United States

Abstract

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.

Fig. 1.

Temperature-dependence models for nephrolithiasis risk relative to the Northeast (Upper) and current and projected MAT for U.S. climate divisions (Lower). Linear model 80% prediction interval and non-linear model 95% confidence interval is shown by shading. Original VA data were grouped by U.S. census region, temperature is the value for nearest corresponding National Oceanic and Atmospheric Administration (NOAA) climate region. Nonlinear risk model [1983 data, age- and gender-corrected (3)] exhibits peaked temperature dependence. Heating will drive many climate divisions to higher risk of urolithiasis, regardless of choice of nephrolithiasis model.

Fig. 2.

Predicted warming and linear model nephrolithiasis risk change by 2050 for U.S. Strongest warming is in the midcontinent and upper Midwest. Heavy lines show the four U.S. census regions, and light gray lines show NOAA climate divisions.

Fig. 3.

Predicted growth in high-risk stone area (stone belt; risk ratio ≥1.2) vs. time, for 2000 (yellow), 2050 (orange), and 2095 (red); linear model. At 2000, 41% of the population is within a high-risk zone, 56% at 2050, and 70% at 2095, based on year 2000 population distribution.

Fig. 4.

Predicted changes in stone risk by 2050, nonlinear model (3). Peaked risk vs. temperature model (Fig. 1) concentrates risk change at northern edge of the present-day stone belt (yellow, Fig. 3). Trailing that to the south is a zone of reduced risk (green).

Fig. 5.

Impact of climate-related increase in nephrolithiasis prevalence by 2050 for the linear (a) and nonlinear (b) models. Data are represented as the number of new climate-related cases (predicted 2050 nephrolithiasis prevalence times 2050 estimated population).