Air pollution has been recognized as a global health burden, but epidemiologic studies on the effects of long-term exposure to ozone (O3) have been inconclusive. Moreover, studies on the effects of O3 on renal outcomes and mortality in chronic kidney disease (CKD) are lacking. To address the absence of data, Ejin Kim and other researchers examined the effects of ozone on the risk of end-stage renal disease (ESRD) and mortality in a two-pollutant model adjusted for socioeconomic status. The results appeared in BMC Nephrology.
Study data came from 61,073 patients with CKD who visited one of three hospitals in Seoul, South Korea, between January 2001 and December 2016. Enrolled patients met the definition of CKD as outlined in the 2012 Kidney Disease Improving Global Outcomes Clinical Practice Guideline for the Evaluation and Management of CKD report and had functional and/or structural damage to the kidneys lasting more than 3 months. To examine ozone’s effects on individuals, the researchers included data from nationwide and district disease surveillance.
The cohort included 56,470 participants aged 58.37 ± 17.37 years with an estimated glomerular filtration rate (eGFR) of 61.07 ± 29.92 mL/min/1.73m2; 29,961 of the participants were male (48.82%). In addition, 23.06% of patients were diagnosed with diabetes mellitus, 21.85% had hypertension, 29.42% had CKD stage 3, and 16.79% had advanced CKD with GFR less than 30 mL/min/1.73m2.
The researchers obtained hourly O3 concentrations from 533 air quality monitors between 2001 and 2016. They defined ozone concentration in terms of moving 8-hour averages (the average value of the 8-hour maximum O3 concentration on a given day). During the study period, the mean concentrations of O3 were 31.2 ppb. The time-series plot showed the national average daily 8-hour maximum O3 concentration; there were days when air quality standard O3 concentrations (60 ppb for each 8-hour average) were exceeded. The researchers divided personal exposure into two separate methods, one assigned to the individual’s city, county, and district administrative entities according to their place of residence and the other using their address data to determine latitude and longitude coordinates. Researchers then determined personal exposure using the inverse distance weighting method.
The study outcome was cause-specific mortality and incidence of ESRD. During the study period, there were 5957 cases of ESRD and 6768 deaths. The researchers found that in both the district and individual-address models, the moving O3 average was associated with an increased risk of ESRD and all-cause mortality. To adjust for the potential effects of other measured pollutants, the research team used a two-pollutant model. However, associations between O3 exposure and study outcomes remained significant even after adjusting for nitrogen dioxide. The hazard ratio (HR) value for the district-level assessment was 1.025 (95% CI, 1.014-1.035); the HR value for the point-level assessment was 1.040 (95% CI, 1.035-1.045).
For the impact of ozone on ESRD, HR values were 1.049 (95% CI, 1.044-1.054) at the district level and 1.040 (95% CI, 1.031-1.050) at the individual address of the exposure assessment. The ozone HR for all-cause mortality was 1.012 (95% CI, 1.008-1.017) for administrative districts and 1.040 (95% CI, 1.031-1.050) for individual addresses.
In the district allocation model, the moving O3 average for 365 days was associated with a higher risk of ESRD (HR, 1.034; 95% CI,1.031-1.036) and all-cause mortality (HR, 1.020; 95% CI, 1.018-1.023). This was also true in the point-allocation model for ESRD risk (HR, 1.019; 95% CI, 1.011-1.026) and all-cause mortality (HR, 1.047; 95% CI, 1.041-1.054).
The authors noted a few limitations of the study. Measurement error likely occurred due to the use of zip codes rather than the exact house address or place of death of each participant to determine exposure level. Selection bias may have resulted from most participants being in a specific metropolitan area. Data used in the study were at least 4 years old, so exposures and outcomes may not match current data. Finally, there was limited direct usage in model fitting due to the lack of information in the researchers’ data that might correct for the lifestyle choices and health condition of patients with CKD.
“In conclusion,” the authors wrote, “based on a large cohort of participants with CKD, long-term exposure to O3 is associated with an increased risk of ESRD and mortality. Our findings highlight the need for better measures to control O3 exposure and the emission of pollutants that contribute to the increase of O3 in the atmosphere.”
Source: BMC Nephrology
© 2025 Mashup Media, LLC, a Formedics Property. All Rights Reserved.