Poor Air Quality Linked to CKD Risk

Could differences in air quality contribute to the observed regional variations in chronic kidney disease (CKD)? A study presented at Kidney Week 2014 finds a higher prevalence of recognized CKD in counties of the United States with higher particulate air pollution.

Epidemiologist Jennifer L. Bragg-Gresham, PhD, of the University of Michigan and colleagues evaluated differences in pollutant levels—specifically, fine particles smaller than 2.5 µm (PM2.5)—as potentially contributing to regional differences in CKD prevalence.

On the basis of Medicare claims data from 1.1 million persons aged 65 years and older, the prevalence of CKD by county ranged from zero to 60 percent, with a median of 16 percent. Associations between levels of PM2.5, determined from U.S. Environmental Protection Agency air-quality data made publicly available through the WONDER online database of the Centers for Disease Control and Prevention, and prevalence of recognized CKD in the Medicare data were analyzed.

“We found that poorer air quality was associated with a higher prevalence of CKD,” Bragg-Gresham and coauthors write. With PM2.5 treated as a continuous variable, each increment of 4 µg/m3 in PM2.5 was associated with a 3 percent higher CKD prevalence, after adjustment for individual-level confounders.

When counties were grouped by quartiles of PM2.5, a threshold at approximately14 µg/m3 was observed for higher CKD prevalence. This is much lower than the level typically considered unhealthy (40 µg/m3) for sensitive groups, such as children, the elderly, and people with cardiorespiratory disease.

Well recognized individual risk factors, such as age, diabetes, and hypertension explain some, but not all, of the wide regional variation in CKD prevalence. As yet unrecognized environmental factors, such as air pollution, might account for some part of the additional variability.

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Although observational studies cannot show causal relationships, this large cross-sectional study suggests that higher PM2.5 levels in a county are associated with higher rates of diagnosed CKD. The researchers call for further studies to clarify this relationship, including laboratory diagnosis of CKD, longitudinal designs, assessment of other air and environmental pollutants, and measures of individual pollutant exposure.

“If this association is borne out by future studies, it would have implications for reducing air pollution exposure for those with CKD and also for those at risk for the condition,” Bragg-Gresham said. “The potential public health significance of this finding is even greater for regions and countries with much higher levels of air pollution than the United States.”