Exposure to fine particulate air pollution appeared to be associated with an increased risk for chronic kidney disease (CKD) and progression to end-stage renal disease (ESRD), according to a newly published epidemiologic study involving close to 2.5 million U.S. veterans followed for approximately 8 years.
The study, published online in the Journal of the American Society of Nephrology, relied on air pollution data from the Environmental Protection Agency (EPA) and NASA satellites and showed a linear relationship between fine particulate matter exposure and risk of kidney function decline and kidney disease.
Based on the analysis, the researchers estimated that about 45,000 new cases of kidney disease and 2,400 new cases of kidney failure each year can be attributed to particulate matter air pollution exposures exceeding the level the EPA considers safe.
Nephrologist Ziyad Al-Aly, MD, of the Veterans Affairs Saint Louis Health Care System, who led the study, told MedPage Today that air pollution exposure may play a significant role in the rising incidence of kidney disease that is not able to be explained by comorbidities such as high blood pressure and diabetes.
“Hypertension and diabetes are major risk factors for kidney disease, but there has been a surge of cases among people without hypertension or diabetes, and this phenomenon is very common in areas with high pollution. We think this might explain some of the burden of kidney disease that has no known cause.”
Air pollution, especially fine particulate matter <2.5 µm in aerodynamic diameter (PM2.5), is a well-established risk factor for heart disease, respiratory disease, and death. But Al-Aly said few previous studies have examined the potential impact of PM2.5 on kidney function in humans.
He noted that laboratory studies have linked exposure to deep exhaust particles of 2.5 micrometers and smaller to renal injury in mice. Higher mortality from kidney disease has also been identified in the coal mining regions of Appalachia.
The study is the first large epidemiologic analysis to examine the possible impact of PM2.5 exposure on the development of chronic kidney disease and the progression of kidney disease.
The researchers linked EPA and Department of Veterans Affairs databases to build an observational cohort of 2,482,737 U.S. veterans, and used survival models to evaluate the association of PM2.5 concentrations and risk of incident estimated glomerular filtration rate (eGFR) <60 ml/min per 1.73 m2, incident CKD, eGFR decline ≥30%, and ESRD over a median follow-up of 8.52 years.
County-level exposure was defined at baseline as the annual average PM2.5 concentrations in 2004, and separately as time-varying, where it was updated annually and as cohort participants moved.
The researchers also examined PM2.5 estimates derived from NASA satellite sensors as an alternative data source to define ambient PM2.5 exposure levels.
Analyses of baseline exposures (median, 11.8 [interquartile range, 10.1–13.7] µg/m3), showed a 10-mg/m3 increase in PM2.5 concentration to be associated with increased risk of eGFR <60 ml/min per 1.73 m2 (HR, 1.21; 95% CI, 1.14-1.29), CKD (HR, 1.27; 95% CI, 1.17-1.38), eGFR decline ≥30% (HR, 1.28; 95% CI, 1.18-1.39), and ESRD (HR, 1.26; 95% CI, 1.17-1.35).
Time-varying analyses revealed that a 10-mg/m3 increase in PM2.5 concentration was associated with a similarly increased risk of eGFR <60 ml/min per 1.73 m2, CKD, eGFR decline ≥30%, and ESRD. Spline analyses showed a linear relationship between PM2.5 concentrations and risk of kidney outcomes.
NASA-derived satellite data showed similar results.
“The results were robust in sensitivity analyses including the estimation of different distance thresholds from an air-monitoring station (30, 10, and 5 miles), and analyses evaluating the association within metropolitan areas,” the researchers wrote. “The constellation of findings suggests that chronic exposure to fine particulate matter air pollution is a significant risk factor for the development and progression of kidney disease.”
Al-Aly said this makes sense, because fine particulate matter air pollution of <2.5 µm in diameter permeates lung tissue following inhalation and enters the blood stream: “Human kidneys filter as much as 45 gallons of blood a day. They may be especially susceptible to the harmful effects of particulate matter in the blood.”
Funding support for the study was provided by the U.S. Department of Veterans Affairs.
Al-Aly and co-authors reported having no relevant relationships with industry related to the study.
F. Perry Wilson, MD, MSCE Assistant Professor, Section of Nephrology, Yale School of Medicine and Dorothy Caputo, MA, BSN, RN, Nurse Planner