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The Deadly Consequences of Fine Particle Air Pollution

PM2.5-associated lung cancer deaths by state.

A new study finds an association between fine particulate matter (PM2.5) air pollution and deaths from nine different causes, including cardiovascular disease, cerebrovascular disease, hypertension, dementia, and lung cancer, among others. Furthermore, 99% of PM2.5-associated deaths were linked to levels of PM2.5 exposure currently deemed acceptable by US Environmental Protection Agency (EPA) recommendations.

Atmospheric particulate matter with a diameter of less than 2.5 micrometers, PM2.5, is produced by various types of combustion, with sources including motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, and some industrial activity. It is "associated with increased risk of several causes of death," write the researchers in their study, published today in JAMA Network Open. "However, epidemiologic evidence suggests that current knowledge does not comprehensively capture all causes of death associated with PM2.5 exposure."

Seeking to remedy this knowledge gap, the investigators followed a cohort of 4,522,160 US veterans for a median of 10 years. Study participants were 93.8% male, with a median age of 64.1 years. Of the participants, 82.0% were white, 14.8% were black, and 3.2% were of other races. Participants were selected from among individuals who received care in the Veterans Affairs (VA) health system during the year 2006. Eligible participants were those whose location of residence was known, who could be linked at baseline to a PM2.5 exposure level, and for whom regional data was available on population density, County Health Rankings, and the 2013 Area Deprivation Index (ADI), a ranking of socioeconomic status disadvantage calculated for a given geographic region using measures of education, employment, housing quality, and poverty.

During the 10-year follow-up period, there were a total of 1,647,071 deaths, comprising 36.4% of the study population. Following adjustments for the personal characteristics of age, race, sex, and smoking status as well as the regional characteristics of population density, ADI, rurality, extent of access to healthy food or exercise opportunities, and prevalence of excessive drinking, PM2.5 was associated with 197,905.1 deaths due to nonaccidental causes, including 188,540.3 deaths due to noncommunicable diseases, with estimated age-standardized death rates per 100,000 persons of 51.4 for nonaccidental causes and 48.4 for noncommunicable diseases.

In their calculations of deaths due to specific causes, the researchers found that exposure to PM2.5 was associated with 56,070.1 deaths from cardiovascular disease; 40,466.1 deaths from cerebrovascular disease; 30,696.9 deaths from hypertension; 19,851.5 deaths from dementia; 17,545.3 deaths from lung cancer; 8,854.9 deaths from pneumonia; 7,175.2 deaths from chronic kidney disease; 645.7 deaths from chronic obstructive pulmonary disease (COPD); and 501.3 deaths from type 2 diabetes. These findings confirm previously known associations between PM2.5 and cardiovascular disease, cerebrovascular disease, lung cancer, pneumonia, COPD, and diabetes, and they expand that list to include associations with hypertension, dementia, and chronic kidney disease.

Age-standardized death rates were highest among non-Hispanic black or African American individuals, and age-standardized death rates due to both nonaccidental causes and noncommunicable diseases correlated with increasing poverty as measured by the ADI. In addition, deaths due to both nonaccidental causes and noncommunicable diseases varied by region, clustering in portions of the Midwest, Appalachia, and the South.

"Profound racial and socioeconomic disparities in PM2.5 exposure are well documented," write the researchers, led by first author Benjamin Bowe, MPH, doctoral candidate in Epidemiology and Biostatistics at St. Louis University, and senior author Ziyad Al-Aly, MD, Director of the Clinical Epidemiology Center and Chief of Research and Education Service at Veterans Affairs St. Louis Health Care System. "Our formal interaction analyses provide evidence suggesting that for the same level of PM2.5 exposure, black individuals and those living in disadvantaged communities (areas of high ADI) are more vulnerable… to the adverse health outcomes associated with PM2.5 exposure, further compounding their risk. Greater attention is needed to address and alleviate the burden borne by racial monitories and those living in disadvantaged communities who might also be least equipped to deal with the adverse health consequences of air pollution."

The investigators found that 99.0% of PM2.5-associated deaths from nonaccidental causes and 99.0% of the deaths from noncommunicable diseases were linked with PM2.5 exposure beneath the annual average level of 12 µg/m3 that the EPA recommends as the maximum PM2.5 exposure.

"An extensive body of scientific evidence suggests substantial health gains realized by cleaner air and that further reduction in PM2.5 might lead to even greater reduction in burden of disease," write Mr. Bowe and colleagues. "Our results further inform this national discussion, [suggesting] increased risk across the full PM2.5 range between the theoretical minimum risk exposure level and 12 μg/m3."

The fact that 99% of PM2.5-associated deaths occurred at levels beneath the EPA recommendation "reflects a near total elimination of death burden associated with PM2.5 concentrations above 12 μg/m3, a testament to the remarkable progress in cleaning the air and meeting the current EPA standards," note the researchers, "but also indicates that further reduction in PM2.5 concentrations below the current EPA standards may yield additional public health benefit."

For More Information

Bowe B, Xie Y, Yan Y & Al-Aly Z (2019). Burden of cause-specific mortality associated with PM2.5 air pollution in the United States. JAMA Netw Open. [Epub ahead of print] DOI:10.1001/jamanetworkopen.2019.15834

Image Credit: © Benjamin Bowe et al, JAMA Network Open. Licensed under CC-BY 4.0

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