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Air pollution increases risk for death even at levels lower than federal standards

Short-term exposure to air pollution was associated with an increased risk for mortality in the U.S. Medicare population from 2000 to 2012, even at pollution levels below national air quality standards, according to findings recently published in JAMA.

“Several studies have provided evidence that short-term exposures to [fine particulate matter] and ozone were associated with mortality, but these studies primarily included large and well-monitored metropolitan areas,” Quan Di, MS, of the department of environmental health at the Harvard T.H. Chan School of Public Health and colleagues wrote.

Researchers noted that in 2012, the annual National Ambient Air Quality Standard for fine particulate matter was set to 12 g/m³ and the 24-hour standard was set to 35 g/m³. Although there is no annual standard for ozone, the 8-hour federal standard was set to 70 parts per billion. Di and colleagues examined more than 22.4 million case days and more than 76.1 control days involving the deaths of Medicare participants in the continental U.S. from 2000 throughout 2012, covering 39,182 zip codes. Smaller towns, cities and rural areas left out of previous studies were included this time.

They found that of all case and control days, 93.6% had fine particulate matter levels below 25 g/m³, and 95.2% of deaths occurred during these days. Also, 91.1% of days had ozone levels below 60 parts per billion, and 93.4% of deaths occurred during these days. In addition, the baseline daily mortality rates were 137.33 per 1 million persons at risk per day for the entire year and 129.44 per 1 million persons at risk per year for the warm season.

Further, researchers wrote that absolute risk differences in daily mortality rate were 1.42 (95% CI, 1.29-1.56) per 1 million persons at risk per day for each short-term increase of 10 g/m³ of fine particulate matter exposure (adjusted by ozone), and 0.66 (95% CI, 0.53-0.78) per 1 million persons at risk per day for each 10 parts per billion increase of warm-season ozone exposure (adjusted by fine particulate matter). The relative increases in mortality rate were 1.05% (95% CI, 0.95-1.15) and 0.51% (95% CI, 0.41-0.61) per day, respectively.

“There were no significant differences in the mortality risk associated with air pollution among individuals living in urban vs. rural areas,” Di and colleagues wrote. “This risk occurred at levels below current national air quality standards, suggesting that these standards may need to be reevaluated.”

In a related editorial, Junfeng Zhang, PhD, of the Duke Global Health Institute, wrote that to mitigate the risks caused by air pollution, individuals should minimize their outdoor activities when outdoor pollutants are expected to be higher, avoid places such as heavily polluted city streets, and, when feasible, place air pollutant monitors in residences and workplaces or wear devices that keep track of such conditions.

He added Di and colleagues’ findings suggest that the federal level of acceptable air pollution should be lowered.

“Some may argue that it would be too costly to make further improvements in air quality when pollution levels are relatively low. However, pollution controls required by the Clean

Air Act have been associated with preventing an estimated hundreds of thousands of premature deaths and with estimated economic benefits exceeding the costs,” he wrote.

“It can be assumed that even greater health benefits could result from further emission reductions, which can be achieved through cleaner energy production (eg, by renewable, nonpolluting sources such as wind and solar power) and a cleaner transportation fleet (eg, with electric and hybrid vehicles and low emission mass transportation).” - by Janel Miller

Disclosures : Di reports receiving grants from the NIH, Environmental Protection Agency, Health Effects Institute and the National Cancer Institute. Zhang reports receiving funding from Underwriters Laboratories to support a research project, serving as a member of an Environmental Protection Agency review panel and an honorarium for attending a global advisory board meeting on air pollution. Please see the study for the full list of the other authors’ relevant financial disclosures.