A new study of 60 million Americans—about 97% of people age 65 and older in the United States—finds that long-term exposure to airborne fine particulate matter (PM2.5) and ozone increases the risk of premature death, even when that exposure is at levels below the National Ambient Air Quality Standards (NAAQS) currently established by the US Environmental Protection Agency. The study is published in the New England Journal of Medicine.
The Harvard T.H. Chan School of Public Health researchers found that men, blacks, and low-income populations had higher risk estimates from PM2.5 exposure compared with the national average, with blacks having mortality risks three times higher than the national average.
Increases of 10 μg per cubic meter in PM2.5 and of 10 ppb in ozone were associated with increases in all-cause mortality of 7.3% (95% confidence interval [CI], 7.1 to 7.5) and 1.1% (95% CI, 1.0 to 1.2), respectively.
When the analysis was restricted to person-years with exposure to PM2.5 of less than 12 μg per cubic meter and ozone of less than 50 ppb, the same increases in PM2.5 and ozone were associated with increases in the risk of death of 13.6% (95% CI, 13.1 to 14.1) and 1.0% (95% CI, 0.9 to 1.1), respectively.
The results showed that if the level of PM2.5 could be lowered by just 1 microgram per cubic meter (ug/m3) nationwide, about 12,000 lives could be saved every year. Similarly, if the level of ozone could be lowered by just 1 part per billion (ppb) nationwide, about 1,900 lives would be saved each year.
This is a study of unprecedented statistical power because of the massive size of the study population. These findings suggest that lowering the NAAQS for fine particulate matter will produce important public health benefits, especially among self-identified racial minorities and people with low incomes.—Francesca Dominici, principal investigator, professor of biostatistics at Harvard Chan School and co-director of the Harvard Data Science Initiative
The researchers examined Medicare claims records of 60 million Americans 65+ over a seven-year period, representing 460 million person-years of follow-up. They also estimated air pollution levels at each 1 kilometer grid for the entire US upon which the claims data could be overlaid and interpreted.
To do this, the Harvard Chan researchers leveraged the results of an exposure prediction model developed by doctoral student Qian Di and Joel Schwartz, professor of environmental epidemiology and the study’s senior author. The exposure prediction model leverages satellite-based measurements and a computer simulation of air pollution.
By relying on this well-validated prediction model, the team was able to include subjects who live in unmonitored and less-populated areas so that the effects of air pollution on all 60 million people could be analyzed regardless of whether they lived in urban, suburban, or rural areas.
This study shows that although we think air quality in the United States is good enough to protect our citizens, in fact we need to lower pollution levels even further.—Joel Schwartz
Support for the study came from grants from the Health Effects Institute (4953-RFA14-3/16-4), National Institutes of Health (R01 ES024332-01A1, ES-000002, ES024012, R01ES026217), National Cancer Institute (R35CA197449), and Environmental Protection Agency (83587201-0, RD-83479801).
Qian Di, Yan Wang, Antonella Zanobetti, Yun Wang, Petros Koutrakis, Christine Choirat, Francesca Dominici, Joel D. Schwartz (2017) “Air Pollution and Mortality in the Entire Medicare Population” New England Journal of Medicine doi: 10.1056/NEJMoa1702747