Nearly 66,000 early deaths would be prevented each year if U.S. air pollutant concentrations of three major contributors — fine particulate matter, ozone and nitrogen dioxide — were reduced from the 70th to the 60th percentile, according to a recent study led by a Harvard University researcher.
Published May 6 in Environmental Health, the results indicate a causal relationship between air pollution levels and mortality rate among the elderly — who are especially susceptible to severe outcomes from air pollutants — including at concentrations that meet Environmental Protection Agency standards.
The study data came from an existing Medicare cohort of 74 million beneficiaries age 65 and older between 2000-16, accounting for more than 95% of elderly people in the United States.
"Based on our findings, even at levels well below the national standards, [air pollutants] pose a considerable threat," lead author Yaguang Wei, a Ph.D. candidate at the Harvard T.H. Chan School of Public Health, told The Academic Times. "People are still dying from it."
According to Wei, current air pollution standards of government organizations such as the EPA do not adequately address the dangers of fine particulate matter, ozone and nitrogen dioxide.
"By reducing even a very small amount of pollutants, we can save thousands of lives," he said.
Fine particular matter, or PM2.5, was found to be the most harmful of the three pollutants studied, at the current air concentration of about 10 micrograms per cubic meter. The EPA's standard sets the accepted maximum level at 12 micrograms per cubic meter.
Another recent study found that short-term exposure to fine particulate matter could harm cognitive function in older men, including at concentrations not exceeding World Health Organization guidelines.
"Many studies have been focusing on PM2.5, which we found is the most harmful pollutant," Wei said. "However, much less attention [has been] paid to ozone and nitrogen dioxide — they deserve more attention."
Nitrogen dioxide is also well below the EPA standard but still poses a significant risk, according to the paper, and Wei noted that the EPA does not have any long-term standards for ozone.
"What we advocate is imposing a more rigorous standard for PM2.5 and NO2," Wei said. "And, establishing long-term ozone standards are absolutely necessary for better protecting our public health — especially among elders."
Fine particulate matter is microscopic particles that can be traced back to direct sources, such as construction sites, fires and even deep-fried foods. These particles can also be the product of airborne reactions with chemicals emitted from vehicles and power plants.
Generally, ozone comes from vehicle emissions as well, but can also stem from industrial pollution. Nitrogen dioxide, meanwhile, primarily comes from notorious fossil fuels, such as coal burned for energy.
When inhaled, all three can lead to symptoms including decreased lung function, coughing, asthma and other respiratory issues. PM2.5 is also known to cause an irregular heartbeat. And according to Wei, the greater the amount of these components in the air, the greater the risk of death — there is a clear causal relationship.
"We can directly predict the mortality risk at any air pollution level," he said. "Then, we can easily predict the number of early deaths that [are] caused — and could be saved — if the air pollution concentrations were reduced."
Such causal evidence is the preferred type to inform policymakers, Wei noted, meaning the study's results can be taken as proof that the current EPA standards are not strict enough, and also inform other countries' health regulations. For instance, the United Kingdom sets its PM2.5 limit at 25 micrograms per cubic meter.
To arrive at an accurate estimate of deaths caused by air pollution concentration levels, the team corrected for many variable factors, adjusting for sex, race, ethnicity, age, Medicaid eligibility, temperature and weather, among other things.
"We also adjust for community-level features," Wei said. "Population density in a community and median household income, education and smoking rates — we have done the best we can to adjust for all potential factors."
Still, there is room for error because it's very difficult to take precise measurements of air pollution levels due to rapid fluctuations and non-constant pollution distribution. Wei explained that even though the team used the most top-notch measurements available, which are widely used by other researchers and institutions, such measurements are still inaccurate, at least to some degree.
Going forward, the team says that to further correct for these measurements — and obtain a wider dataset and provide policymakers with additional evidence — studies should look at the whole population, not just elderly people. Such research may also inform about the mechanisms behind these air pollutants contributing to mortality rates. Looking within each population could also offer insight into the effects of different racial groups' exposure to air pollution levels.
"They will definitely affect the human health for young people," Wei stressed, noting that the level of causal harm is yet to be studied.
"We hope our study can provide some evidence for policymaking — not only for the U.S. EPA," he continued, "but also for the World Health Organization and others, with setting their air quality standards and estimating the health benefits of specific policies."
The study, "Emulating causal dose-response relations between air pollutants and mortality in the Medicare population," published May 6 in Environmental Health, was authored by Yaguang Wei, Francesca Dominici, Mahdieh Danesh Yazdi, Antonella Zanobetti and Joel Schwartz, Harvard T. H. Chan School of Public Health; Qian Di, Tsinghua University; and Weeberb J. Requia, Fundação Getúlio Vargas.