Decades of research show that air pollution harms the heart and lungs and increases the risk of death. These findings have led to regulations that reduce air pollution and improve health. Yet even with these improvements, scientists continue to discover effects on health outcomes, including asthma, autism, and others. These were some of the topics discussed during the Dec. 5-8 NIEHS Environmental Health Sciences (EHS) FEST, in Durham, North Carolina.
In the opening plenary session, Joel Kaufman, M.D., of the University of Washington mentioned that substantial epidemiological evidence links air pollution (see sidebar) with cardiovascular disease, especially heart attacks and strokes, and toxicological studies explain the underlying biological mechanisms. He said it is also clear that air pollution affects asthma and reduces lung growth in children, and recent studies suggest air pollution damages cognitive function and birth outcomes.
“We’ve shown that if you reduce air pollution, you can show immediate health benefits, especially on reduced cardiovascular events,” said Douglas Dockery, Sc.D., director of the Harvard-NIEHS Center for Environmental Health. “We’ve seen major improvements in U.S. air quality, but there are still hotspots and local exposures, for example, from roadways and industrial facilities, that are begging for intervention.”
The legacy of the Harvard Six Cities study
Dockery has spent decades working on the NIEHS-funded Harvard Six Cities study, highlighted during an EHS FEST session titled “Leading the Way: From Harvard Six Cities Study to Global Environmental Health.” The study was established in 1974 to compare health in cities with high (St. Louis, Missouri, and Steubenville, Ohio), medium (Harriman, Tennessee, and Watertown, Massachusetts), and low (Portage, Wisconsin, and Topeka, Kansas) levels of air pollution.
A seminal paper from the study found that fine particulate matter was largely responsible for the link between air pollution levels and increased mortality rates. Fine particles, generated mainly by fossil fuel combustion, are less than 2.5 micrometers in diameter and can be inhaled deep into the lungs. According to Sri Nadadur, Ph.D., program officer in the NIEHS Exposure, Response, and Technology branch, this and additional findings from larger cohorts of the American Cancer Society study were major contributors to the establishment of the U.S. Environmental Protection Agency standard for fine particulate matter in 1997.
These and other air quality improvements have led to better lung development in children, according to findings from the NIEHS-funded Children’s Health Study (CHS) at the University of Southern California (USC). The CHS also showed that bronchitis-related symptoms like cough and phlegm in children vary from year to year with air pollution levels.
“The CHS is one of the many legacies of the Six Cities study,” said Rob McConnell, M.D., of USC.
Air pollution worsens, and may cause, asthma
According to McConnell, scientists generally agree that air pollution worsens asthma, but does not actually cause the disease. He said this conclusion is based on the lack of a consistent pattern in air pollution levels and asthma rates when scientists compare study results across communities. However, McConnell pointed out that if looking within communities, for example, at differences in asthma rates based on how close to roadways children live, a different story emerges.
“Many studies in the U.S. and Europe show that living near busy roads and freeways is linked to asthma,” said McConnell. “There is not universal consensus, but I think there’s an emerging consensus that near-roadway pollution causes asthma.”
Air pollution may affect brain development and decline
Introducing a session on emerging research topics, Heather Volk, Ph.D., of Johns Hopkins University, said that studies of respiratory and cardiovascular health are continuing.
At the same time, air pollution researchers are studying effects on brain development, cognitive decline, obesity, and even infectious outcomes like tuberculosis. “Even though air quality is getting better, we are still demonstrating health effects, so there is still work to be done,” she said.
Connections between exposure to air pollution and autism diagnosis have been demonstrated in more than 12 epidemiologic studies, according to Deborah Cory-Slechta, Ph.D., of the University of Rochester Medical Center. She observed notable changes in the brains of mice exposed to ultrafine particulate matter, or particles that are less than 0.1 micrometers in diameter, which may help to explain this link.
“We’re very early in these studies of the brain. But as somebody who came from the world of lead exposure in children, I was astounded at what I was seeing, and wondered whether this was the next lead,” said Cory-Slechta.
(Virginia Guidry, Ph.D., is a technical writer and public information specialist in the NIEHS Office of Communications and Public Liaison, and a regular contributor to the Environmental Factor.)