Long-term exposure to ground-level ozone, a major component of smog, is associated with an increased risk of death from respiratory ailments, according to a new nationwide study led by a researcher at the University of California, Berkeley.
The study, to be published in the March 12 issue of the New England Journal of Medicine, analyzed the risk of death for both ozone and fine particulate matter, two of the most prevalent components of air pollution.
The study followed nearly 450,000 people for two decades and covered 96 metropolitan regions in the United States.
“This is the first time we’ve been able to connect chronic exposure to ozone, one of the most widespread pollutants in the world, with the risk of death, arguably the most important outcome in health impact studies used to justify air quality regulations,” said study lead author Michael Jerrett, UC Berkeley associate professor of environmental health sciences.
“Previous research has connected short-term or acute ozone exposure to impaired lung function, aggravated asthma symptoms, increased emergency room visits and hospitalizations, but the impact of long-term exposure to ozone on mortality had not been pinned down until now.”
The study found that for every 10 parts-per-billion (ppb) increase in ozone level, there is a 4 percent increase in risk of death from respiratory causes, primarily pneumonia and chronic obstructive pulmonary disease.
“World Health Organization data indicate that about 240,000 people die each year from respiratory causes in the United States,” said Jerrett. “Even a 4 percent increase can translate into thousands of excess deaths each year. Globally, some 7.7 million people die from respiratory causes, so worldwide the impact of ozone pollution could be very large.”
The findings come a year after the U.S. Environmental Protection Agency (EPA) strengthened its National Ambient Air Quality Standards for ground-level ozone from an annual average of 80 ppb to 75 ppb to reflect growing evidence of the harmful health effects of ozone. A group of leading scientists appointed to advise the EPA had actually recommended stricter health standards for ozone levels – from 60 to 70 ppb.
“Ozone levels outdoors are not always highly correlated to ozone levels indoors, making it difficult to fully evaluate associations between ozone and health outcomes using ambient site monitors,” said study co-author C. Arden Pope III, professor of economics at Brigham Young University. “The reality is that most of us spend the majority of our time indoors. But this study suggests that repeated exposures to elevated ozone levels over time have cumulative effects on respiratory health.”
The new study analyzed data from 448,850 adults ages 30 and older enrolled in 1982 and 1983 in the American Cancer Society Cancer Prevention Study II.
As has been observed in previous studies, the researchers found that fine particulate matter was linked to an increased risk of death from cardiovascular causes when analyzed alone and with ozone. The new finding was that the effects of ozone remained strongly linked to risk of death from respiratory problems, even after fine particle pollution was taken into account.
Other co-authors of the paper are Richard Burnett from Health Canada, the federal health department headquartered in Ottawa; Kaz Ito and George Thurston from the New York University School of Medicine; Daniel Krewski and Dr. Yuanli Shi from the University of Ottawa; and Eugenia Calle and Dr. Michael Thun from the American Cancer Society.
The Health Effects Institute, a non-profit research organization based in Boston, Mass., helped support this research.
Source: University of California, Berkeley, USA