Ozone Increases Risk of Death from Respiratory Causes

Long-term exposure to ozone smog increases the risk of death from respiratory causes, according to a study published in today’s New England Journal of Medicine.

The study 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.

The researchers found that people living in areas with the highest concentrations of ozone, such as the Los Angeles metropolitan area and California's Central Valley, had a 25 to 30 percent greater annual risk of dying from respiratory diseases compared with people from regions with the lowest levels of the pollutant. Those locations included the Great Plains area and regions near San Francisco and Seattle.

"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 pulmonary 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.

"Many studies have shown that a high-ozone day leads to an increase in risk of acute health effects the next day, for example, asthma attacks and heart attacks," says George D. Thurston, Sc.D., professor in the Department of Environmental Medicine at NYU School of Medicine, who directed the air pollution exposure assessment part of the study. "What this study says is that to protect the public's health, we can't just reduce the peaks, we must also reduce long-term, cumulative exposure." 

The study is available online at:  www.nejm.org. 

Jerrett M, Burnett RT, Pope CA III, Ito K, Thurston G, Krewski D, Shi Y, Calle E, Thun M. Long-Term Ozone Exposure and Mortality. N Engl J Med 2009; 360: 1085-1095.

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