July 27 (HealthDay News) -- Ozone levels considered safe under current standards can have a negative effect on lung function in healthy people, say U.S. researchers.

The National Ambient Air Quality Standard allows for ozone concentrations of up to 75 parts per billion over an eight-hour period. But a new study "found that 6.6 hours exposure to mean ozone concentrations as low as 70 parts per billion have a significant negative effect on lung function," Edward Schelegle, of the University of California, Davis, said in a news release from the American Thoracic Society.

He and his colleagues studied lung function in 31 healthy nonsmokers who were exposed to ozone concentrations of 60, 70, 80 and 87 parts per billion, or filtered air, while doing moderate exercise. They found that significant decreases in lung function and respiratory symptoms occurred at ozone concentrations of 70 parts per billion or more, beginning after 5.6 hours of exposure.

"These data tell us that even at levels currently below the air quality standard, healthy people may experience decreased lung function after just a few hours of moderate to light exercise, such as bicycling or walking," Schelegle said.

"While these changes were fully reversible within several hours, these findings highlight the need to study susceptible individuals, such as asthmatics, at similar ozone concentrations and durations of exposure," he said. "These studies are needed to better understand the acute rise in hospitalizations that often occur in conjunction with high-ozone periods."

In addition, the researchers urged more study to better understand the mechanisms that determine individual ozone responsiveness in both healthy and susceptible people.

"Understanding how these mechanisms change with repeated daily exposure is critical, especially as ambient ozone levels are often elevated several days in a row," Schelegle said.

The study appears in the August 1 issue of the American Journal of Respiratory and Critical Care Medicine.

SOURCE: American Thoracic Society, news release, July 26, 2009