March 16, 2009 -- On days when ozone levels are high, breathing can be difficult and exercising outdoors is usually discouraged. Now research shows that breathing in the gas year in and year out can lead to chronic and deadly lung disease.
A study of nearly half a million people found that the risk of dying from lung disease went up by as much as 50 percent in cities with the highest levels of ozone. Repeated daily exposures to even moderate levels of ozone proved far worse than occasional exposure to high levels.
It is the first study to look at the effects on the lungs of breathing in ozone, day after day, year after year. And it suggests that current regulations may be missing the mark.
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"The standard we have in the United States protects you against peaks," said George Thurston, an environmental health scientist at New York University. "It doesn't do anything to protect you against cumulative long-term exposure."
Exposure is widespread. Ozone, or O3, comes from vehicle emissions and coal-fired power plants, among other sources. Wind spreads the gas, which tends to sit and smother cities in valleys, like Los Angeles.
Way up high in the atmosphere, ozone absorbs ultraviolet rays and protects the planet. Down here, however, the gas irritates and inflames our lungs, which is one reason why exercising in polluted places can exacerbate asthma and other health problems.
Over time, chronic exposure to ozone can eat away at the lungs and cause serious diseases. But evidence has been murky, because most studies have looked at all types of pollution together, and few have separated the harm done to the lungs from harm done to the heart.
So, to quantify for the first time what repeated ozone exposure actually does to lung health, Thurston and colleagues tapped into a database of nearly 500,000 people, collected by the American Cancer Society.
The data set included information about age, race, sex, weight, alcohol use, and nearly everything else that might influence health. The researchers also collected 20 years-worth of pollution records from the cities where study participants lived.
After factoring in all the variables, analyses showed that people who lived in the smog-filled Los Angeles basin were 50 percent more likely to die from lung disease than people with no ozone exposure at all.
In New York City, the chances of dying from lung disease went up about 25 percent. In Seattle, one of the most ventilated cities in the country, ozone upped the risk by about 13 percent. Results appeared this week in the New England Journal of Medicine.
Fewer than 10 percent of the population dies from lung disease each year. But the effects of ozone are significant enough to cause concern, said Douglas Dockery, an environmental epidemiologist at the Harvard School of Public Health in Boston.
"This has very significant implications in terms of policy-setting," Dockery said. "The standard is really based on what the maximum is for a given day, but this suggests that there might be a need for average annual limits."
Staying inside is helpful for particularly high-ozone days, Thurston added. But it's not a realistic long-term strategy.
"You can run, but you really can't hide," he said. "You have to breathe the air, and you have to go outside. The air should be cleaner. That's the message."
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