Emphysema is considered a smoker's disease. But it turns out, exposure to air pollution may lead to the same changes in the lung that give rise to emphysema.
A new study published Tuesday in JAMA finds that long-term exposure to slightly elevated levels of air pollution can be linked to accelerated development of lung damage, even among people who have never smoked.
The study looked at the health effects of breathing in various pollutants, including ground-level ozone, the main component of smog.
The researchers found that people in the study who were exposed for years to higher-than-average concentrations of ground-level ozone developed changes to their lungs similar to those seen in smokers.
"We found that an increase of about three parts per billion [of ground-level ozone] outside your home was equivalent to smoking a pack of cigarettes a day for 29 years," says one study author, Joel Kaufman, a physician and epidemiologist at the University of Washington.
The study involved nearly 7,000 adults living in six U.S. cities: Chicago, Los Angeles, Baltimore, St. Paul, Minn., New York City and Winston-Salem, N.C. Generally, people in the study were exposed to annual average concentrations of between 10 and 25 parts per billion of ground-level ozone outside their homes.
But there's no reason to believe that the pockets of elevated ozone exposure are limited to those cities. Kaufman says people in communities all over the U.S. can be exposed to similar concentrations — which can vary from day to day, season to season and year to year. Typically, ground level ozone — or smog — forms when pollution that's released from cars' tailpipes and from smokestacks bakes in the sunlight. (The EPA has this simple explainer.) Ozone is typically highest on hot, sunny days.
"It was a very large surprise to us to see that the effects were in the same magnitude as cigarette smoking, which is the best-established and most-recognized cause of emphysema," Kaufman says.
In order to evaluate the changes to the participants' lungs, each person had up to five CT scans over more than a decade. These scans give a 3D picture of the lungs and can detect changes that precede the development of symptoms. During the same time period, the researchers measured levels of pollution, including ozone, in the participants' communities.
"When airways get narrowed and damaged, it's harder to move air out of the lungs and air gets trapped," explains Emily Brigham, a pulmonologist and assistant professor of medicine at Johns Hopkins University. She was not involved in this study, but she also researches how environmental exposures can influence lung health.
At the very early stages of respiratory disease, people may not notice much. But over time, these changes lead to emphysema symptoms, including breathlessness. "It does tend to get worse over time if you continue the exposures," says Brigham. And the changes are generally believed to be irreversible.
Chronic respiratory disease (which includes chronic obstructive pulmonary disease and emphysema) is a leading cause of death in the U.S.. The World Health Organization estimates that each year 7 million premature deaths around the world are linked to air pollution.
These new findings help to answer a very important question about COPD, Brigham says.
"We know ... that a significant proportion of the U.S. population who has COPD actually, are never smokers," Brigham says. So, what's causing their lung disease? "I think this [study] gives us a partial answer."
Overall, most types of air pollution have been declining in the U.S. — in part, thanks to the policies put in place by the Clean Air Act.
But ground level ozone — or smog — has been harder to control. One explanation is that with increasing numbers of hot days, the conditions are more favorable to the formation of ozone.
"And so as climate change progresses, we expect that vulnerable populations and — even healthy populations — are going to see increased effects," Brigham says.
In the past, the larger concern about ozone was the short-term exacerbation of symptoms during smog-alert days for people living with chronic lung disease such as asthma or COPD. The effects of long-term, chronic exposures were not well understood.
"In the past, the EPA has not accepted that COPD is caused by long-term, chronic air pollution," says George Thurston, a professor of environmental medicine at NYU Langone Health.
But, now, this study adds to the evidence that the benefits of cleaning the air are even larger than previously calculated because the findings suggest that long-term exposure to air pollution is damaging to lung health.
Thurston says if these long-term cumulative effects were to be included in policymakers' cost-benefit calculations, "the benefits will even more so outweigh the the cost of moving forward on cleaning the air."
MARY LOUISE KELLY, HOST:
To new evidence now that long-term exposure to air pollution, especially ground-level ozone, can speed up the development of emphysema, even in nonsmokers. NPR's Allison Aubrey reports ground-level ozone is the primary ingredient in smog and is linked to climate change.
ALLISON AUBREY, BYLINE: It's long been known that for people who have lung disease due to cigarette smoking or asthma, air pollution can make it worse. But this new study suggests that many more of us are vulnerable. Study author Joel Kaufman of the University of Washington says he and his collaborators found that living in a community with slightly elevated concentrations of ground-level ozone can speed up the progression of lung damage.
JOEL KAUFMAN: We found that an increase of about three parts per billion outside your home was equivalent to smoking a pack of cigarettes a day for 29 years.
AUBREY: The study included about 7,000 adults living in a bunch of different cities, including Los Angeles, Baltimore, St. Paul and Winston-Salem. But Kaufman says people in communities all over the U.S. can be exposed to similar concentrations of ground-level ozone. So these results are bad news.
KAUFMAN: That was a very large surprise to us to see that the effects were in the same magnitude as cigarette smoking, which is the best-established and most well-recognized cause of emphysema.
AUBREY: To track changes in the lungs, all of the participants in the study had up to five CT scans over a decade, which give a 3D picture of the lungs.
Emily Brigham is a pulmonologist at Johns Hopkins University. She was not involved in this study, but she explains what you can see at the early stages of respiratory disease.
EMILY BRIGHAM: What we're able to see is this loss of normal structure. And when that happens and the airways get damaged and narrowed, it's harder for air to move in and out of the lung, and air gets trapped.
AUBREY: She says at the early stages, people may not notice much. But over time, emphysema symptoms develop.
BRIGHAM: What patients typically start to feel when their damage reaches a certain point is breathlessness, and it does tend to get worse over time if you continue the exposures.
AUBREY: And the changes are generally believed to be irreversible. Brigham says these findings help to answer a very important question - what explains so many cases of COPD, which is an umbrella term for several respiratory diseases, including emphysema.
BRIGHAM: A significant proportion of the U.S. population who has COPD actually are never smokers. So what is causing their underlying lung disease? And I think this gives us a partial answer.
AUBREY: Now, overall, levels of air pollution in the U.S. have been declining, but ground-level ozone, or smog, has been harder to control. That's because it's formed when pollution released from sources such as cars and smokestacks bake in the sunlight. And on very hot days, the conditions are favorable to produce more smog.
BRIGHAM: And so as climate change progresses, we expect that these vulnerable populations and even healthy populations are going to see increased effects.
AUBREY: Which may mean more people at risk of developing respiratory disease.
Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.