Traffic pollution tied to increased emphysema risk

NEW YORK (Reuters Health) - People who spend years living near high-traffic roadways may be more likely to develop emphysema and related lung problems than those who live in less-traveled areas, a new study suggests.

Research has shown that air pollution can exacerbate symptoms in people with lung diseases like asthma and chronic obstructive pulmonary disease (COPD), a group of serious lung conditions that includes emphysema and chronic bronchitis.

But whether long-term exposure to pollution affects the odds of developing COPD in the first place has been unclear.

In the new study, researchers found that among nearly 53,000 Danish adults followed for up to 35 years, those estimated to have the greatest cumulative exposure to traffic pollution were more likely to develop COPD than those with the least exposure.

The findings, reported in the American Journal of Respiratory and Critical Care Medicine, point to an association between traffic pollution and COPD risk. They do not, however, prove cause-and-effect.

Cigarette smoking is the primary cause of COPD, estimated to be behind more than 95 percent of cases. Other environmental factors, such as heavy exposure to dust from coal, grain or wood, may also lead to COPD.

The current findings raise the possibility that long-term exposure to traffic pollution contributes to the risk in some people -- particularly those made vulnerable by certain health conditions, like asthma.

If that’s the case, the risk of any one person developing COPD due to such exposure would be “very small,” as compared with smoking or exposure to second-hand smoke, according to lead researcher Zorana J. Andersen, of the Danish Cancer Society in Copenhagen.

Still, she told Reuters Health in an email, on the population level, even a small risk associated with traffic pollution would “not be negligible,” considering the millions of people living in high-traffic urban areas.

The findings are based on 52,799 adults ages 50 to 64 who completed questionnaires on their health and lifestyle factors, including smoking history, in the mid-1990s.

Andersen’s team used data from the Danish national hospital register to find any first-time admissions for COPD in the group between 1971 and 2006. They also estimated individuals’ long-term exposure to traffic pollutants based on their residential addresses throughout the study period.

Overall, just over 3 percent of participants had a first-time hospital admission for COPD during the study period.

When the researchers looked at participants’ average long-term exposure to nitrogen dioxide -- a pollutant produced by car exhaust -- they found that those in the top 25 percent for exposure were more likely to be hospitalized for COPD than those in the bottom 25 percent.

The association between traffic pollution and COPD risk was stronger among people with asthma or diabetes than those without the conditions.

This, according to Andersen’s team, raises the possibility that people with health conditions that cause systemic inflammation in the body might be more vulnerable to any effects of traffic pollution on lung function.

However, the researchers also caution that, in statistical terms, these associations were weak or of “borderline” significance.

This, they write, calls for “caution in interpreting the strength of (the) reported associations and replication of these results by other studies.”

Other limitations of the study include the fact that participants’ pollution exposure was estimated based on their addresses; individuals’ actual pollution exposure, from a range of sources, was not known.

Even so, Andersen said that people should be aware that heavy exposure to traffic pollution has been associated with a number of health risks -- including asthma development and deaths from heart disease and stroke. The American Heart Association suggests that people with heart disease and other at-risk individuals -- including the elderly and those with risk factors for heart disease, like diabetes and high blood pressure -- try to limit their exposure to congested roadways.

On a broader level, Andersen noted, links between air pollution and health risks are important in supporting policies aimed at pollution control.

SOURCE: American Journal of Respiratory and Critical Care Medicine, online September 24, 2010.