Researchers in Denmark say that long-term exposure to low-level air pollution may increase the risk of severe chronic obstructive pulmonary disease (COPD).
"We found significant positive associations between levels of all air pollution proxies and COPD incidence," said Dr. Zorana Andersen, lead researcher on the study.
Dr. Andersen, and colleagues used data from the Danish Diet, Cancer, and Health Study, which consisted of more than 57,000 individuals between the ages of 50 and 64 who lived in Copenhagen or Aarhus, the first and second largest cities in Denmark, between 1993 and 1997.
"When we adjusted for smoking status and other confounding factors, the association remained significant, indicating that long-term pollution exposure likely is a true risk factor for developing COPD," Dr. Andersen said.
These associations were slightly stronger for men, obese patients and those eating less than 240 grams of fruit each day.
But notably, the effect of air pollution on COPD was strongest in people with pre-existing diabetes and asthma.
"These results are in agreement with those of other cross-sectional studies on COPD and air pollution, and longitudinal studies of air pollution and lung function, and strengthen the conclusion that air pollution is a causal agent in development of COPD," said Dr. Andersen.
The research was published in the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.