Air pollutants can be dangerous for humans and can come in the form of gases, liquids or other solid particles. Now, new research suggests that air pollution may even contribute to the development of chronic obstructive pulmonary disease (COPD), which blocks airflow and breathing.

Scientists from the Institute of Cancer Epidemiology of the Danish Cancer Society in Denmark analyzed the data of more than 57,000 individuals who were between 50 and 64 years old. The participants completed a questionnaire to further provide the researchers with information on dietary habits, education, smoking, lifestyle and occupational history.

The investigators then linked the subjects to hospital admissions and discharges due to COPD. Pollution exposure at different lengths of time was also estimated and then associated with the participants.

Zorana Andersen, lead researcher of the study, said that overall, there were “significant positive associations between the levels of air pollution proxies and COPD incidence.” She added that after making adjustments for smoking and other factors, “long-term pollution exposure likely is a true risk factor for developing COPD.”

The tendency to develop COPD was also slightly greater among men, obese patients and those who ate less fruit than that of the normal daily intake.

There are about 126,000 deaths caused by COPD each year, among Americans who are at least 25 years old, according to the Centers for Disease Control and Prevention.