TUESDAY, Nov. 25 (HealthDay News) -- Long-term exposure to diesel exhaust fumes may increase the risk of chronic obstructive pulmonary disease (COPD), which includes lung conditions such as bronchitis and emphysema.

U.S. researchers studied the job and health records of more than 30,000 railway workers and found that those who worked on diesel trains (engineers, brakemen, conductors) were more likely to die of COPD than those who worked in ticketing, signaling, maintenance, or administration.

The health records used were from the U.S. Railroad Retirement Board, dating back to 1959.

Diesel exhaust includes fine particulate matter and combustion gases that can be inhaled deep into the lungs. Previous studies have made a link between the organic compounds in diesel exhaust and allergy, airway inflammation, and changes in airway functioning.

The COPD risk for workers directly exposed to diesel exhaust increased by 2.5 percent per year of employment. That risk fell slightly after adjusting for smoking, a known risk factor for COPD, said lead researcher Dr. Jaime Hart, of Brigham and Women's Hospital and Harvard Medical School in Boston, according to a news release from the two institutions.

The study was published in the journal Occupational and Environmental Medicine.

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