U.S. military personnel deployed to Iraq and Afghanistan face an increased risk for developing respiratory symptoms, including persistent or recurring cough and shortness of breath, a large-scale military study has shown.

Combat stress along with air pollution could be to blame, researchers say.

The findings stem from the Millennium Cohort Study, an ongoing study designed to investigate long-term health consequences related to military service.

Among nearly 39,000 military personnel free of persistent or recurring cough or shortness of breath at the outset, 14 percent of deployers to the wars in Afghanistan and Iraq suffered new respiratory symptoms compared with 10 percent of non-deployers not assigned to those war zones, the researchers found.

Still, they wrote in the American Journal of Epidemiology, The current results are reassuring in that no increase in reported asthma, chronic bronchitis, and emphysema was noted in the short term.

According to Dr. Besa Smith from the Department of Defense Center for Deployment Health Research at the Naval Health Research Center in San Diego and colleagues, land-deployed soldiers and Marines were hardest hit by respiratory woes.

Deployed Army troops experienced a 73 percent increased likelihood of new respiratory symptoms, while deployed Marines had a 49 percent increased likelihood, whereas no significant associations between deployment and respiratory symptoms were observed among Air Force or Navy/Coast Guard personnel.

This suggests to the researchers that exposure related to ground combat, including stress, may be important in the development of service-related respiratory symptoms.

A recent environmental sampling study revealed geologic dusts, smoke from burn pits and heavy metal condensates, including arsenic and lead, as major types of air pollutants in 15 locations of deployment in the Middle East, including Iraq.

Respiratory illnesses, the investigators note, were reported to be associated with military deployment in the 1991 Gulf War and are again being reported by deployers to the wars in Iraq and Afghanistan.

In the current analysis, military personnel on average were followed for 2.6 years. Hence, the researchers said they only have identified acute conditions and missed chronic conditions that develop over longer time periods.

In future analyses of the Millennium Cohort Study participants, investigators will be able to determine whether respiratory symptoms resolve or progress over time.

SOURCE: American Journal of Epidemiology, December 2009.