BETHESDA, MD—Many reports have suggested that servicemembers who deployed to Iraq and Afghanistan developed respiratory illnesses at higher-than-expected rates, but study results looking at increased rates of asthma have been mixed. A new study by Navy and VA researchers might resolve the issue.

The researchers discovered that deployment to the region by itself made no difference in new-onset asthma rates. Seeing combat, however, increased the risk of developing asthma by 24% in women and 30% in men, the researchers reported in the American Journal of Epidemiology.1

The increased risk associated with combat was eclipsed by several other factors, including being overweight or obese, serving in certain specialties, experiencing life stressor events and suffering from post-traumatic stress disorder.

Development of asthma in servicemembers remains a serious concern for the military, as the condition often requires medications and treatments difficult to obtain in a combat environment and can interfere with adherence to safety precautions, such as wearing a protective mask. In addition, severe cases can lead to absences from work and even require evacuation and redeployment, with direct impact on unit readiness.

Respiratory illnesses, including asthma, have been the second-most commonly self-reported noncombat-related diagnoses among troops that deployed in Operation Enduring Freedom and Operation Iraqi Freedom. High rates also have been a concern among Gulf War veterans and those who deployed during Operation New Dawn.

The researchers used data from the Millennium Cohort Study, a longitudinal study which tracks participants from all branches of the U.S. military who are active duty or serve with the National Guard or Reserve units. Launched in 2001, the study surveys participants on lifestyle characteristics, military experiences, health outcomes and behaviors every three years.

A total of 94,241 participants responded to a baseline survey and one or more follow-up surveys. The survey data was supplemented by demographic and service-related information from the Defense Manpower Data Center. After eliminating participants who had asthma at baseline or had undetermined initial asthma or deployment status or missing covariate data, the final number of participants was 75,770.

New-onset asthma was identified in 1,452 men (2.7%) and 1,055 women (4.6%) who responded negatively at baseline to a question about having previously been told by a healthcare professional that they had asthma and positively in a subsequent survey that asked about a diagnosis in the past three years.

A U.S. Special Forces Soldier, attached to Special Operations Task Force-Afghanistan, waits for nightfall prior to starting a nighttime operation in 2016. A new study suggested that combat, not just deployment, affected risk of developing asthma. Army photo by Sgt. Connor Mendez

Combat Experience

To determine combat experience, the researchers asked participants whether they were personally exposed to “witnessing death, witnessing physical abuse, dead and/or decomposing bodies, maimed soldiers or civilians, or prisoners of war or refugees.” Answers were cross-indexed to data from the Contingency Tracking System that showed deployment dates to Iraq, Afghanistan and noncombat zones.

“Based on the combat experience question on the survey, it would be difficult to distinguish between being a witness versus being an active combatant,” said study lead author Anna C. Rivera, MD, of the Henry M. Jackson Foundation for the Advancement of Military Medicine in Bethesda, MD, and the Naval Health Research Center in San Diego. “However, the cumulative stresses associated with deployment, including specific aspects of combat experiences, may contribute to the physical and mental toll of chronic stress that could increase the risk of new-onset asthma.”

The study’s finding of increased risk of asthma associated with experiencing or witnessing violence aligns with other reports that demonstrated that childhood exposure to traumatic stress (child abuse, domestic violence, parental mental illness or incarceration) significantly increased the risk of subsequent asthma onset.2

A Harvard study determined that women who experienced domestic violence had a 37% increase in risk of new-onset asthma, and those who witnessed but not themselves experienced domestic abuse had a 21% increase in risk. The authors noted that exposure to violence and other major psychosocial stressors affect the immune system and inflammation, which have a role in asthma development.3

The stress associated with medical work in a war zone might contributed to the increased risk of new-onset asthma seen among study participants with healthcare specialties. “Because of the specific questions on the survey used to assess combat experience (such as personally being exposed to death, maimed or injured personnel, or prisoners of war), it is possible that deployed health care personnel would screen positive for combat experience, particularly those working in trauma care,” Rivera told U.S. Medicine.

In addition to combat experience, the Navy study found that male Hispanic service members had a 28% increased risk of asthma, and female Hispanics had a 37% increased risk.

In addition, “we did detect an increased risk for developing new-onset asthma associated with having a body mass index in the overweight or obese range, which is consistent with other asthma epidemiologic studies,” Rivera said.

Notably, the study did not find that smoking increased the risk of new-onset asthma. “The current body of scientific evidence is not clear on whether smoking increases the risk of asthma,” explained co-author Rudolph P. Rull, MD, of the Deployment Health Research Department at the Naval Health Research Center in San Diego. “However, smoking does make symptoms worse in individuals who already have asthma.”

1. Rivera AC, Powell TM, Boyko EJ, Lee RU, Faix DJ, Luxton DD, Rull RP; Millennium Cohort Study Team. New-Onset Asthma and Combat Deployment: Findings From the Millennium Cohort Study. Am J Epidemiol. 2018 Oct 1;187(10):2136-2144.

2. Exley D, Norman A, Hyland M. Adverse childhood experience and asthma onset: a systemic review. European Respiratory Review 2015 24: 299-305.

3. Subramanian SV, Ackerson LK, Subramanyam MA, Wright RJ. Domestic violence is associated with adult and childhood asthma prevalence in India. Int J Epidemiol. 2007 Jun;36(3):569-79. Epub 2007 Feb 28.