May 21, 2008

To evaluate the impact of military service on long-term health, the Millennium Cohort Study, the first of its kind, is tracking a large population of Service members over time. The DoD-funded study involves a representative sample of the U.S. military - both active-duty and Reserve/Guard forces. Launched in 2001, the study will run through 2022.

All of the military services and the Department of Veterans Affairs collaborated in the design of the study. The questionnaire includes self-reported symptoms, medical outcomes, physical and psychological health, complementary and alternative medicine use, occupational exposures, and health behaviors such as smoking and drinking. Standardized instruments, such as the Patient Health Questionnaire, the Medical Outcomes Study Short Form-36 for Veterans, and the Posttraumatic Stress Disorder Checklist-Civilian Version, are included.

Randomly selected from the military population, study participants have been enrolled in three successive panels, one each in 2001, 2004 and 2007, that sum to approximately 150,000. Each panel is surveyed every three years following its baseline through 2022. The second follow-up has been completed for the 2001 panel, along with the first follow-up for the 2004 panel and the baseline for the 2007 panel.

"We have never been able to do this before," says Tyler C. Smith, PhD, Director of the DoD Center for Deployment located at the Naval Health Research Center in San Diego and the principal investigator. "In the past, U.S. military studies have focused on smaller cohorts, or have been cross-sectional or retrospective in design."

Sixty percent of the 77,047 Panel 1 participants have been deployed in previous military operations and forty percent in the Global War on Terror (GWOT), whereas sixty percent of the 31,110 Panel 2 participants have had GWOT deployment. "The study will allow us to temporally assess the long-term health impact of deployment and other military occupational exposures," Smith explains. "We'll be able to see symptom resolution and the onset of new symptoms in a prospective way."

Some findings on post-traumatic stress disorder (PTSD) have already been published. Service members who had experienced prior violent or sexual assault in their lives were more vulnerable to PTSD after deployment. It was also found that exposure to actual combat rather than deployment itself was a factor in the onset of PTSD symptoms. Additional findings will be released in the coming months.

Unlike retrospective study designs employed after the 1991 Gulf War, the Millennium Cohort Study will enable prospective evaluation of the health outcomes of military service. "We will now be able to be proactive and get answers to questions that we couldn't get after the 1991 Gulf War," says Smith.