Since 2001, the Department of Defense has been conducting a large-scale, long-term study of military personnel and veterans to help close the information gap. The Millennium Cohort Study randomly selected the first of what were eventually about 150,000 participants from all service branches, the National Guard and the reserves, asking them to answer health-related questionnaires once every three years over a span of 21 years.

The Department of Defense's Millennium Cohort Study is excited to announce the launch of its next follow-up survey for over a quarter of a million service members and veterans who previously enrolled in this landmark study. This longstanding research program, managed by the Naval Health Research Center (NHRC) in San Diego, is the largest and longest-running health study in military history and is designed to understand the long-term health effects of military service.

The Millennium Cohort Study is currently enrolling invited personnel and expects to add 50,000 service members to reach a goal of over 200,000 participants by early 2012.

Service members who were currently deployed or had returned from a deployment had significantly shorter adjusted sleep duration and increased adjusted odds of reporting trouble sleeping compared to those who had not deployed.

Service members with one or more mental health disorders prior to deployment were two- and-a-half times more likely to screen positive for PTSD post-deployment compared to those with no mental health disorders, after controlling for pre-deployment PTSD, physical injury severity and a host of other risk factors.

Participants who engaged in less physical activity were more likely to screen positive for PTSD. Those who reported at least 20 minutes of vigorous activity twice a week had significantly reduced odds for new-onset and persistent PTSD symptoms.

Deployment as a Navy individual augmentee (IA) was not significantly associated with newly reported PTSD or symptoms of mental health problems (including PTSD, depression, panic or other anxiety and alcohol-related problems) compared with non-IA deployment.

Analysis of U.S. service members who had deployed either once or multiple times revealed that both groups shared very similar PTSD trajectories over time, with the vast majority (83% single deployers, 85% multiple deployers) displaying a low-stable (resilient) symptom pattern that lasted from pre-deployment to several years post-deployment. The other PTSD symptom trajectory patterns included moderate-improving (8%, 8.5%), worsening-chronic (6.7%, 4.5%), high-stable (2.2% single deployers only) and high-improving (2.2% multiple deployers only).

Military healthcare professionals have similar rates of new-onset PTSD or depression compared to those in other military occupations. Similar to other types of military personnel, combat exposure was the key factor that increased the rates of new-onset PTSD/depression in this sample, as deployed healthcare professionals with combat exposure had twice the odds of new-onset PTSD/depression compared to those deployed without combat exposure.