Health study uses data from war on terrorism Published June 30, 2007 By Gerry J. Gilmore American Forces Press Service WASHINGTON (AFPN) -- When a landmark Defense Department-sponsored health study was launched six years ago, one of its goals was to evaluate the impact of future deployments on long-term health. The investigators did not know how timely the project would be. Today, the Millennium Cohort Study has enrolled tens of thousands of participants who have deployed in support of the war on terrorism, said Navy Cmdr. (Dr.) Margaret Ryan, the study's principal investigator and director of the Defense Department Center for Deployment Health Research, part of the Naval Health Research Center, in San Diego. The study was designed in the late 1990s "in the wake of the first Gulf War to answer some of the most difficult questions that couldn't really be answered retrospectively after that conflict," Commander Ryan said. The joint-service study was established to evaluate the health risks of military deployments, occupational exposures and general military service, Commander Ryan explained, noting that about 108,000 servicemembers have signed up to take part since program enrollment began in July 2001. Participants' health is evaluated over a 21-year period, Commander Ryan said, noting the size of the cohort -- the group participating in the study - likely will total more than 147,000 people. "About 40 percent of our cohort has deployed to one of the more recent operations, either in Iraq or Afghanistan or surrounding regions, in support of the global war on terrorism," she said. Involvement in the study is voluntary and participants are selected randomly, Commander Ryan said. All information is secure and safeguarded, she added. Participants report their health status every three years and can fill out either paper or online surveys, Commander Ryan said. "We do strongly encourage people to use the online option," she said. "It's a very secure way to transmit information." Dr. Tyler C. Smith will replace Commander Ryan as the study's principal investigator later this year, as the Navy physician is slated to take a new duty assignment at Camp Pendleton, Calif. The study is providing valuable data that will help military epidemiologists understand possible cause-and-effect relationships between combat-zone deployments and problems such as post-traumatic stress disorder, Doctor Smith said. "We have the ability to look at a large group of individuals who were deployed and not deployed," he said. "And we can see what factors predict new-onset PTSD, and how PTSD evolves over time. That's what we've been focusing on." Evaluating the incidence of PTSD among servicemembers wasn't possible until recently, "simply because we didn't have a cohort in place like this that's large and population-based," Doctor Smith explained. "So we're learning things that we really haven't been able to investigate in the past," he said.