The Millennium Cohort Study is a long-term research project mandated by Congress and sponsored by the Department of Defense to examine how military service impacts the health and well-being of service members and veterans.
Established in 2001, the Millennium Cohort Study was originally planned to last 21 years, following service members through their military careers until 2022. However, because physical and mental health conditions related to service can appear at any time during or after service, the study was extended through 2068. This allows researchers to track the long-term effects of military service over a lifetime.
Findings from this study help shape policies and programs that directly impact service members and veterans. From improving healthcare and support services to strengthening military readiness, the experiences shared by study participants play a key role in making a difference. Their contributions help create better prevention and treatment programs, ensuring that those who serve receive the care and resources they need.
With more than a quarter of a million service members enrolled since 2001, the Millennium Cohort Study is the largest and longest-running DoD research effort focused on the strength, health, and readiness of the U.S. Armed Forces. By sharing their experiences, participants contribute to research that improves support for service members and veterans both now and in the future.
Millennium Cohort Study participants reflect the composition of the U.S. Armed Forces and represent service members across all branches and ranks.
- The majority of participants (69%) are male, while women make up 31%.
- The largest proportion of participants served in the Army (43%), followed by the Air Force (31%), Navy (15%), Marine Corps (9%), and Coast Guard (2%).
- Over 60% of participants deployed at least once during their military service.
- At the time of study enrollment, 58% of participants were junior enlisted personnel, 26% were senior enlisted, and 17% were officers.
- Over 60% of participants have separated from military service.
- 73% of the cohort are married
- 49% have at least an associate's degree
- 93% have either never smoked or have quit smoking
- 34% of men and 22% of women report experiencing tinnitus
- Participants get an average of 6.4 hours of sleep per night
Principal Investigator
Rudy Rull, PhD, MPH is the Principal Investigator of the Millennium Cohort Study at the Naval Health Research Center. Dr. Rull received his PhD and MPH in Epidemiology from the University of California, Los Angeles and BA in Environmental Sciences from the University of California, Berkeley. In addition to military health, his research has focused on the assessment of environmental exposures to metals, pesticides, and other pollutants using biological markers, environmental databases, geographic information systems and mapping technologies, and the effects of these exposures on cancer, respiratory health, and birth defects.
Past Principal Investigators
| Gregory C. Gray, MD, MPH, Captain, USN, Retired | 1999 - 2001 |
| Margret A. K. Ryan, MD, MPH, Captain, USN, Retired | 2001 - 2008 |
| Tyler C. Smith, PhD, MS | 2008 - 2011 |
| Nancy F. Crum, MD, MPH | 2011 - 2013 |
| Martin R. White, MPH | 2013 - 2014 |
| David D. Luxton, PhD | 2014 - 2015 |
| CAPT Dennis Faix, MD, MPH, MC, USN | 2015 - 2017 |
The Study Staff
Our study staff of epidemiologists, biostatisticians, research psychologists, analysts, programmers and research coordinators are comprised of both military and civilian professionals. The staff is located at the Deployment Health Research Department, Naval Health Research Center in San Diego, California.