Millennium Cohort Study (United States)

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The Millennium Cohort Study is an ongoing longitudinal cohort study headquartered at the Naval Health Research Center in San Diego, California and designed to evaluate any long-term health effects of military service, including deployments.[1] It is the largest population-based prospective health project in US military history,[2][3][4] currently collecting data on over 200,000 enrolled participants. Investigators that conduct the Millennium Cohort Study include uniformed and non-uniformed scientists from the Army,[5] Navy,[6] Air Force,[7] Department of Veterans Affairs[8] and academic institutions.[9][10]



After the 1991 Gulf War, the United States Department of Defense recognized the need to collect prospective exposure and health information that may be associated with the long-term health of service members .[11][12] The Millennium Cohort Study was designed to address that need. Pilot studies were conducted in 2000; by mid-2001, the Millennium Cohort Study's first enrollment period was launched, collecting baseline data from over 77,000 people.


The most methodologically rigorous epidemiological study on American military personnel deployed to Iraq and Afghanistan[13] is funded by the US Department of Defense,[14] and supported by military, United States Department of Veterans Affairs, and civilian researchers. Over 200,000 military personnel are members of the cohort. The Millennium Cohort Study began with a random sample of US Military members including active duty, Reserve, and National Guard members from all services. Surveys are sent to this representative sample of US military personnel every three years until 2022, through email and the United States Postal Service, requesting that they submit their data online or via the mail service. Approximately 42% of Millennium Cohort participants have left military service and the study will continue to follow all participants through their Active duty, Reserve, National Guard careers and civilian endeavors.


Prospective data analyses are underway to assess health outcomes including Suicide,[15] Posttraumatic stress disorder,[16][17] depression,[18] hypertension, respiratory symptoms and illness,[19] immune responses, chronic multi-symptom illness, CHD and CVD, and modifiable health behaviors such as smoking, alcohol use,[20] sleep,[21] and physical activity that may be associated with deployment in support of the current wars.[22] Currently, more than 60% of Millennium Cohort participants have deployed in support of the wars in Iraq and Afghanistan.


In 2011 the Millennium Cohort Study was expanded to include 10,000 spouses of Millennium Cohort members. The substudy, The Millennium Cohort Family Study's[23] goal is to gain a more complete understanding of the military experience and its resultant impact on the health and well-being of service members and their families.

In 2020 invitations were sent to an additional 500,000 service members,[24] including active duty, Reserve, and National Guard personnel. Invited participants will receive an email to their Department of Defense (DoD)-registered email address. The new members will be asked to complete a confidential online survey asking for input on their individual experiences in the military. They will also be asked to participate in follow-up surveys through their military service and beyond.


  1. ^ Ryan, Margaret A.K.; Smith, Tyler C.; Smith, Besa; Amoroso, Paul; Boyko, Edward J.; Gray, Gregory C.; Gackstetter, Gary D.; Riddle, James R.; Wells, Timothy S.; Gumbs, Gia; Corbeil, Thomas E.; Hooper, Tomoko I. (February 2007). "Millennium Cohort: enrollment begins a 21-year contribution to understanding the impact of military service". Journal of Clinical Epidemiology. 60 (2): 181–191. doi:10.1016/j.jclinepi.2006.05.009. PMID 17208125.
  2. ^ Naval Health Research Center (2011-07-14). "NHRC Launches Next Survey Cycle of Largest DoD Population-Based Military Health Study". Retrieved 2013-08-15.
  3. ^ Naval Health Research Center (2011-07-19). "The Largest DoD Population-Based Military Health Study Launched Next Survey Cycle, Hopes to Enroll Military Members and Spouses" (PDF). Naval Health Research Center. Retrieved 2013-08-15.
  4. ^ Michel E. Kilpatrick (April 2010). "What We Can Learn in 21 Years". [Archived by WebCite® at Archived] from the original on 2011-08-03. Retrieved 2013-08-15. {{cite web}}: Check |archiveurl= value (help)
  5. ^ Military Operational Medicine Research Program(MOMRP) (2003-03-26). "Gulf War Illnesses Research Program (GWIRP)". Retrieved 2013-08-15.
  6. ^ Naval Health Research Center (1999-09-30). "Military Population Health - Millennium Cohort study". Retrieved 2013-08-15.
  7. ^ Navy Lt. Jennifer Cragg (2008-05-16). "Military medical advancements benefit civilian health care". American Forces Press Service. Retrieved 2013-08-15.
  8. ^ U.S. Department of Veterans Affairs (2010-04-01). "VA, DoD Teaming Up to Track Health of Military Forces". Archived from the original on 2012-08-05. Retrieved 2013-08-15.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  9. ^ Karen Bowman & Cynthia Monticue (2010-04-05). "First Conference on Military Families Held". Retrieved 2013-08-15.
  10. ^ National Cancer Institute (2010-07-08). "Cohort Consortium Members - EGRP". Retrieved 2013-08-15.
  11. ^ Lyla M. Hernandez, Jane S. Durch, Dan G. Blazer II, and Isabel V. Hoverman, Editors; Committee on Measuring the Health of Gulf War Veterans, Institute of Medicine (1999). Gulf War Veterans: Measuring Health. doi:10.17226/9636. ISBN 978-0-309-06580-1. PMID 25077231. Retrieved 2013-08-15. {{cite book}}: |author= has generic name (help)CS1 maint: multiple names: authors list (link)
  12. ^ Office of the Special Assistant for Gulf War Illnesses, Medical Readiness, and Military Deployments (1998-11-11). "Lessons Learned And Recent Initiatives". Retrieved 2013-08-15.{{cite web}}: CS1 maint: multiple names: authors list (link)
  13. ^ McNally, R. J. (17 May 2012). "Are We Winning the War Against Posttraumatic Stress Disorder?". Science. 336 (6083): 872–874. Bibcode:2012Sci...336..872M. doi:10.1126/science.1222069. PMID 22605766. S2CID 27247433.
  14. ^ Force Health Protection & Readiness (June 2001). "Millennium Cohort Study to Watch Military Health". American Forces Press Service. Retrieved 2013-08-15.
  15. ^ LeardMann, Cynthia A.; Powell, Teresa M.; Smith, Tyler C.; Bell, Michael R.; Smith, Besa; Boyko, Edward J.; Hooper, Tomoko I.; Gackstetter, Gary D.; Ghamsary, Mark; Hoge, Charles W. (7 August 2013). "Risk Factors Associated With Suicide in Current and Former US Military Personnel". JAMA. 310 (5): 496–506. doi:10.1001/jama.2013.65164. PMID 23925620.
  16. ^ Cynthia A LeardMann, Tyler C Smith, Besa Smith, Timothy S Wells and Margaret A K Ryan for the Millennium Cohort Study Team (2008-12-19). "Baseline self reported functional health and vulnerability to post-traumatic stress disorder after combat deployment: prospective US military cohort study". BMJ. 338: b1273. doi:10.1136/bmj.b1273. PMC 2671472. PMID 19372117.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ U.S. Department of Veterans Affairs (2007-11-25). "New onset and persistent symptoms of post-traumatic stress disorder self reported after deployment and combat exposures: prospective population based US military cohort study". BMJ. 336 (7640): 366–71. doi:10.1136/bmj.39430.638241.AE. PMC 2244768. PMID 18198395.
  18. ^ Tyler C. Smith, Deborah L. Wingard, Margaret A.K. Ryan, Donna Kritz-Silverstein, Donald J. Slymen, and James F. Sallis, for the Millennium Cohort Study Team (January 2009). "PTSD Prevalence, Associated Exposures, and Functional Health Outcomes in a Large, Population-Based Military Cohort". Public Health Rep. Association of Schools of Public Health. 124 (1): 90–102. doi:10.1177/003335490912400112. PMC 2602934. PMID 19413031.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  19. ^ David Loebsack (2010-02-10). "Respiratory Conditions Investigated Among the Deployed". Military Health System. Retrieved 2013-08-15.
  20. ^ Jacobson, Isabel G. (13 August 2008). "Alcohol Use and Alcohol-Related Problems Before and After Military Combat Deployment". JAMA. 300 (6): 663–75. doi:10.1001/jama.300.6.663. PMC 2680184. PMID 18698065.
  21. ^ Amber D. Seelig, Isabel G. Jacobson, Besa Smith, Tomoko I. Hooper, Edward J. Boyko, Gary D. Gackstetter, Philip Gehrman, Carol A. Macera, Tyler C. Smith for the Millennium Cohort Study Team (2010-12-01). "Sleep Patterns Before, During, and After Deployment to Iraq and Afghanistan". Sleep. 2010 Associated Professional Sleep Societies, LLC. 33 (12): 1615–1622. doi:10.1093/sleep/33.12.1615. PMC 2982731. PMID 21120123.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  22. ^ Molly L Kelton, Cynthia A LeardMann, Besa Smith, Edward J Boyko, Tomoko I Hooper, Gary D Gackstetter, Paul D Bliese, Charles W Hoge, and Tyler C Smith, for the Millennium Cohort Study Team (2010-10-15). "Exploratory factor analysis of self-reported symptoms in a large, population-based military cohort". BMC Medical Research Methodology. Kelton et al; licensee BioMed Central Ltd. 10: 94. doi:10.1186/1471-2288-10-94. PMC 2967557. PMID 20950474.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ^ Matt Pueschel (2010-12-29). "Millennium Cohort Study Expanding To Include Spouses of Service Members". Archived from the original on 2016-03-03. Retrieved 2013-08-15.
  24. ^ Karen Jowers (2020-09-10). "Here's your chance to make a difference for the health of the force for the next 50 years". Archived from the original on 2020-09-11. Retrieved 2020-09-11.

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