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Health impact of US military service in a large population-based military cohort: findings of the
Millennium Cohort Study, 2001-2008
Tyler C. Smith, MS, PhD1; Isabel G. Jacobson, MPH1;Tomoko I. Hooper, MD, MPH2;
Cynthia A. LeardMann, MPH1; Edward J. Boyko, MD, MPH3; Besa Smith, MPH, PhD1;
Gary D. Gackstetter DVM, MPH, PhD2,4; Timothy S. Wells, DVM, MPH, PhD1;
Paul J. Amoroso, MD, MPH6; Gregory C. Gray, MD, MPH7; James R. Riddle, DVM, MPH8;
Margaret A. K. Ryan, MD, MPH9; for the Millennium Cohort Study Team
Correspondence to Dr. Tyler C. Smith, DoD Center for Deployment Health Research, Naval Health
Research Center, 140 Sylvester Rd., San Diego, CA 92106-3521, USA; telephone (619) 553-7593;
fax (619) 553-7601; e-mail: [email protected]
Author email addresses
TS: [email protected]
IJ: [email protected]
TH: [email protected]
CL: [email protected]
EB: [email protected]
BS: [email protected]
GG: [email protected]
TW: [email protected]
PA: [email protected]
2
GG: [email protected]
JR: [email protected]
MR: [email protected]
3
ABSTRACT
Background: Combat-intense, lengthy, and multiple deployments in Iraq and Afghanistan have
characterized the new millennium. The US military’s all-volunteer force has never been better
trained and technologically equipped to engage enemy combatants in multiple theaters of
operations. Nonetheless, concerns over potential lasting effects of deployment on long-term health
continue to mount and are yet to be elucidated. This report outlines how findings from the first 7
years of the Millennium Cohort Study have helped to address health concerns related to military
service including deployments.
Methods: The Millennium Cohort Study was designed in the late 1990s to address veteran and
public concerns for the first time using prospectively collected health and behavioral data.
Results: Over 150 000 active-duty, reserve, and National Guard personnel from all service branches
have enrolled, and more than 70% of the first 2 enrollment panels submitted at least 1 follow-up
survey. Approximately half of the Cohort has deployed in support of operations in Iraq and
Afghanistan.
Conclusion: The Millennium Cohort Study is providing prospective data that will guide public
health policymakers for years to come by exploring associations between military exposures and
important health outcomes. Strategic studies aim to identify, reduce, and prevent adverse health
outcomes that may be associated with military service, including those related to deployment.
4
Background
Soon after the end of the 1991 Gulf War, veterans began reporting symptoms and illnesses
they perceived to be possibly related to exposures during deployment. However, research on
illnesses related to the 1991 Gulf War was hampered by the non-availability of objective
measurements on exposures at the individual level, a lack of baseline health data, and an inability to
adequately control for potential confounding factors. Baseline health data prior to potential military
exposures are critical to appropriately evaluate associations between deployment-related exposures
and subsequent health outcomes. Previous research involving cross-sectional and case-control
study designs suffered from recall bias [1], inability to assess temporal association between
exposure and outcome, and lack of the ability to evaluate incident cases of illness or injury and
attributable risk. Thus, the importance of conducting prospective research on questions relevant to
military veterans was clear. Therefore, public health experts and other stakeholders recommended
that the Department of Defense (DoD) establish a cohort to prospectively study both short- and
long-term health effects of military service [1], and this effort was subsequently endorsed by
congress [2, 3]. The Millennium Cohort Study was designed and launched to address this need [3,
4].
Health status is assessed at baseline using self-reported questionnaire data linked to
supplemental data from various DoD administrative and health databases. Follow-up data are
collected every 3 years through postal or Web-based surveys with periodic queries of the same
electronic databases. The launch of the Millennium Cohort Study in July 2001 occurred just prior
to terrorist attacks on the United States on September 11, 2001, and the start of military
mobilization and engagement in multiple combat theaters. Consequently, a significant proportion
of study participants have experienced military deployment, and the stage was set to better
5
understand any health consequences of these deployments.
METHODS
Study Population
The Millennium Cohort Study is a population-based study consisting of participants drawn
from a randomly selected sample of all US military service members on rosters as of October 2000
(Panel 1), October 2003 (Panel 2), and October 2006 (Panel 3) [4, 5]. Panel 1 was a probabilitybased sample of the entire military population. To ensure adequate statistical power to detect rare
health outcomes in smaller subgroups of this first enrollment panel, women, those who had past
deployment experience, and those who were in the reserves or National Guard were oversampled.
Panels 2 and 3 were designed to include newer accessions. Panel 2 included personnel with 1 to 2
years of military service and panel 3 included personnel with 1 to 3 years of military service.
Marine Corps members and women were oversampled in both of these panels. Over 150 000
service members have voluntarily consented and completed baseline questionnaires since the first
wave of invitations in 2001 (July 2001–June 2003; n = 77 047), 2004 (Panel 2 enrolled between
June 2004–February 2006; n = 31 110), and 2007 (Panel 3 enrolled between June 2007–December
2008; n = 43 440), resulting in a 34% cumulative baseline response rate. Over 70% of the first 2
panels have submitted at least 1 follow-up questionnaire.
Demographic and military personnel data from the Defense Manpower Data Center
(DMDC) were obtained for each cohort member. These data include sex, age, marital status,
race/ethnicity, education, service branch (Army, Air Force, Navy/Coast Guard, and Marine Corps),
service component (active duty, Reserve/National Guard), occupation, and military pay grade
(officer, enlisted).
6
Millennium Cohort Foundation Studies
A number of early studies were planned and executed to establish the representativeness of
the Cohort, understand response bias, assess reliability in reporting, ascertain mortality, compare
Web- and paper-based responses, and validate self-reported health outcomes with automated health
information. These foundation analyses have documented a cohort representative of the general US
military, data quality and reliability which are excellent, and little to no evidence of response bias
[4, 6-15].
In order to examine possible response bias, prior hospitalization and ambulatory care
experience of responders was compared with that of nonresponders [6]. Findings demonstrated
that, although there were a few minor differences in health care use, prior health care use did not
appear to influence voluntary participation in the Millennium Cohort Study. In addition, overall
baseline prevalence of mental disorders and functional health compared favorably with other
civilian and military populations [12, 15]. Other foundation studies have addressed characteristics
of subgroups, such as early refusers and early consenters [14] and Internet and paper responders
[10], and demonstrated similarities in demographic and baseline health characteristics. Both
internet and paper responders completed, on average, 98% of the survey questions with no
indication of fatigue bias. Inclusion of a Web-based survey increased data quality and quantity [10,
16], reducing the opportunity for participants to provide unusable data, with minimal likelihood of
enrolling a nonrepresentative group. Added benefits included an informative Web site intended to
foster a relationship with cohort members and to provide a means for updating contact information
[17].
The degree of nonrandom agreement between self-reported Millennium Cohort survey data
7
and electronic records has been examined using Kappa statistics, where a kappa between 0.8–1.0
indicates “greater than substantial agreement,” between 0.6–0.8 “substantial agreement,” between
0.4–0.6 “moderate agreement,” between 0.2–0.4 “fair agreement,” and between 0.0–0.2 “slight or
poor agreement” [18]. Strong reliability was found for anthrax vaccination (κ =.80), smallpox
vaccination (κ = 0.62), deployment status (κ = 0.81), and deployment frequency (κ = 0.72) [9, 11,
13]. While a Kappa value of 0.81 can be interpreted as greater than substantial agreement [18], one
might have expected an even higher Kappa for deployment status (agreement on whether or not a
deployment in support of the operations in Iraq or Afghanistan occurred during the past 3 years).
Perhaps some participants were self-reporting a deployment that occurred during a different time
period or to a location not listed, or in support of another operation. It is also possible that a
participant may have been a member of a special operations unit and therefore unable to reveal their
deployment status. Additionally, in a study of female Cohort members, self-reported occupations
were moderately to highly reliable when compared with electronic occupational data (κ =.65) [8].
Finally, an examination of internal consistency and test-retest reliability of standard health
assessment instruments embedded in the study questionnaire found high internal consistency for 14
of 16 health components [7]. Only alcohol misuse as measured by the PHQ and the CAGE
questionnaires showed low internal consistency, potentially reflecting variability in reporting by
individuals who perceive their behavior as problematic. Substantial test-retest stability was
observed for variables not subject to change such as whether or not the subject was a twin, as well
as variables less likely to change frequently over time, including marital status or education, while
moderate stability was found for more dynamic variables [7].
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Deployment and Deployment-Related Exposures
A major objective when designing the Millennium Cohort Study was to describe
deployment experiences and exposures among US service members and relate them temporally to
subsequent health outcomes. Special emphasis was placed on obtaining information on vaccines,
environmental exposures, and combat-related experiences.
Electronic deployment data are obtained from DMDC and include in- and out-of-theater
dates for current operations. The study questionnaire also uses 24 country and sea codes to assess
self-reported date and location of deployment since 2001.
Table 1 illustrates the demographic and military characteristics of Millennium Cohort
participants by enrollment panel and deployment experience. The demographic makeup of all 3
panels, consistent with the military in general, is composed of a higher proportion of men; enlisted,
active-duty, and Army personnel; and personnel in occupations other than combat. By design,
Panel 1 consists of a cross section of the entire military compared with Panels 2 and 3, consisting of
new accessions. This table also highlights that deployed participants are representative of the total
population in their respective panels, except that a higher proportion of individuals with
deployments to Iraq and Afghanistan between 2001 and 2007 were male, slightly younger, active
duty, and combat specialists.
Among preventive measures used to counter threats of biological warfare agents, most
deployed US service members receive anthrax and smallpox vaccinations. The Anthrax Vaccine
Immunization Program began in the late 1990s, while the smallpox vaccination program began in
2001 [19, 20]. In addition to these electronic vaccination data, questionnaires ask respondents
whether they have ever received the anthrax vaccine, and if so, the number of shots they received.
Beginning with the 2004-2006 survey, the questionnaire also asked whether members received the
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smallpox vaccine after 2001. These data have been used to assess differences between self-reported
vaccination history and electronic records [11, 13], as well as to identify any associated health
differences for concordant or discordant groups [21].
Questions from the National Health Survey of Gulf War Era Veterans [22] were
incorporated into the Millennium Cohort questionnaire to ascertain combat-related exposures and
experiences. Higher rates of posttraumatic stress disorder (PTSD) among US combat infantry
members following deployment to Iraq compared with those deployed to Afghanistan or
nondeployed have been reported [23]. This observation led to a hypothesis that combat experiences
while deployed were more influential predictors of PTSD than deployment per se without exposure
to combat. Data from the Millennium Cohort support increased risk for both PTSD and depression
among study participants who deployed and reported combat exposure [24-27]. To increase our
understanding of any health effects associated with combat exposures, the 2007-2008 questionnaire
was amended to incorporate an additional 13 questions on combat-related experiences. In addition,
questions on significant injuries that included head trauma were also added to support investigations
of mild traumatic brain injury (concussion) [28].
Because deployment may lead to increased risk of exposure to environmental hazards, such
as exposure to pesticides [29, 30], chemical munitions [31, 32], and other environmental exposures,
such as airborne pollutants [33], the questionnaire includes several items to support studies of health
effects associated with environmental exposures. Separate questions relate to potential occupational
hazards requiring the use of personal protective equipment, exposure to dermal hazards, depleted
uranium, microwaves, or insecticides. Cohort members may choose to provide an open-ended
response to share any other physical or psychological exposure of concern.
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Completed, Ongoing, and Future Analyses
The longstanding and continued combat operations in Iraq and Afghanistan have fueled
ongoing concerns among veterans and the general public over unknown exposures and potential
long-term health consequences of serving in the military and, in particular, of deployment. Mental
health disorders and more subtle physical sequelae may affect both short-term and long-term
functional capacity and quality of life in troops returning from deployment. Studies have reported
significantly higher rates of mental health disorders, such as PTSD, major depression, and alcohol
misuse, after deployment in support of combat operations in Iraq and Afghanistan, as well as the
1991 Gulf War and the Vietnam War [23, 34-40]. Findings from the Millennium Cohort Study
describing associations between deployment and mental health and behavioral outcomes have
already informed policymakers who strive to address the needs of veterans [15, 24-27, 41-45].
Results from the Millennium Cohort Study were also cited in a recently published Institute of
Medicine report that identified physical and mental health, as well as readjustment needs, of current
and former service members deployed to Iraq or Afghanistan [46]. Military occupational and
deployment-related stress may manifest in maladaptive coping mechanisms, including smoking,
particularly among those reporting acute and chronic stress [47-49]. Over an average follow-up of
2.7 years, the prevalence of cigarette smoking increased in Millennium Cohort Panel 1 members
when compared with baseline measures [50]. The increase in smoking was greater among those
who deployed than those who did not, with those deploying multiple times or reporting combat
exposures at greatest risk. Increases in smoking postdeployment were predominantly explained by
recidivism among former smokers who had successfully quit prior to deployment. Future
investigations will help determine whether newly initiated or reinitiated smoking following
deployment is temporary or persists over time.
11
Previous cross-sectional and serial cross-sectional studies have reported alcohol misuse
among personnel returning from combat operations in Iraq and Afghanistan [34, 51]. Alcohol use
before and after deployment was also investigated using longitudinal data from this Cohort [43].
Findings revealed that Reserve/Guard personnel who deployed and reported combat exposures were
at increased risk for newly reported heavy weekly drinking, binge drinking, and alcohol-related
problems at follow-up when compared with nondeployed personnel. Only an increased risk of
newly reported binge drinking at follow-up was observed among active-duty personnel who
deployed and also reported combat exposures. As we continue to measure alcohol use among
Cohort participants over time, we will better understand how combat deployments affect alcohol
use.
Investigation of deployment and new-onset disordered eating and changes in weight
between baseline and follow-up surveys showed no differences among men and women who
deployed, with or without combat exposures, and those who did not deploy [25]. When deployers
were examined separately, women with combat exposures were more likely to develop an eating
disorder between baseline and follow-up compared with those who did not experience combat.
Additionally, deployment status did not appear to be associated with weight change between
baseline and follow-up. With the increasing trends of obesity in the United States, continued
evaluation of weight changes over time, including assessment for comorbid conditions and
behavioral characteristics, has great public health implications.
In addition to changes in health risk behaviors possibly associated with deployment-related
stressors, psychiatric disorders, such as depression and PTSD, have also received significant
attention. To investigate depression among Millennium Cohort participants, the study questionnaire
includes a standard self-administered clinical instrument to evaluate mental disorders, the Primary
12
Care Evaluation of Mental Disorders Patient Health Questionnaire [52], and self-reported history of
provider-diagnosed depression. After adjustment, deployment in support of the conflicts in Iraq and
Afghanistan was associated with new-onset depression [24]. Specifically, combat-deployed men
and women were at increased risk of new-onset depression compared with nondeployed men and
women. Conversely, deployment without combat exposures led to decreased risk of new-onset
depression compared with those who did not deploy.
PTSD symptoms have been reported among as many as 30% of veterans following service
in Vietnam and in as many as 10% of personnel returning from the 1991 Gulf War [36, 53-58].
More recent studies using cross-sectional data have indicated that between 6% and 20% of returning
service members screen positive for PTSD [23, 59], and 22% of Iraq and Afghanistan veterans
entering the VA health care system were diagnosed with PTSD [60]. The Millennium Cohort, a
longitudinal study with approximately 50% of its participants deployed in support of the wars in
Iraq and Afghanistan, is well positioned to investigate new onset, persistence, and resolution of
PTSD symptoms among veterans of the current deployments. Recently published findings using
Millennium Cohort data suggest a baseline 2% prevalence of undiagnosed PTSD [41], a 3-fold
increase in new-onset PTSD symptoms or diagnosis among deployed military personnel reporting
combat exposures [27], and a 2-fold higher risk of new-onset PTSD symptoms in both female and
male combat deployers who reported assault prior to deployment [26]. Additional findings from
analyses of Millennium Cohort data suggest that a vulnerable population at increased risk of PTSD
may be identified through predeployment screening [42].
Ongoing prospective investigations are critical to increasing our understanding of PTSD and
include exploring the time course of new-onset and persistent PTSD. Furthermore, identifying and
testing potential interventions to speed recovery and promote resilience in military members facing
13
new challenges is vitally important. Complementary and alternative therapies, physical exercise,
and identification and treatment to minimize effects of mild to severe traumatic brain injury may
mitigate symptoms of PTSD. The 2007-2008 survey cycle added a third longitudinal data point for
further investigation of new onset, persistence, and resolution of PTSD symptoms and offer a better
understanding of resilience factors among cohort members.
Table 2 provides a summary comparison of new-onset behavioral and mental health
outcomes among Panel 1 participants between baseline and first follow-up surveys. Across all
outcomes, the highest proportions were observed among individuals deployed with combat
exposures. It is also notable that smoking recidivism and new-onset binge drinking affected the
highest proportion of participants compared with other outcomes, especially in the youngest age
group. Among mental health outcomes, new-onset depression was most frequently reported among
Cohort members, with the largest proportion occurring among those deployed with combat
exposures, women, and those in the youngest age group.
Increasing evidence suggests that a higher proportion of service members deployed to
Afghanistan and Iraq are suffering from head and brain injuries compared with prior conflicts [61,
62]. These head injuries are due, in part, to widespread use of improvised explosive devices by
enemy combatants. The protection afforded by advanced body armor has allowed head-trauma
patients to survive injuries that may have previously been fatal. Beginning in 2007, questions to
obtain information about head and other injuries were added to the Millennium Cohort survey.
These data will allow Millennium Cohort researchers to study health consequences associated with
mild to severe traumatic brain injury, as well as other injuries sustained in relation to deployment
and occupational exposures.
While injuries remain one of the most significant health problems of the armed services, it is
14
the sequelae of injuries, especially musculoskeletal conditions resulting in permanent disability, that
exact the greatest and most lasting toll on our service members [63]. Musculoskeletal injury-related
disability has been growing rapidly over past decades, as has the cost of care [64], rehabilitation,
and compensation for service-connected disability. The Millennium Cohort Study is uniquely
poised to study the natural history of these chronic conditions among an aging cohort of former
military service members with a variety of musculoskeletal injuries sustained while in service.
Projects currently underway include assessment of service-related injuries associated with mental
health pre- and post-deployment, as well as back pain related to deployment.
Military deployment has previously been identified as a risk factor for deaths due to external
causes in general, and specifically due to motor vehicle crashes, following both the Vietnam War
and the 1991 Gulf War [65-67]. The mechanisms for increased risk of fatal motor vehicle crashes
among returning combat veterans from previous conflicts have yet to be fully understood. Several
pathways for this increased risk have been proposed, including postdeployment mental disorders,
such as PTSD; maladaptive coping mechanisms, such as alcohol misuse following stressful
deployment experiences; increased risk-taking behaviors due to demanding training or combat
experiences; and differentially distributed risk factors among those selected for deployment [66-68].
The Millennium Cohort offers a unique opportunity to prospectively investigate many of these
potential risk factors.
As the Millennium Cohort Study moves toward the end of the first decade of data collection,
longitudinal data points will be used to investigate chronic medical and psychiatric conditions and
any short- or long-term impact of military deployment on the development or natural history of
these conditions. Presence of chronic medical conditions will be identified using several different
methods, including self-reported questionnaire responses and electronic DoD and Department of
15
Veterans Affairs health care databases. Even after separation from military service, the Millennium
Cohort survey instrument will be the main method of assessing new onset of chronic illnesses, since
fewer than 20% of veterans use Veterans Affairs health care facilities. The younger age of the
cohort limits our ability to identify exposure–health outcome associations for common causes of
mortality, such as coronary heart disease or cancer, during early periods of follow-up. However,
chronic conditions with earlier ages of onset should be detectable in relation to exposures of
interest. These include recently investigated conditions such as asthma, hypertension, and diabetes,
as well as planned future investigations of multiple sclerosis, inflammatory bowel disease, and
infectious diseases such as hepatitis C. Similar to incidence estimates for diabetes from the CDC
[69], newly self-reported diabetes in the Millennium Cohort was 3 per 1,000 persons [70], although
risk for diabetes was not associated with combat exposures. Newly-reported hypertension,
however, was found to be associated with reporting multiple combat exposures, especially
witnessing death due to war [45]. Findings from the Cohort also showed that respiratory symptoms
were significantly elevated among Army and Marine Corps personnel deployed in support of the
operations in Iraq and Afghanistan, helping to more clearly define the complicated relationship
between deployment and respiratory health outcomes [44]. Another complex yet important topic of
interest will be reproductive health outcomes in this young adult population [71]. Future analyses
using Cohort data will more clearly define the relationship between deployment and important
health conditions and should shed considerable light on the question of increased disease risk in
relation to common exposures experienced by US military members.
The current study is a population-based, prospective cohort design that allows for baseline
and multiple follow-up assessments on the same individuals. The cohort design, large sample size,
and ability to prospectively follow-up individuals for over 20 years make the Millennium Cohort
16
arguably one of the most ambitious and challenging studies undertaken in the era of modern
epidemiology [72, 73]. However, a study of this size and complexity is not without limitations.
The analyses use self-reported data from questionnaires. Nonetheless, the comprehensive survey
instruments use standardized and validated questions when available and are administered at 3-year
intervals (currently planned through 2022), although the full impact of ongoing conflicts and
detection of more long-term health outcomes will likely require continued follow-up. Although
clinical examinations to confirm self-reported symptoms and conditions were not planned as a part
of this study, self-reported data from questionnaires can be linked with hospitalization discharge
records that include diagnostic codes (providing an indication of disease severity). Previous
comparisons between these self-reported and electronic data sources for specific medical conditions
demonstrated general agreement [74].
Summary and Conclusions
The concept for the Millennium Cohort Study arose from lingering postdeployment
concerns following the 1991 Gulf War [1, 75]. The population-based, prospective longitudinal
design and launching of the baseline cohort just prior to combat operations in Iraq and Afghanistan
were fortuitous and positioned the study to appropriately evaluate the temporal sequence of
exposures and possible health outcomes resulting from military service and deployment without the
substantial limitations of previous observational studies. Prolonged military operations in Iraq and
Afghanistan since 2001 have focused concern on psychological morbidity and its long-term
consequences. The Millennium Cohort Study has baseline data on physical and mental health
status, as well as health-risk behaviors, from a large, population-based military cohort, with
enrollment of the first panel beginning before the current military conflicts and follow-up data
17
based on standard metrics for assessing new-onset health outcomes temporally related to exposures
of concern [4, 5]. The ability to identify high risk groups which are more likely to develop newonset adverse mental health outcomes is of paramount importance and paves the way for more
focused research in this area. Millennium Cohort Study findings on respiratory symptoms and
psychological health outcomes including PTSD, depression, and substance abuse have and should
continue to positively influence policymakers as they address the needs of veterans [12, 15, 24-27,
41-43, 50].
Perhaps most importantly, the Millennium Cohort Study will continue to play an important role
in defining long-term health consequences of military occupational exposures, specifically during
times of combat deployment. Such exposures include psychological and environmental stressors,
medical interventions, and other occupational factors that are unique to military populations [76].
The health outcomes of interest, including chronic diseases, chronic sequelae of injury, and
disability, are clearly of interest to veterans, the general public, and policymakers alike, making the
potential impact of the Millennium Cohort Study far-reaching and unprecedented.
18
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
TS originated the study and supervised all aspects of its implementation. IJ, CL, and BS assisted
with analysis of data. IJ, TH, CL, EB, BS, GG, TW, PA, GG, JR, and MR assisted with design and
interpretation of data, drafting and revision of the manuscript. All authors read and approved the
final manuscript.
Authors’ information
At the time of this study, Tyler Smith, Isabel Jacobson, Cynthia LeardMann, and Besa Smith were
at the Department of Defense Center for Deployment Health Research, Naval Health Research
Center, San Diego, CA. Tomoko Hooper was with the Department of Preventive Medicine and
Biometrics, Uniformed Services University of the Health Sciences, Bethesda, MD. Edward Boyko
was with the Seattle Epidemiologic Research and Information Center, Department of Veterans
Affairs Puget Sound Healthcare System, Seattle, WA. Gary Gackstetter was at Analytic Services,
Inc. (ANSER), Arlington, VA. Timothy Wells and James Riddle were with the Air Force Research
Laboratory, Wright-Patterson Air Force Base, OH. Paul Amoroso was with Madigan Army
Medical Center, Tacoma, WA. Gregory Gray was with the Department of Environmental and
Global Health, College of Public Health and Health Professions, University of Florida, Gainesville,
FL. Margaret Ryan was with the Naval Hospital Camp Pendleton, Camp Pendleton, CA.
19
Acknowledgments
This work represents report 09-14, supported by the Department of Defense, under work
unit no. 60002. The views expressed in this article are those of the authors and do not reflect the
official policy or position of the Department of the Navy, Department of the Army, Department of
the Air Force, Department of Defense, Department of Veterans Affairs, nor the US Government.
All authors certify that they have contributed substantially to: (1) the conception and design
or analysis and interpretation of data, (2) the drafting or revision of the manuscript, and (3) the
approval of the final version. All authors certify that the manuscript represents valid work and that
neither the submitted manuscript nor one with substantially similar content under their authorship
has been published or is being considered for publication elsewhere.
We are indebted to all Millennium Cohort Study participants. We thank Scott L.
Seggermanfrom the Management Information Division, Defense Manpower Data Center, Monterey,
California. Additionally, we thank Millennium Cohort Team Members Melissa Bagnell, MPH;
Gina Creaven, MBA; James Davies; Lacy Farnell; Nisara Granado, MPH, PhD; Gia Gumbs, MPH;
Jaime Horton; Sydney Lee, MS; Travis Leleu; Gordon Lynch; Jamie McGrew; Hope McMaster,
MA, PhD; Amanda Pietrucha, MPH; Teresa Powell, MS; Amber Seelig, MPH; Katherine Snell;
Steven Speigle; Kari Sausedo, MA; Martin White, MPH; James Whitmer; and Charlene Wong,
MPH; from the Department of Deployment Health Research and Michelle LeWark, from the Naval
Health Research Center, San Diego, California. We also thank the professionals from the US Army
Medical Research and Materiel Command, especially those from the Military Operational Medicine
Research Program, Fort Detrick, Maryland. We appreciate the support of the Henry M. Jackson
Foundation for the Advancement of Military Medicine, Rockville, Maryland. VA Puget Sound
provided support for Dr. Boyko’s participation in this research.
20
Human Participation Protection
This study was approved by the Institutional Review Board of the Naval Health Research Center.
This research has been conducted in compliance with all applicable federal regulations governing
the protection of human subjects in research (NHRC Protocol 2000.0007).
21
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Table 1. Characteristics of Millennium Cohort Study Participants by Panel and Deployment Experience
All Participants
N = 77 047
n (%)a
Gender
Male
Female
Birth year
Before 1960
1960-1969
1970-1979
1980 or later
Military rank
Enlisted
Officer
Service component
Reserve/National
Active duty
Service branch
Army
Air Force
Navy
Marine Corps
Military occupation
Combat specialists
Panel 1
2001-2009
Panel 2
All Participants 2001-2009
Panel 3
All Participants
2001-2009
Previous
Deployment
Deployment
Deployment
Deployment
Experienceb
Experiencec
Experienceb
Experienceb
N = 35 564
N = 28 897
N = 31 110
N= 19 598
N = 43 440
N = 27 777
%
%
n (%)a
%
n (%)a
%
56 415 (73.2)
20 632 (26.8)
80.5
19.5
86.7
13.3
19 167 (61.6)
11 943 (38.4)
68.0
32.0
27 941 (64.3)
15 499 (35.7)
71.1
28.9
16 652 (21.6)
29 177 (37.9)
26 672 (34.6)
4546 (5.9)
13.4
39.3
40.6
6.7
18.0
45.7
35.3
1.0
226 (0.7)
1678 (5.4)
9934 (31.9)
19 272 (62.0)
0.6
4.4
29.7
65.4
69 (0.2)
735 (1.7)
6820 (15.7)
35 816 (82.4)
0.1
1.4
15.3
83.3
59 318 (77.0)
17 729 (23.0)
76.8
23.2
78.0
22.0
27 482 (88.3)
3628 (11.7)
88.5
11.5
38 455 (88.5)
4985 (11.5)
88.5
11.5
33 157 (43.0)
43 890 (57.0)
37.3
62.7
25.6
74.4
12 459 (40.1)
18 651 (60.0)
34.9
65.1
8992 (20.7)
34 448 (79.3)
17.0
83.0
36 481 (47.4)
22 357 (29.0)
14 268 (18.5)
3941 (5.1)
49.3
30.2
15.3
5.1
38.5
37.5
19.8
4.3
14 995 (48.2)
8276 (26.6)
5263 (16.9)
2576 (8.3)
54.9
23.5
14.2
7.4
15 798 (36.4)
12 918 (29.7)
7922 (18.2)
6802 (15.7)
40.6
26.8
15.0
17.5
15 425 (20.0)
23.7
24.0
4868 (15.7)
18.9
6591 (15.2)
18.4
33
a
b
c
All others
61 622 (80.0)
76.3
Percentages rounded up and may not sum to 100.
76.0
26 242 (84.4)
81.1
Deployed in support of the Global War on Terrorism between September 1, 2001, and August 31, 2007.
Deployed to the 1991 Gulf War or to Bosnia, Kosovo, or Southwest Asia between 1998 and 2000.
36 849 (84.8)
81.6
34
Table 2. New-onseta behavioral and mental health outcomes in Millennium Cohort Panel 1 participants between baseline and first
follow-up surveys
Health Outcome
Smokingb
Alcohol Usec
New
Smoking
Binge-Like
Problem
Disordered
Smoking
Recidivism
Drinking
Drinking
Eatingd
Depressione
PTSDf
%
%
%
%
%
%
%
Nondeployed
1.4
28.7
18.2
3.7
2.9
5.0
2.3
Deployed without combat
1.5
35.3
20.9
3.2
2.4
2.8
1.4
3.3
44.7
26.2
5.7
3.0
7.3
7.6
Male
1.6
29.5
21.4
4.2
2.6
4.0
2.4
Female
1.7
36.1
15.3
3.0
3.3
8.0
3.8
Recent deployment experienceg
Deployed with combat
exposures
Gender
35
Birth year
Before 1960
0.5
16.6
12.8
2.6
2.5
4.0
2.2
1960-1969
1.1
29.3
19.7
3.0
2.6
4.4
2.3
1970-1979
2.4
49.0
24.4
5.5
3.3
6.2
3.5
1980 or later
8.2
64.0
42.5
10.1
3.6
9.1
5.4
Enlisted
2.1
34.3
21.4
4.5
3.0
5.8
3.3
Officer
0.7
20.0
14.4
2.4
2.4
3.0
1.4
Reserve/National Guard
1.4
28.4
18.0
4.1
2.5
5.1
2.9
Active duty
1.7
33.6
20.4
3.7
3.1
4.9
2.7
Army
2.2
33.6
19.9
4.4
3.0
6.1
3.9
Air Force
1.0
27.2
17.4
2.6
2.3
3.6
1.3
Navy
1.1
29.9
19.9
3.8
3.0
4.6
2.2
Military rank
Service component
Service branch
36
Marine Corps
2.4
38.1
23.8
7.6
3.2
4.1
3.0
Combat specialists
1.4
30.5
21.4
4.2
2.7
3.6
2.4
All others
1.7
31.3
18.8
3.8
2.8
5.3
2.9
Military occupation
a
New-onset was defined among those with no baseline evidence of selected health outcomes.
b
New smoking defined among those with no lifetime history of prior smoking. Smoking recidivism defined among past smokers who
resumed smoking between baseline and follow-up.
c
Binge-like drinking defined as drinking 5 or more drinks (for men) or 4 or more drinks (for women) on at least 1 day of the week, or
any drinking of 5 or more alcoholic beverages on at least 1 occasion during the year. Problem drinking defined by endorsement of at
least 1 item from the Patient Health Questionnaire (PHQ) for probable alcohol abuse [77].
d
Disordered eating defined by criteria from the PHQ[77].
e
Depression defined by criteria from the PHQ-9[77].
f
Posttraumatic stress disorder defined by DSM-IV criteria using the PTSD Checklist-Civilian Version with a score of 50 or more
points [78].
g
Recent deployment was defined as a deployment in support of the wars in Iraq and Afghanistan that occurred between baseline and
follow-up evaluations. Results exclude those who provided either baseline or follow-up information during deployment.
| File Type | application/pdf |
| File Title | The Millennium Cohort Study: Addressing the Long-Term Health Impact of Military Service and Deployment in Support of the Global |
| Author | tyler.c.smith |
| File Modified | 2011-01-26 |
| File Created | 2011-01-26 |