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The US Department of Defense Millennium
Cohort Study: Career Span and Beyond
Longitudinal Follow-Up
Tyler C. Smith, MS, PhD; for the Millennium Cohort
Study Team

C

Objective: To describe current and future career-span health research
in the US Department of Defense Millennium Cohort Study. Methods:
Collaborating with all military service branches and the Department of
Veterans Affairs, the Millennium Cohort Study launched in 2001, before
September 11 and the start of deployments in Afghanistan and Iraq, to
conduct coordinated strategic research to determine any effects of
military occupational and deployment-related exposures, on long-term
health. Results: More than 150,000 consenting members represent demographic, occupational, military, and health characteristics of the US
military. More than 70% of the first two panels have submitted follow-up
questionnaires and ⬎50% have deployed since 2001. Conclusions:
Prospective cohort data have identified subgroups of military populations at
higher risk or more resilient to decrements in mental and physical health.
Continued career span and beyond follow-up will answer long-term health
questions related to military service. (J Occup Environ Med. 2009;51:
1193–1201)

From the Department of Defense Center for Deployment Health Research, Naval Health Research
Center, San Diego, Calif.
Address correspondence to: Tyler C. Smith, MS, PhD, Department of Defense Center for
Deployment Health Research, Naval Health Research Center, 140 Sylvester Road, San Diego, CA
92106-3521; E-mail: [email protected].
Copyright © 2009 by American College of Occupational and Environmental Medicine
DOI: 10.1097/JOM.0b013e3181b73146

ross-sectional and retrospective studies of exposures and health outcomes
are capable of establishing associations but lack a more robust ability to
distinguish exposure contribution in
disease pathways. Causative roles of
exposure to disease are better described through prospective analyses
with appropriate comparison populations where subjects are disease free
at baseline and followed over time to
document exposure and disease
through temporal sequence. Welldesigned prospective cohort studies
may have inferential leverage over
cross-sectional and retrospective
studies through the minimization of
recall and selection biases that are
often influenced by exposure and/or
disease in retrospective or crosssectional assessment of study populations. Well-known prospective
cohort studies, such as the Framingham Heart Study, the British Physicians Study, and others, have made
significant contributions toward improving public health.1–3
Occupational cohort studies are
often defined by a group of workers
in a given occupation classified by
certain exposures encountered on the
job. Occupational cohort studies
have been instrumental in identifying
increased risk of cancer in workers
exposed to gas,4 dyestuff,5 and asbestos6 and increased risk of mortality or
morbidity from other occupational
exposures.7–11 Prospective or historical prospective military cohort studies have also been conducted with
some success in the past but have
largely focused on single exposures.

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These studies have been designed
post exposure, combat deployment,
or conflict and have often lacked
representativeness.6 –9
The Millennium Cohort Study was
envisioned to mitigate these limitations and construct a longitudinal
heterogeneous cohort for comparisons of disease experience across
subgroups defined by military service-related exposures. 10,11 This
large population-based cohort designed in the late 1990s was initiated
in the aftermath of the 1991 Gulf
War after the Department of Defense
(DoD), Congress, and the Institute of
Medicine recommended coordinated
strategic research to determine how
military service, including deployment-related exposures, affect longterm health.12,13 In collaboration
with all military service branches
and the Department of Veterans Affairs (VA), the Millennium Cohort
Study was launched in 2001, before
September 11 and the start of the
wars in Afghanistan and Iraq.10,11
The Cohort includes military service
members from all components (active duty, Reservists, National Guard
members) and all services (Army,
Air Force, Navy, Marine Corps, and
Coast Guard). The objective of this
report is to describe this DoD study,
which follows service members for
the span of their careers and beyond,
and discuss strategic research goals
that will answer health questions pertaining to military service for years
to come.

Materials and Methods
Design and Objectives
The Millennium Cohort Study was
designed in the wake of the 1991
Gulf War to complement many of
the large electronic data that were
beginning to become available to
researchers. This Cohort was constructed to prospectively assess longterm health in all components and
service branches of the US military
and to follow them even after separation from military service with
seven designed 3-year questionnaire

Millennium Cohort Longitudinal Follow-Up

interval assessment periods. The
original objectives of the Millennium
Cohort Study included building a
cohort of ⬃150,000 and assessing
chronic diagnosed and subjective
health problems, including hypertension, diabetes, heart disease, and
chronic multisymptom illnesses
among military members, in relationship to exposures of military concern. The average age of the cohort
at baseline was 28.9 years. The
newer military accessions that were
invited in 2004 and 2007 were randomly selected (oversampling for
women and Marine Corps members)
and designed to complement the
population-based random sample.
More than 150,000 service members
have voluntarily consented and completed baseline questionnaires since
the first wave of invitations in 2001
(July 2001 to June 2003; n ⫽
77,047), 2004 (Panel 2 enrolled between June 2004 and February 2006;
n ⫽ 31,110), and 2007 (Panel 3
enrolled between June 2007 and December 2008; n ⫽ 43,440), resulting
in a 34% cumulative baseline response rate. More than 70% of the
first two panels have submitted at
least one follow-up questionnaire.

Study Population
Cohort composition and survey instruments were designed in 2000. An
initial random sample of active-duty,
Reserve, and National Guard members
from all services was constructed by
the Department of Defense Manpower
Data Center (DMDC) from all US
military personnel serving in October 2000. The study team spent the
remainder of 2000 and the first part
of 2001 conducting a pilot test,
which represented 1% of the original
sample.10,11 The instrument and
methods for conducting the study
were further refined, and the Millennium Cohort Study officially began
enrollment on July 1, 2001. The invited Millennium Cohort Study participants were randomly selected;
however, oversampling of those who
had been previously deployed to
Bosnia, Southwest Asia, or Kosovo

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Smith

(1998 to 2000), Reserve and National
Guard members, and women was conducted to ensure sufficient power to
detect statistical differences in smaller
subgroups of the population.
Demographic and military-specific
data were obtained from electronic
personnel files maintained by
DMDC, including sex, birth date,
highest education level, marital status, race/ethnicity, deployment experience in support of wars in Iraq and
Afghanistan, pay grade (rank of the
service member), service component
(active duty consisting of full-time
military members and Reserve/
National Guard who are mostly citizen soldiers with often full-time employment outside of the US military),
service branch (Army, Air Force,
Navy, Marine Corps, and Coast
Guard), and occupation.

Questionnaire
The questionnaire was designed to
assess medical outcomes and symptoms, chronic multisymptom illnesses,
mental and physical health, physical
activity, sleep, alcohol consumption,
complementary and alternative health
therapies, tobacco use, physical activity, weight change, energy supplementation, family stressors, occupational
stressors, occupational exposures, deployment-specific locations and dates,
deployment-specific exposures, injury,
mild traumatic brain injury, duty and
primary occupation, and reasons for
leaving military service (Table 1).
Multiple standardized instruments are included in the questionnaire, including the posttraumatic
stress disorder (PTSD) ChecklistCivilian Version 14 ; the Patient
Health Questionnaire to assess
depression, panic, anxiety, eating
disorders, and alcohol-related
problems 15–18; the Medical Outcomes study Short Form 36-Item
Health Survey for Veterans to assess
functional health19; and potential
problem drinking assessed using the
CAGE questionnaire.20 These standardized instruments included in the
questionnaire have been shown to be
internally consistent and reliable as

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TABLE 1
Millennium Cohort Questionnaire; 83 Questions With 258 Items
Question Category
Demographics
Contact information, birth year, last 4 digits of social security number, and date survey is
started (6 questions)
Martial status, education, height, and weight (5 questions)
Active military status, and primary and secondary job codes for enlisted, and officer
(3 questions)
Separation from the military (3 questions)
Reasons for separation from the military (1 question with 10 items)
Behavioral
Type of tobacco product (1 questions with 4 items)
Smoking status (5 questions)
Type and quantity of alcoholic beverage (9 questions)
Alcohol abuse (1 question with 5 items; PHQ*)
Problem drinkers (1 question with 4 items; CAGE*)
CAM* treatments (1 question with 12 items)
Supplement use (1 question with 3 items)
Eating disorders (2 questions with 8 total items; PHQ*)
Caffeine and fast food intake (2 questions)
Strength and duration of physical activity (1 question with 3 items; NHIS*)
Daily physical activity and inactivity (2 questions; NHANES*)
Sleep duration (1 question)
Occupational exposures
Personal and environmental exposures (2 questions with 15 total items)
Deployment-related combat exposures (1 question with 13 items)
Location and type of deployment (3 questions)
Anthrax vaccination (1 question with 2 items)
Smallpox vaccination (1 question)
Women’s health
Menstrual period, reasons for not having a menstrual period, symptoms of menstrual
period, child birth, miscarriage, and trouble conceiving (1 question with 7 items)
Mental health assessment
DSM-IV symptoms of PTSD (1 question with 17 items; PCL-C†)
Mental health, emotional role, social function, and vitality (5 questions with 12 total
items; SF-36V†)
Depression, panic, anxiety, risk, physical assault, and medication (7 questions with 41
total items; PHQ*)
Stressful life events (1 question with 11 items)
Symptoms and conditions
Provider-diagnosed general health conditions (1 question with 41 items)
Persistent or recurring health problems (1 question with 19 items)
Somatoform disorder (1 question with 13 items; PHQ*)
Physical functioning, physical role, bodily pain, and general health (7 questions with 18
total items; SF-36V†)
Hospitalization and inability to work or perform usual activities due to illness or injury
(2 questions)
Events that caused serious injuries including head trauma, motor vehicle accident, training,
and combat (2 questions)
Open-ended question to allow for additional health information (1 question)
*PHQ, Primary Care Evaluation of Mental Disorders (PRIME-MD) Patient Health Questionnaire; CAGE, “cut down, annoy, guilty, and eye opener”; CAM, Complementary and
Alternative Medicine; NHIS, National Health Interview Survey; NHANES, National Health and
Nutrition Examination Survey; SF36-V, Short-form health survey.
†
SF-36V, Medical Outcomes Study, Short-Form 36-item questionnaire for Veterans;
PCL-C, Posttraumatic Stress Disorder Patient Checklist, Civilian Version.

measured using Cronbach’s alpha,
indicating an appropriate measurement tool for this population.14
The questionnaire was designed to
take between 30 minutes and 40

minutes with the ability to take it
online or by hard copy mailed
through the US postal service.10
There are 83 questions with multiple
items that comprise the 24-page

1195

questionnaire. Both online and paper
offer the cohort member the ability
to leave the questionnaire and return
to where they left off. The period for
follow-up assessment is 18 months.

Medical Outcomes Assessment
The Millennium Cohort questionnaire assesses 40 health professionaldiagnosed conditions that include
conditions such as hypertension,
heart disease, emphysema, asthma,
hepatitis, hearing loss, sleep apnea,
cancer, depression, and PTSD.21 In
addition to self-reported data, electronic military health data are linked
to include inpatient, outpatient, pharmaceuticals, vaccination information,
and mortality data (Fig. 1) (Granado et
al, unpublished data).21–25 Further,
VA collaboration allows linking of
VA health care and mortality data
after service members leave military
service.26

Millennium Cohort Web Site
The Millennium Cohort Study Team
designed and maintains a highly secure
web site (www.millenniumcohort.org)
capable of being accessed by Cohort
members anywhere Internet access is
available, enhancing the ability to
provide participants with updates on
the study’s progress.10 In addition,
the web site offers a means by which
participants can contact the study
team and update their contact information.27,28 Because of the capabilities of the web site, the study team
was able to implement a bimodal
approach for questionnaire submission by allowing both Web submission in addition to traditional paper
submission. The additional implementation of the web site offered
significant cost savings and higher
quality data. Few or no differences
between Cohort members submitting
paper surveys when compared with
those submitting via the Web have
been found.27

Review and Oversight
The Millennium Cohort Study has
multiple reviews and structured
oversight. Annual review of the

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Millennium Cohort Longitudinal Follow-Up

Support
The study is funded by the Department of Defense through the US
Army Medical Research Materiel
Command (USAMRMC) Military
Operational Medicine Research Program (MOMRP). The Millennium
Cohort Study requires considerable
financial and logistical support that
must be projected and maintained
over the lengthy period of observation. This takes a large and dedicated
staff of professionals who understand the complexities of conducting
a cohort study of this size and who

Smith

continually strive to find ways to
make the process more efficient. The
study is conducted at the Naval
Health Research Center (NHRC) in
San Diego by a multidisciplinary
team of epidemiologists, statisticians, physicians, research assistants,
and data programmers.

of family members. In addition to
assessing changes in job description
through military occupational specialty codes as well as self-reported
job codes, occupational exposures
assessed include jobs requiring protective equipment, routine skin contact with paint and/or solvents,
microwaves, and pesticides. Militaryspecific exposures assessed include
witnessing a person’s death due to
war, disaster, or tragic event; witnessing instances of physical abuse;
seeing dead or decomposing bodies
or prisoners of war; or being exposed
to or provided with countermeasures
for chemical/biological/radiological
(CBR) warfare agents or depleted
uranium. Assessment of exposures
specific to military deployment include feeling in danger of being
killed, being attacked or ambushed,
receiving small-arms fire, clearing
homes or buildings, having an improvised explosive devise explode
nearby, being wounded or injured,
seeing or handling human remains,
knowing someone seriously injured
or killed, having members in unit
seriously injured or killed, and being
directly responsible for death of noncombatants or enemy combatants.

Exposure Metrics

Results

Exposure assessment is important
for hypothesis-driven research as
well as controlling for confounding
that may affect research conclusions.
In health-related studies, it is important
to assess and control for behavioral
exposures. The Millennium Cohort
survey assesses alcohol use, tobacco
use, complementary and alternative
therapies, body mass index, physical
activity, and nutritional supplement
use. It is difficult to completely assess occupational exposures and to
differentiate between those occurring
as a result of one’s occupation and
those occurring in conjunction with
personal nonoccupational settings.
The Millennium Cohort survey assesses personal and family stressors
that include changes in residence, job
changes, suffering sexual or physical
assaults, and death or severe illness

There are more than 150,000 consenting Millennium Cohort members
who represent the US military in
demographic, occupational, military,
and health-related characteristics.
Enrollment and follow-up cycles for
the first panel have resulted in
77,047 completing the initial baseline survey (2001 to 2003), with
55,021 completing the first follow-up (2004 to 2006). Also, as originally designed, the Cohort was later
augmented with 31,110 new accessions (personnel with 1 years to 3
years of service) who completed a
baseline survey between 2004 and
2006, and again with ⬎40,000 new
accessions who completed a baseline
survey between 2007 and 2008.
More than 70% of Cohort members
who submitted baseline data have
submitted a follow-up questionnaire.

Fig. 1. The multiple complementary electronic data sources that are or that may be linked to
Millennium Cohort self-reported data.

study is conducted by the Institutional Review Board at the research
site, the Naval Health Research Center (Protocol NHRC.2000.0007).
Moreover, regular scientific peerreview by the American Institute of
Biological Sciences, DMDC review
of survey content, Office of Management and Budget reviews of science,
Defense Health Board review of science, and a yearly scientific steering
and advisory committee meeting of
leading academicians, veterans service organizations representatives,
and military representatives help to
guide the long-term study.10

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TABLE 2
Characteristics of Millennium Cohort Study Participants and US Military Personnel at 2008

Characteristic

Reserve or National Guarda Reserve or National Guard
Active Dutya
Active Duty US
Millennium Cohort Military Personnel
Millennium Cohort
US Military Personnel in
Members (%)
in 2008b (%)
Members (%)
2008b (%)

Gender
Male
Female
Age, yr
17–24
25–34
35– 44
⬎44
Education
Less than high school diploma
High school diploma diploma/
equivalent
Some college
Bachelor’s degree
Advanced degree
Marital status
Single
Married
Divorced
Race/ethnicity
White non-Hispanic
Black non-Hispanic
Asian/Pacific Islander
Hispanic
Native American
Other/unknown
Operation Iraqi Freedom/
Operation Enduring Freedom
deployment statusb
Deployment experience
No deployment experience
Military pay grade
Enlisted
Officer
Branch of service
Army
Air Force
Navy/Coast Guard
Marine Corps
Occupational category
Combat specialists
Electrical repair
Communications/intelligence
Health care specialists
Other technical
Functional support specialists
Electrical/mechanic
Craft workers
Service support
Students, trainees, other

69.6
30.4

85.8
14.2

65.8
34.2

83.2
16.8

47.8
34.8
15.1
2.3

33.9
40.8
20.8
4.5

29.9
30.3
25.0
14.8

19.3
34.3
20.1
26.3

4.5
64.9

8.8
67.2

15.8
42.6

19.6
53.1

13.0
12.3
5.3

6.1
11.9
6.0

16.9
18.1
6.6

6.1
14.9
6.3

48.6
48.2
3.2

40.5
55.3
4.2

44.8
47.9
7.3

41.1
51.7
7.2

67.5
13.3
8.5
8.0
1.5
1.2

62.8
16.0
4.8
10.3
1.8
4.3

76.3
11.5
3.4
6.8
1.0
1.0

66.4
13.3
3.3
8.4
1.3
7.3

55.0
45.0

56.6
43.4

40.7
59.3

40.4
59.6

84.6
15.4

84.2
15.8

79.1
20.9

82.5
17.5

34.6
30.5
22.8
12.1

37.1
23.1
26.3
13.5

59.7
27.0
10.2
3.1

54.6
21.9
14.3
9.2

18.3
10.3
9.7
10.0
3.3
16.8
17.0
2.8
8.6
3.2

22.4
8.8
8.8
8.2
2.9
16.0
17.2
3.1
9.6
3.0

16.6
6.7
5.6
12.1
2.7
21.9
12.1
4.0
11.2
7.1

17.9
5.2
5.8
7.8
3.1
20.5
13.1
5.1
13.1
8.4

a

Characteristic measured at the time of baseline invitation.
Based on US military rosters as of March 2008 with complete demographic data.
b
Deployment experience recorded as of March 2008.
b

T2

Demographic data for the Cohort are
presented in Table 2. For comparison
purposes of the Cohort to the US
military in general, a snap shot of the

US Military in 2008 is presented in
Table 2 stratified by active duty and
Reserve/National Guard status. At
baseline, the active duty portion of

the Cohort (⬃60%) comprised
⬃70% men, 80% younger than 34
years, 70% with a high school diploma or equivalent, 50% married,

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F2

90% enlisted, 35% Army personnel,
15% combat specialists, and 10%
health care specialists. At baseline,
the Reserve and National Guard portion of the Cohort (⬃40%) comprised ⬃70% men, 60% younger
than 34 years, 55% with a high
school diploma or equivalent, 50%
married, 75% enlisted, 60% Army
personnel, 15% combat specialists,
and 10% health care specialists.
These baseline military and demographic characteristics reasonably
reflect the composition of the US
military in 2008. Although the Cohort is a good reflection of the composition of the US military, there are
noticeable differences in the active
duty Cohort members when compared with active duty in March
2008 with the Cohort comprising
proportionately more women,
younger, educated, single, white
non-Hispanic, Air Force, and with
some deployment experience in
support of the wars in Iraq and
Afghanistan when compared with
the military in general. Moreover,
there are noticeable differences in
the Reserve/Guard Cohort members when compared with all Reserve/Guard in March 2008 with
the Cohort comprising proportionately more women, educated, white
non-Hispanic, and officers than in
the general military.
Investigations have focused on
establishing reliability and representativeness of Cohort data, crosssectional prevalence studies, and
prospective analyses using two data
points in time. Future analyses using
repeated health and exposure assessments will yield a significant and
exponential increase in inferential
capability (Fig. 2). To date, ⬎50% of
the 150,000 Cohort members have
deployed in support of the wars in
Iraq or Afghanistan. Data analyses
have been performed using SAS statistical software version 9.1 (SAS
Institute, Inc., Cary, NC).

Discussion
The Millennium Cohort Study was
created after lessons learned from the

Millennium Cohort Longitudinal Follow-Up

•

Smith

Fig. 2. The planned longitudinal design of the US DoD Millennium Cohort Study until 2022
and the potential temporal increase of research benefit.

1991 Gulf War, which made it
apparent that a well-designed prospective cohort study was critical to
adequately investigate long-term
health consequences associated with
military service. The Cohort allows
for robust comparisons of deployed
and nondeployed, active-duty and
Reserve and National Guard members across all services. Using data
from the Millennium Cohort Study,
recent research has uniquely included active duty, Reserve, and
National Guard members from all
services and focused on comparisons
of populations including deployed
without reported combat exposures,
deployed with reported combat exposures, and nondeployed. Prospective analyses of those deployed in
support of the wars in Iraq and Afghanistan and those not deployed
have answered questions regarding
newly reported respiratory symptoms and conditions (Smith et al,
unpublished data, 2008), hypertension,29 PTSD symptoms,30,31 depression,32 disordered eating,33 newly
reported cigarette smoking,34 and
newly reported problem alcohol
drinking.35
Never before has such a large population-based cohort had the ability
to link to a multitude of electronic
data including inpatient and outpatient health care21,36 pharmaceutical
prescriptions (Granado et al, unpublished data), vaccinations,22–25,37,38
the DoD Birth and Infant Health
Registry,39 the DoD Serum Reposi-

tory,40 mortality while in service and
post service,41 exposure data collected and maintained by the US
Army Center for Health Promotion
and Preventive Medicine,42– 44 contingency/deployment data,45 and VA
health and mortality data26 after separation from military service. These
electronic DoD and VA data allow
for the observation of a full spectrum
of health exposures and outcomes
and significantly strengthens the capability of this longitudinal cohort
study (Fig. 1).
At baseline, the Millennium Cohort Study enrolled and consented
36% of those invited to participate
in the 21-year study.10 Understanding the limitations or potential biases
of this cohort is paramount to longterm inferential capabilities. Concerns
over generalizability, reliability of
self-reported data, and loss to follow-up are inherent in longitudinal
cohort studies caused by these limitations. The Millennium Cohort
study Team has made great efforts to
investigate potential biases. Weights
have been created and employed for
the inverse of the sampling scheme
as well as for the inverse of response
differences with minimal differences
in results.46,47 Analyses have shown
no differential in responder health
with respect to hospitalization and
outpatient encounters in the year
prior to enrollment, suggesting that
prior health did not effect enrollment.36 Reliability of reporting assessed using both test-retest analyses

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and internal consistency investigation of standardized scores,14 and
similar reporting in comparisons of
self-report to electronic vaccination
data,23,24 occupational data,48 and
deployment data has been established.49 Additional analyses have
shown minimal differences between
participants choosing Web submission versus paper submission,27 and
strategies for retention are providing
positive results.28 Although the Millennium Cohort study Team has
worked hard to maximize retention,
which has resulted in a follow-up
rate of ⬎70%, analyses of response
in separated and nonseparated personnel as well as potential responder
bias to follow-up are ongoing.
Current areas of research include
investigations differentiated by deployment focusing on diabetes, weight
change, hearing loss, migraine headaches, unit cohesion, complementary
and alternative medicine and health
care use, complementary and alternative medicine use and mental health
symptoms and diagnoses, physical activity and PTSD symptoms, professional care provider occupations and
PTSD and depression symptoms,
chronic multisymptom illnesses and
associated comorbidities, motor vehicle accidents among deployers, and
mortality.
Future strategic research plans include conducting augmented contact
and focused surveys; neurocognitive
testing of select subsamples of the
Cohort; neuroimaging of select subsamples of the Cohort; biological
sampling using blood/DNA/RNA;
linking to accession data in the Recruit Assessment Program; continuing investigations of biases and loss
to follow-up; longitudinal investigation of effects of multiple deployments on mental and functional
health; longitudinal investigation of
resolution and new onset of mental
health morbidity including PTSD;
longitudinal investigation of resolution and new onset of alcohol use/
misuse; longitudinal evaluation of
new, reuptake, or varied use of tobacco (smoking cigarettes or cigars,

or using smokeless tobacco); longitudinal investigation of mild traumatic brain injury; longitudinal
investigation of respiratory conditions and illnesses; chronic sleeping
deficiencies and mental symptoms;
physical activity and persistence or
resolution of mental health disorders;
investigation of long-term chronic
illnesses, such as diabetes and hypertension, and their impact on military
service; chronic conjunctivitis and
trachoma among deployed service
members; longitudinal assessment of
mortality; parental stress associated
with deployment and birth-related
outcomes; and family unit stress; and
health effects associated with military-unique occupational exposures.
Although the cohort design offers
superior inferential capability over
other observational studies, there are
limitations and strengths that should
be discussed. Limitations to cohort
studies include how generalizable
the responders are to the rest of the
military, self-reporting of symptoms
and reporting of exposures, loss to
follow-up, and rare outcomes that
would not allow the statistical power
to establish exposure to outcome inferences. Strengths to this cohort design include the ability to temporally
investigate an exposure and health
outcome, to detect outcomes with
longer latency, and to ascertain
symptom duration, resolution, and
chronicity of the symptoms and illnesses being measured. Unique to
the Millennium Cohort Study is the
additional strength of being able to
link these data to a wealth of DoD
and VA electronic data that include
personnel files, birth and infant
health, inpatient and outpatient
health care use, pharmaceutical use,
vaccination experience, deployment
experience, exposures, and mortality
(Fig. 1).
Funded by the DoD through the
USAMRMC MOMRP and conducted at NHRC with coinvestigators from all services and the VA,
this large study symbolizes triservice
and VA cooperation needed to effectively assess career-span health out-

1199

comes now and beyond military
service. The uniqueness of this
study’s temporal inception, which allowed launching before September
11, 2001, and the beginning of combat deployments in Afghanistan and
Iraq with continued assessment, will
yield answers to leadership for years
to come. The sustained high operational tempo since September 2001
has been marked by significant combat operations, multiple and often
lengthy deployments, and higher
rates of postdeployment mental
health morbidity associated with
combat deployment.30,50,51 US fighting personnel have never been better
equipped with advanced weaponry
and body armor on the battlefield,
nor has a better strategic long-term
cohort study been implemented to
answer health concerns after service
members return and long after deployments conclude. PTSD, mild
traumatic brain injuries (concussions), and mental health morbidity
remain a significant challenge for
both the service member and the
medical community, potentially for
years to come. The Millennium Cohort Study, currently in its eighth
year, will continue to answer health
concerns now and into the future.

Acknowledgments
This work represents report 08 –38, 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, or the US Government. This research has been conducted in compliance with
all applicable federal regulations governing the
protection of human subjects in research (Protocol NHRC.2000.007).
We are indebted to the Millennium Cohort
Study participants, without whom these analyses would not be possible. In addition to the
authors, the Millennium Cohort Study Team
includes Paul J. Amoroso, MD, MPH, from
the Madigan Army Medical Center, Tacoma,
WA; Edward J. Boyko, MD, MPH, from the
Seattle Epidemiologic Research and Information Center, Veterans Affairs Puget Sound
Health Care System, Seattle, WA; Gary D.

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1200
Gackstetter, DVM, MPH, PhD, from Analytic
Services, Inc. (ANSER), Arlington, VA;
Gregory C. Gray, MD, MPH, from the College of Public Health, University of Iowa,
Iowa City, IA; Tomoko I. Hooper, MD, MPH,
from the Department of Preventive Medicine
and Biometrics, Uniformed Services University of the Health Sciences, Bethesda, MD;
James R. Riddle, DVM, MPH, from the Air
Force Research Laboratory, Wright-Patterson
Air Force Base, OH; Timothy S. Wells,
DVM, MPH, PhD from the Air Force Research Laboratory, Wright-Patterson Air
Force Base, OH; Margaret A. K. Ryan, MD,
MPH, Naval Hospital Camp Pendleton, Occupational Health Department; Lacy Farnell;
Gia Gumbs, MPH; Nisara Granado, MPH,
PhD; Jaime Horton; Isabel Jacobson, MPH;
Kelly Jones; Molly Kelton, MS; Cynthia
LeardMann, MPH; Travis Leleu; Jamie
McGrew; Besa Smith, MPH, PhD; Donald
Sandweiss, MD; Amber Seelig, MPH;
Katherine Snell; Steven Speigle; Kari Welch,
MA; Martin White, MPH; James Whitmer;
and Charlene Wong, MPH; from the Department of Defense Center for Deployment
Health Research, Naval Health Research Center, San Diego, CA.
We thank Scott L. Seggerman and Greg D.
Boyd from the Management Information Division, Defense Manpower Data Center, Seaside, CA. Additionally we thank Michelle
Stoia from the Naval Health Research Center.
We also thank all the professionals from the
US Army Medical Research and Materiel
Command, especially those from the Military
Operational Medicine Research Program,
Fort Detrick, MD. We appreciate the support
of the Henry M. Jackson Foundation for the
Advancement of Military Medicine, Rockville, MD.

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