IDENTIFYING RISK FACTORS for suicidal behaviors is integral to efforts to prevent suicide among members of the US Armed Forces.1–3 4 , 5 6 7 , 8 9 , 10
Traumatic brain injury (TBI) is a hallmark injury of the Iraq and Afghanistan wars.11 12–14 15 16 17 15
Nonfatal suicidal behaviors can be precursors to suicide death, yet risk factors for the two may differ.2 , 18 19
No prospective study has examined TBI in relation to suicidal behaviors of active-duty service members. Within this population, mental health during and after deployment is of particular concern.20–23 24
The present study evaluates associations of lifetime TBI characteristics with risk of suicide attempt following deployment, using data from the Pre/Post Deployment Study (PPDS) of the Army Study to Assess Risk and Resilience in Servicemembers (Army STARRS).25 26 16 , 27 , 28
We used information from the baseline PPDS survey to characterize age of onset, recency, severity, and number of lifetime TBIs, as well as severity of postconcussive/post-TBI symptoms during the month preceding the index deployment. This report summarizes results of an analysis evaluating each of these factors in relation to risk of suicide attempt from the start of deployment through the next 30 months. Models of associations of lifetime TBI characteristics with suicide attempt adjusted for other baseline risk factors, including sociodemographic and Army career correlates of suicide attempt, as well as lifetime mental disorder.
METHODS
Participants and procedures
The PPDS25 , 29 T 0 ) data were collected 1 to 2 months before the BCTs were deployed to Afghanistan for an average of 10 months. Follow-up data were collected approximately 1 month (T 1 ), 3 months (T 2 ), and 9 months after return from deployment (T 3 ). The T 0 , T 1 , and T 2 surveys were administered in group sessions at soldiers' home posts. The T 3 survey was administered individually, via phone or the Internet, permitting evaluation both of soldiers who remained in service and of those who had separated from the Army. Respondents provided written informed consent to participate in the surveys. Consent to link soldiers' survey responses to their Army/Department of Defense (DoD) administrative records also was requested. Study procedures were approved by the Human Subjects Committees of all collaborating institutions involved in the study.
At baseline, 9949 soldiers were present for duty in the 3 BCTs. Among those present, 9488 (95.4%) consented to participate and 8558 (86.0%) completed the T 0 survey and agreed to linkage of responses to their Army/DoD records. Of those, 7742 were deployed to Afghanistan and were thereby eligible for inclusion in this analysis. However, 61 were excluded for being deployed multiple times before T 3 and 4 were excluded for other reasons (service component other than Regular Army [n = 2], deploying during baseline [n = 1], and lack of administrative records [n = 1]). The final sample included 7677 soldiers, of whom 926 completed only the T 2 survey, 820 completed only the T 3 survey, and 5419 completed both the T 2 and T 3 surveys. Among T 3 respondents, 280 had left Army service, with a mean time out of service of 5.4 months (standard error [SE] = 0.2). There were 26 deaths in the sample, 3 of which were suicides.
Analyses incorporated weights that included propensity-based adjustment for T 0 attrition due to incomplete surveys and inability to link to administrative data (eg, due to the absence of soldier consent). Final values of these weights were poststratified to known demographic and Army service characteristics of soldiers in the 3 BCTs that were deployed to Afghanistan after the T 0 interview dates. Additional details about PPDS design,29 30 31
Measures
Suicide attempt
Soldiers were considered to have had a prospective suicide attempt if they reported any suicide attempt on the PPDS T 2 or T 3 survey. Suicidal behavior was assessed in the T 2 and T 3 surveys using an expanded self-report version of the Columbia Suicide Severity Rating Scale.32 purposefully hurting yourself with at least some intention to die ) at any time during their recent deployment or at any time since returning from their recent deployment.
Soldiers also were considered to have had a prospective suicide attempt if Army/DoD administrative records indicated that any attempt had occurred subsequent to their T 0 survey date. Administrative data sources included (1) records from the Department of Defense Suicide Event Report (DoDSER) and the Army Suicide Event Report (ASER); and (2) ICD-9 (International Classification of Diseases, Ninth Revision ) codes from Military Health System Data Repository (MDR), Theater Medical Data Store (TMDS), and TRANSCOM (Transportation Command) Regulating and Command and Control Evacuating System (TRAC2ES). Among T 0 survey respondents, time to T 3 ranged from 16 to 30 months (median = 21 months). To align with the PPDS follow-up period, administrative records for up to 30 months following the start of the index deployment were considered. Median number of months of records available for a given soldier was 30 months (interquartile range [IQR] = 0; range, 2-30 months), corresponding to a total of 221 234 person-months for the 7677 soldiers in the sample.
Traumatic brain injury PPDS T 0 survey assessment of TBI began with the following probe: How many times in your life (including childhood and adulthood) did you have a head, neck, or blast injury that ... followed by descriptions of alteration of consciousness (AOC; didn't knock you out but caused you to be dazed or “see stars” ), loss of consciousness (LOC; knocked you out ), and posttraumatic amnesia (PTA; caused you to have a lapse in memory of events before, during, or after the injury ). Soldiers indicated how many times they had sustained TBIs with AOC, LOC for less than 30 minutes, LOC for 30 minutes to 24 hours, LOC for more than 24 hours, PTA for less than 30 minutes, PTA for 30 minutes to 24 hours, and PTA for more than 24 hours. Causes of each lifetime injury were not queried in the survey; thus, information was not available regarding whether TBI(s) had occurred during the course of Army service (eg, during previous deployments).
“Probable very mild TBI” was defined as endorsing a head, neck, or blast injury with AOC-only. “Probable mild TBI” was defined as endorsing a head, neck, or blast injury with LOC for up to 30 minutes and/or PTA for up to 30 minutes. “Probable moderate-to-severe TBI” was defined as endorsing a head, neck, or blast injury with LOC for 30 minutes or more and/or PTA lasting 30 minutes or more. Application of these criteria entailed that TBIs classified as very mild or mild aligned with standard definitions of mild TBI; most TBIs classified as moderate-to-severe would fall into higher clinical severity categories. In addition to the number and probable severity of lifetime TBIs, the T 0 survey assessed how recently respondents had experienced TBIs with AOC-only, LOC, and PTA (past 30 days, 1-6 months ago, 7-12 months ago, 1-2 years ago, 3-5 years ago, 6 or more years ago ) and ages at which the first TBIs with AOC-only, LOC, and PTA had occurred.
Postconcussive/post-TBI symptoms
A prior report described derivation of an 8-item Post-Concussive Symptom Scale (PCS-8)33 T 0 survey items assessing past-month frequency of headaches, light sensitivity, noise sensitivity, dizziness/balance problems, irritability, difficulty concentrating, memory problems, and feeling tired/easily fatigued (Cronbach α = 0.88). PCS-8 scores were standardized for the current analysis.
Other somatic symptoms
To evaluate specificity of associations of postconcussive/post-TBI symptoms with suicide attempt, we derived another score to quantify other somatic symptoms at T 0 . The score was based on exploratory factor analysis (EFA) of the entire pool of 18 items assessing past-month somatic symptoms in the T 0 survey. Results supported a 2-factor model (eigenvalues = 10.1, 1.4), with a dominant first factor defined by sleep problems, pain, muscle tension, restlessness, appetite disturbance, and psychomotor retardation, as well as some symptoms assessed by the PCS-8 (memory problems, difficulty concentrating, irritability, headaches, dizziness, feeling tired, and being easily fatigued). To eliminate overlap with the PCS-8, standardized scores on this factor were regressed onto standardized PCS-8 scores and residual values were used as an index of “other somatic symptoms” at T 0 .
Lifetime mental disorder
Lifetime DSM-IV (Diagnostic and Statistical Manual of Mental Disorders , Fourth Edition) mental disorders were assessed at T 0 using survey items adapted from the Composite International Diagnostic Interview screening scales (CIDI-SC)34 35 36
Sociodemographic and Army career characteristics
Sociodemographic and Army career correlates of suicide attempt were identified before estimating associations of TBI characteristics with suicide attempt. The sociodemographic variables considered were age, sex, race/ethnicity, education, marital/relationship status, religious preference, and nativity (self and parents). Army career characteristics included years of Army service, rank, rank below expectation, demotion during the past year, Military Occupational Specialty, deployment history, dwell time, and perceived unit cohesion. Table 1 provides categories and definitions of these variables. The unit cohesion score reflects individual perceptions of cohesion and was based on soldiers' ratings of trust and respect among unit members, respect for unit leaders, treatment of unit members by leaders, discrimination, and morale. EFA of these ratings supported a 1-factor model and internal consistency of the items was high (Cronbach α = 0.89). An overall unit cohesion score was derived by standardizing each rating, summing all 16 standardized ratings, and standardizing the sum.
TABLE 1 -
Distribution and association of sociodemographic and Army career characteristics with any prospective suicide attempt (N = 7677)
a
Bivariate modelsb
Multivariate model: Demographic variables only
Multivariate model: Demographic and Army career variables
%
SE
OR
95% CI
AOR
95% CI
AOR
95% CI
Age at T
0 (median, IQR)
25.0
8.3
0.93
0.89-0.98
0.94
0.90-0.98
0.92
0.87-0.97
Sex
Female
5.1
0.5
1.00
Ref
Male
94.9
0.5
0.42
0.22-0.79
0.41
0.22-0.76
0.40
0.21-0.77
Race/ethnicity
White, non-Hispanic
68.0
0.7
1.00
Ref
Black, non-Hispanic
12.6
0.6
0.89
0.46-1.70
Hispanic
12.1
0.4
1.38
0.76-2.50
Other
7.3
0.3
1.03
0.36-2.91
χ2
3
1.25
P = .74
Education
College graduate or higher
16.2
1.1
1.00
Ref
Some college
3.2
0.2
0.77
0.07-8.23
High school or lessc
80.7
1.1
4.09
1.22-13.76
3.17
1.20-8.41
2.70
1.06-6.91
χ2
2
8.87
P = .012
Marital/current relationship status
Currently married
55.9
0.9
1.00
Ref
Previously married; currently engaged/in serious relationship
4.4
0.2
1.38
0.53-3.58
Previously married; not currently engaged/in serious relationship
5.6
0.4
3.08
1.42-6.66
3.51
1.66-7.41
3.17
1.48-6.81
Never married; currently engaged/in serious relationship
14.0
0.5
0.89
0.50-1.61
Never married; not currently engaged/in serious relationship
20.1
0.7
0.80
0.48-1.36
χ2
4
15.44
P = .004
Religious preference
Protestant
49.8
0.7
1.00
Ref
Catholic
21.1
0.5
1.36
0.72-2.56
Other
4.0
0.2
2.07
0.73-5.87
None
25.2
0.5
1.73
1.14-2.63
1.45
0.99-2.13
χ2
3
7.92
P = .048
Nativity
Soldier and 2 parents born in the United States
79.3
0.6
1.00
Ref
Soldier and 1 parent born in the United States
6.3
0.0
0.89
0.35-2.22
Soldier and 0 parents born in the United States
4.9
0.2
1.59
0.55-4.61
Soldier not born in the United States
9.5
0.4
0.93
0.44-1.97
χ2
3
1.15
P = .76
Rank in Army
Officer
12.8
1.0
1.00
Ref
E1-E4
46.2
1.5
2.07
0.23-18.27
E5-E9
41.1
0.7
2.95
0.37-23.75
χ2
2
3.21
P = .20
Rank below expectation
1.9
0.2
1.05
0.29-3.75
Demoted in past year
1.8
0.2
1.68
0.56-5.10
Years of Army service (median, IQR)
4.1
6.8
1.02
0.94-1.12
Military Occupational Specialty
Combat service support
26.9
1.9
1.00
Ref
Combat arms
59.2
2.5
1.12
0.55-2.26
Combat support
13.9
1.0
1.80
0.92-3.51
χ2
2
5.96
P = .051
Prior deploymentd
No prior deployment
41.6
1.2
1.00
Ref
1.00
Ref
Deployed within the first year of service
11.6
0.4
2.16
1.27-3.68
2.09
1.22-3.56
Deployed, but not in the first year of service
46.8
1.3
1.52
0.92-2.51
1.45
0.90-2.34
χ2
2
9.36
P = .009
8.27
P = .016
Short dwell timee
32.3
0.7
1.28
0.83-1.98
Standardized unit cohesion (mean, SD)
0.00
1.00
0.79
0.65-0.96
0.80
0.66-0.97
Abbreviations: AOR, adjusted odds ratio; CI, confidence interval; IQR, interquartile range; OR, odds ratio; PPDS, Pre/Post Deployment Study; SE, standard error.
a The sample comprised PPDS respondents who completed the predeployment (T 0 ) survey and were subsequently deployed to Afghanistan. The outcome includes any suicide attempt documented in Army/Department of Defense administrative records or reported in the PPDS T 2 or T 3 surveys. All models control for months in administrative data and T 2 /T 3 survey completion. ORs that appear in bold are statistically significant (P < .05); exact P values are provided for χ2 tests.
b Bivariate associations of Army career characteristics with suicide attempt are adjusted for sociodemographic correlates of suicide attempt (age, sex, high school or less education, and marital/relationship status of “previously married, not currently engaged/in a serious relationship”).
c Includes soldiers whose education level was recorded in administrative data as “high school graduate” (n = 5671; 70.4% [SE = 1.0%] of the total sample), “GED or equivalent” (n = 684; 8.6% [SE = 0.4%] of total sample), and “less than high school” (n = 154; 1.7% [SE = 0.2%] of the total sample).
d Number of prior deployments also was considered but was not associated with suicide attempt.
e Short dwell time was defined as “number of months since most recent deployment was less than 2 times the duration of most recent deployment in months.”
Data analysis
Logistic regression was performed to evaluate associations of lifetime TBI variables with prospective suicide attempt. Initial models estimated bivariate associations of lifetime TBI characteristics (age of onset, recency, severity, number) with suicide attempt, controlling for months of administrative data, T 2 /T 3 survey completion, sociodemographic and Army career correlates of suicide attempt, and lifetime mental disorder. Subsequent models were fit adjusting for any lifetime TBI to determine which characteristics of TBI history related to risk of suicide attempt after accounting for effects of any TBI exposure. Results of bivariate models informed construction of multivariable models that estimated joint associations of lifetime TBI characteristics with suicide attempt.
PPDS data are clustered (by BCT and administration session) and weighted; therefore, standard errors were generated using the design-based Taylor series linearization method. Design-based Wald χ2 tests were used to examine multivariate significance. SAS 9.437 P < .05 was considered statistically significant.
RESULTS
Table 1 presents the sociodemographic and Army career characteristics of the sample, which was predominantly male, white, and high school educated. Enlisted soldiers comprised the majority, and most had been deployed at least once prior to the index deployment.
Within the sample, 103 soldiers had 1 or more suicide attempts during the follow-up period (weighted prevalence = 1.31%; SE = 0.14%). Outcome events by mode of data collection are shown in Supplementary Digital Content Table 1 (available at: https://links.lww.com/JHTR/A319 Table 1 ). Adjusting for those characteristics, lifetime mental disorder was associated with an increased risk of prospective suicide attempt (adjusted odds ratio [AOR] = 2.64; 95% CI, 1.76-3.98; P < .001). All subsequent models control for the sociodemographic and Army career correlates of suicide attempt, as well as lifetime mental disorder.
Distribution of lifetime TBI characteristics is summarized in Table 2 . Nearly two-thirds of soldiers had sustained TBI during their lifetimes. In approximately half of these cases, the worst TBI was classified as “mild” and in another third of cases, the worst TBI was classified as “very mild.” Having sustained a single TBI was the exception rather than the norm, with almost a third of the soldiers who endorsed lifetime TBI reporting 5 or more such injuries (median = 2.4; IQR = 3.9). Most soldiers with lifetime TBI reported that their first TBI occurred during childhood or adolescence (median age of first TBI = 13.7 years; IQR = 6.6).
TABLE 2 -
Distribution and association of lifetime TBI characteristics with any prospective suicide attempt
a
Prevalence
Association with suicide attempt (N = 7677)
Overall
Among those with any lifetime TBI
Adjusting for demographic/Army career correlates of SA and lifetime mental disorder
Adjusting for demographic/Army career correlates of SA, lifetime mental disorder, and any lifetime TBI
(N = 7677)
(n = 4808)
%
SE
%
SE
AOR
95% CI
AOR
95% CI
Any very mild TBIb
50.5
0.7
77.9
0.6
0.72
0.44-1.19
Any mild TBIb
37.8
0.7
58.4
0.8
1.14
0.67-1.96
Any moderate-to-severe TBIb
10.1
0.4
15.7
0.6
1.68
0.85-3.35
Any lifetime TBI
64.8
0.7
100
...
0.92
0.56-1.52
Severity of worst lifetime TBI
Never sustained TBI
35.2
0.7
0.0
...
1.00
Ref
Very mild
23.6
0.5
36.4
0.8
0.48
0.25-0.90
1.00
Ref
Mild
31.1
0.7
48.0
0.9
0.97
0.54-1.74
2.02
1.16-3.50
Moderate-to-severe
10.1
0.4
15.7
0.6
1.72
0.86-3.43
3.59
1.64-7.86
χ2
3/2
12.04
P = .007
11.93
P = .003
Age of first TBI (median, IQR)
13.7
6.6
1.01
0.95-1.07
Years since first TBI (median, IQR)
9.5
8.7
0.97
0.92-1.02
Most recent TBI of any severity
Past 12 mo
17.2
0.6
26.6
0.8
1.17
0.63-2.18
1.80
0.82-3.96
1-2 y ago
13.3
0.5
20.6
0.6
1.01
0.57-1.81
1.57
0.73-3.35
3-5 y ago
14.6
0.5
22.6
0.7
0.77
0.37-1.60
1.18
0.55-2.54
6+ y ago
19.6
0.6
30.2
0.9
0.65
0.31-1.38
1.00
Ref
Never sustained TBI
35.2
0.7
1.00
Ref
χ2
4/3
2.99
P = .56
2.96
P = .40
Number of TBIs (median, IQR)
1.0
3.3
2.4
3.9
0
35.2
0.7
1.00
Ref
1
14.9
0.5
23.0
0.8
0.90
0.44-1.85
1.00
Ref
2
13.7
0.4
21.1
0.6
0.65
0.29-1.42
0.72
0.25-2.05
3-4
15.5
0.5
23.9
0.6
0.78
0.40-1.52
0.86
0.43-1.72
5-7
10.4
0.4
16.0
0.7
1.09
0.49-2.40
1.21
0.61-2.39
8+
10.4
0.4
16.0
0.6
1.32
0.68-2.54
1.46
0.71-3.03
χ2
5/4
4.42
P = .49
4.21
P = .38
Symptom severity at T
0
Postconcussive/post-TBI symptoms (mean, SD)
0.0
1.0
1.38
1.09-1.73
1.40
1.12-1.75
Other somatic symptoms (mean, SD)
0.0
0.1
1.12
0.68-1.84
1.12
0.68-1.84
Abbreviations: AOR, adjusted odds ratio; CI, confidence interval; IQR, interquartile range; PPDS, Pre/Post Deployment Study; SA, suicide attempt; SE, standard error; TBI, traumatic brain injury .
a The analysis sample comprised PPDS respondents who completed the predeployment (T 0 ) survey and were deployed to Afghanistan. The outcome includes any SA documented in Army/Department of Defense administrative records or reported in the PPDS T 2 or T 3 surveys. All models control for months in administrative data, T 2 /T 3 survey completion, sociodemographic and Army career correlates of SA (age, sex, high school or less education, marital/relationship status of “previously married, not currently engaged/in a serious relationship,” having deployed within the first year of Army service, and perceived unit cohesion at T 0 ), and lifetime mental disorder at T 0 . AORs that appear in bold are statistically significant (P < .05); exact P values are provided for χ2 tests.
b Model includes additional adjustment for having had TBI(s) of greater or lesser severity; thus, adjusted odds are relative to no lifetime TBI.
Bivariate associations of TBI characteristics with prospective suicide attempt
Results of bivariate models of associations of TBI characteristics with suicide attempt appear in Table 2 . Odds of suicide attempt did not differ for soldiers with versus without any lifetime TBI prior to the index deployment. Soldiers with any very mild TBI, any mild TBI, and any moderate-to-severe TBI also did not differ significantly from those with no lifetime TBI in terms of their risk of suicide attempt. However, the severity of the worst lifetime TBI was associated with odds of suicide attempt (χ2 = 12.04, P = .007). Soldiers whose worst lifetime TBI was very mild had a lower risk of suicide attempt than those with no lifetime TBI (AOR = 0.48; 95% CI, 0.25-0.90; P = .019). Also, after adjusting for any lifetime TBI, those whose worst TBI was mild (AOR = 2.02; 95% CI, 1.16-3.50; P = .010) or moderate-to-severe (AOR = 3.59; 95% CI, 1.64-7.86; P = .001) had a higher risk of suicide attempt than those whose worst TBI was very mild.
Bivariate models also showed that severity of postconcussive/post-TBI symptoms was positively related to risk of suicide attempt, adjusting for other risk factors and any lifetime TBI (AOR = 1.40 [per standard score increase]; 95% CI, 1.12-1.75; P < .001). In contrast, severity of other somatic symptoms was not associated with suicide attempt. Age of onset, recency, and number of lifetime TBIs also lacked significant associations with the outcome (see Table 2 ).
To ensure that collapsing across TBI severity did not obscure effects of age of onset, recency, or number of TBIs, we fit additional bivariate models to examine the associations of TBI characteristics within each severity category. None of the characteristics of very mild TBI history were associated with suicide attempt (see Supplementary Digital Content Table 2, available at: https://links.lww.com/JHTR/A319 2 = 6.26, P = .044; see Supplementary Table 3, available at: https://links.lww.com/JHTR/A319 P = .014) than having had mild TBI more than 5 years before T 0 . Odds of suicide attempt also appeared elevated among those who had sustained mild TBI 1 to 5 years before T 0 (AOR = 1.99; 95% CI, 0.87-4.57; P = .093), but the difference from those who sustained mild TBI more than 5 years before T 0 was not significant. Models adjusting for any mild TBI revealed no significant differences in risk of suicide attempt based on age of onset or number of mild TBIs. Risk of suicide attempt also did not differ on the basis of age of onset or number of moderate-to-severe TBIs (see Supplementary Digital Content Table 4, available at: https://links.lww.com/JHTR/A319 P = .15) relative to those whose most recent moderate-to-severe TBI occurred more than 5 years ago; however, the between-groups difference was not significant.
Multivariable models of associations of TBI characteristics with prospective suicide attempt
Multivariable models were constructed to further evaluate associations of lifetime TBI characteristics with prospective suicide attempt. On the basis of the bivariate model results, dummy variables were used to categorize TBI history first by the severity of the worst lifetime TBI and then, in the case of mild and moderate-to-severe TBI, by how recently an injury of that severity had occurred. The first multivariable model estimated associations of the TBI history categories with suicide attempt. A subsequent model estimated joint associations of TBI history and PCS-8 score. Mean PCS-8 score by TBI history is shown in Figure 1 . Number and weighted prevalence of outcome events by TBI history and PCS-8 score are shown in Table 3 .
Figure 1.: Postconcussive/post-TBI symptom severity by TBI history among PPDS respondents who were deployed to Afghanistan (N = 7677). Both TBI history and past-month postconcussive/post-TBI symptoms were assessed 1 to 2 months prior to the index deployment. a For a subset (n = 435) of soldiers with worst TBI severity of “moderate-to-severe” and any lifetime mild TBI, the survey items did not permit us to distinguish whether the most recent TBI with loss of consciousness and/or memory lapse was mild or moderate-to-severe. Thus, some respondents included in the category “moderate-to-severe TBI in past 5 years” may have had mild TBI(s) in the past 5 years and moderate-to-severe TBI(s) earlier than that. TBI indicates traumatic brain injury ; PCS-8, 8-item Post-Concussive Symptom Scale (theoretical range = 0-32).
TABLE 3 -
Prospective suicide attempt by TBI history and postconcussive/post-TBI symptom severity
Size of subgroup, n (weighted %)
Any prospective suicide attempt within group, n (weighted %)
Overall
7677 (100)
103 (1.31)
TBI history (by worst severity, then recency)
Moderate-to-severe TBI, within past 5 ya
528 (7.1)
20 (3.59)
Moderate-to-severe TBI, 5+ y ago
218 (3.0)
2 (0.83)
Mild TBI, within past year
376 (5.1)
11 (3.19)
Mild TBI, 1-5 y ago
1044 (14.0)
17 (1.59)
Mild TBI, 5+ y ago
876 (12.0)
7 (0.70)
Very mild TBI only
1766 (23.6)
11 (0.57)
No lifetime TBI
2869 (35.2)
35 (1.20)
PCS-8 scoreb
Lowest quartile
1897 (24.1)
12 (0.57)
Low-mid quartile
1745 (22.2)
20 (1.05)
High-mid quartile
2083 (27.5)
24 (1.06)
Highest quartile
1952 (26.2)
47 (2.46)
Abbreviations: PCS-8, 8-item Post-Concussive Symptom Scale; TBI, traumatic brain injury .
a For a subset (n = 435) of respondents with worst TBI severity of “moderate-to-severe” and any lifetime mild TBI, the survey items did not permit us to distinguish whether the most recent TBI with loss of consciousness and/or memory lapse was mild or moderate-to-severe. Thus, some respondents included in this category may have had mild TBI(s) in the past 5 years and moderate-to-severe TBI(s) earlier than that.
b Although quartiles are presented in this table, the continuous PCS-8 score was used in all regression models.
In multivariable model 1 (see Table 4 ), TBI history of “very mild only” was associated with a reduced risk of suicide attempt relative to no lifetime TBI (AOR = 0.48; 95% CI, 0.26-0.90; P = .019). In addition, the association of moderate-to-severe TBI history with suicide attempt approached significance (χ2 2 = 5.33, P = .070). Soldiers with moderate-to-severe TBI in the past 5 years exhibited approximately twice the odds of suicide attempt of soldiers with no lifetime TBI (AOR = 2.08; 95% CI, 1.02-4.24; P = .039).
TABLE 4 -
Associations of TBI history and postconcussive/post-TBI symptoms with prospective suicide attempt (N = 7677)
a
Association with any prospective suicide attempt
Multivariable model 1
Multivariable model 2
AOR
95% CI
AOR
95% CI
TBI history (by worst severity, then recency)
Moderate-to-severe TBI
Most recent within past 5 yb
2.08
(1.02-4.24)
1.72
(0.86-3.45)
Most recent 5+ y ago
0.66
(0.14-3.26)
0.63
(0.13-2.99)
χ2
2
5.33
P = .07
3.15
P = .21
Mild TBI
Most recent within past year
1.80
(0.74-4.35)
1.54
(0.63-3.78)
Most recent 1-5 y ago
0.99
(0.47-1.82)
0.81
(0.41-1.61)
Most recent 5+ y ago
0.58
(0.25-1.31)
0.55
(0.24-1.26)
χ2
3
4.88
P = .18
4.77
P = .19
Very mild TBI only
0.48
(0.26-0.90)
0.45
(0.24-0.85)
No lifetime TBI
1.00
Ref
1.00
Ref
Symptom severity at T
0
Postconcussive/post-TBI symptoms (mean, SD)
1.31
(1.05-1.63)
Abbreviation: AOR, adjusted odds ratio; CI, confidence interval; PPDS, Pre/Post Deployment Study; TBI, traumatic brain injury .
a The sample comprised PPDS respondents who completed the predeployment (T 0 ) survey and were deployed to Afghanistan. The outcome includes any suicide attempt documented in Army administrative data or reported in the PPDS T 2 or T 3 surveys. All models control for months in administrative data, T 2 /T 3 survey completion, sociodemographic and Army career correlates of suicide attempt (age, sex, high school or less education, marital/relationship status of “previously married, not currently engaged/in a serious relationship,” having deployed within the first year of Army service, and perceived unit cohesion at T 0 ), and lifetime mental disorder at T 0 . AORs that appear in bold are statistically significant (P < .05); exact P values are provided for χ2 tests.
b For a subset (n = 435) of respondents with worst TBI severity of “moderate-to-severe” and any lifetime mild TBI, the survey items did not permit us to distinguish whether the most recent TBI with loss of consciousness and/or memory lapse was mild or moderate-to-severe. Thus, some respondents included in this category may have had mild TBI(s) in the past 5 years and moderate-to-severe TBI(s) earlier than that.
Multivariable model 2 included both TBI history and postconcussive/post-TBI symptom severity as predictors (see Table 4 ). PCS-8 score was positively associated with odds of suicide attempt (AOR = 1.31; 95% CI, 1.05-1.63; P = .012), and TBI history of “very mild only” remained associated with reduced risk of suicide attempt compared with no lifetime TBI (AOR = 0.45; 95% CI, 0.24-0.85; P = .012). However, soldiers with moderate-to-severe TBI in the past 5 years no longer displayed significantly higher odds of suicide attempt than those with no lifetime TBI. Post-TBI symptoms thus appeared to explain the association of past-5-year moderate-to-severe TBI with prospective suicide attempt. Notably, attenuation of that association was not observed (AORΔ = −0.01; see Supplementary Digital Content Table 5, available at: https://links.lww.com/JHTR/A319 2 6 = 5.94, P = .43). Thus, multivariable model 2 was accepted as the final model.
DISCUSSION
This study is the first to prospectively evaluate associations of lifetime TBI characteristics with suicide attempt following military deployment and the first to consider postconcussive/post-TBI symptoms as a risk factor for suicidal behavior. Amid a range of current and historical TBI characteristics assessed in the predeployment survey, only past-month postconcussive/post-TBI symptoms were associated with an increased risk of prospective suicide attempt. This association was observed in the presence of controls for lifetime mental disorder and sociodemographic/Army career correlates of suicide attempt.
The current results imply that detection of postconcussive/post-TBI symptoms could help identify at-risk soldiers and thus facilitate targeting of Army suicide prevention programs. Surveillance of these symptoms would also yield opportunities for treatment38
An unexpected finding was that soldiers with “very mild TBI only” had decreased odds of suicide attempt relative to soldiers with no lifetime TBI. A history of very mild TBI could indicate greater involvement in sports or vigorous physical activity, which are inversely associated with hopelessness and suicidal behavior among adolescents.39–41
The seemingly elevated risk of suicide attempt among soldiers who had sustained moderate-to-severe TBI within 5 years of the index deployment was largely explained by post-TBI symptoms. Evidence from the analysis further suggested that this association was mediated by post-TBI symptoms specifically, as opposed to somatic symptoms in general. While this provides indirect evidence of a link between TBI and the symptoms assessed by the PCS-8, we acknowledge that such symptoms can also result from other medical conditions and mental disorders. TBI history did not interact with PCS-8 score to predict suicide attempt, suggesting that for the purpose of suicide risk assessment, screening can focus primarily on the severity of recent postconcussive/post-TBI symptoms (as opposed to the specifics of TBI history). However, future studies should continue to investigate possible interaction effects of TBI history and postconcussive/post-TBI symptoms on risk of suicide attempt, as our study may not have been adequately powered to detect significant interactions.
Approximately 1.3% of soldiers made a suicide attempt over an average follow-up period of 30 months, according to their own report or administrative records. The 2014 National Survey on Drug Use and Health found that the past-year prevalence of suicide attempt among US adults was 0.5% overall and 1.2% among young adults (aged 18-25 years).42
The relatively low concordance of self-report and administrative suicide attempt data was not unexpected. Other investigators43 T 3 assessment would not be captured via self-report. We also expected some self-reported attempts to be absent from Army/DoD records, as medical or mental health services are not sought in all cases of suicide attempt. Some administratively documented suicide attempts may not have been disclosed on surveys due to fear of adverse consequences or stigma.
Our results must be considered alongside several limitations. Retrospective self-report data are vulnerable to response and recall biases. With respect to TBI assessment, very mild TBIs might not be remembered or considered important enough to report, resulting in underestimation of the occurrence or number of TBIs. Severity of TBIs also might be misjudged if respondents did not accurately remember how long periods of LOC or PTA had lasted. While we acknowledge the limitations inherent in self-assessment, more lifetime injuries are likely to be captured with this mode of assessment than with reliance on medical record data.44
The baseline PPDS survey did not collect information about circumstances surrounding each TBI; thus, we were unable to estimate the proportion of lifetime TBIs that occurred during previous deployments/Army service. In addition, we sought to identify risk factors for suicide attempt that could be detected before soldiers were deployed; consequently, the analysis did not consider the effects of TBI(s) sustained during or after return from the index deployment. These are important topics for future investigation.
A final limitation of the TBI assessment was that items evaluating age of onset and recency of TBI with LOC and PTA did not contain duration specifiers. Thus, for some cases in which both mild TBI and moderate-to-severe TBI were reported, we could not determine whether the injury of reference for the age of onset and recency questions was mild or moderate-to-severe. The main impact was that, in the final model, we may have overestimated the prevalence of moderate-to-severe TBI in the past 5 years (ie, some of those injuries could have been mild TBIs, and the soldier's moderate-to-severe TBI(s) could have occurred earlier). The PPDS survey items otherwise provided a very high degree of granularity with respect to characterization of respondents' TBI histories.
It is conceivable that soldiers who sustained more severe injuries during the index deployment (including TBIs) were less likely to complete the T 2 and T 3 surveys. Concerns about underrepresentation of this subgroup in the analysis are partly mitigated by the availability of another source of suicide attempt outcome data (ie, Army/DoD administrative records). Finally, suicide attempt and suicide death have different base rates and correlates.2 , 18
In conclusion, predeployment postconcussive/post-TBI symptoms were associated with an increased risk of suicide attempt among soldiers who were deployed to Afghanistan. Detection of postconcussive/post-TBI symptoms may facilitate both targeting of suicide prevention programs and timely intervention to alleviate potentially distressing and disabling symptoms. Future research should investigate mechanisms underlying the association of postconcussive/post-TBI symptoms with suicide attempt, as well as effects of treatment of these symptoms on the mental health outcomes of deployed service members.
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