Risk factors for firearm suicide and non-firearm suicide among former US service members

The Lancet Regional Health  | 2024 Vol. 36, p. 1-14

Prospective comparison of risk factors for firearm suicide and non-firearm suicide in. a large population-based cohort of current and former US service members: findings from the Millenium Cohort Study

Cynthia A. LeardMann; Deployment Health Research Department, Naval Health Research Center, San Diego, CA, USA; Leidos, Inc., San Diego, CA, USA

Neika Sharifian; Deployment Health Research Department, Naval Health Research Center, San Diego, CA, USA; Leidos, Inc., San Diego, CA, USA

Steven Warner; Deployment Health Research Department, Naval Health Research Center, San Diego, CA, USA; Leidos, Inc., San Diego, CA, USA

Edward J. Boyko; Seattle Epidemiologic Research and Information Center, Department of Veterans Affairs Puget Sound Health Care System, Seattle, WA, USA; Department of Epidemiology, University of Washington School of Public Health, Seattle, WA, USA; Department of Medicine, University of Washington School of Medicine, Seattle, WA, USA

Satbir K. Boparai; Deployment Health Research Department, Naval Health Research Center, San Diego, CA, USA; Leidos, Inc., San Diego, CA, USA

Teresa M. Powell; The Informatics Applications Group, Reston, VA, USA

Rudolph P. Rull; Deployment Health Research Department, Naval Health Research Center, San Diego, CA, USA

Mark A. Reger; Veterans Affairs Puget Sound Health Care System, Seattle, WA, USA; Department of Psychiatry & Behavioral Sciences, University of Washington, Seattle, WA, USA

Charles W. Hoge; Center for Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, MD, USA; Office of the Army Surgeon General, Falls Church, VA, USA

Background: Suicide is a leading cause of death among service members and veterans. Among suicide methods, firearms are the most lethal and commonly used method among military populations. Limited research has compared risk factors for the various suicide methods. This study evaluated and compared risk factors for firearm versus non-firearm suicides using data from the Millennium Cohort Study, a large longitudinal military cohort. 

Methods: Using a competing risk approach, we identified factors associated with each suicide method. Risk factors included demographics, mental health diagnoses, mental health symptoms, military-specific characteristics, health behaviors, and psychosocial factors. Cause of death was assessed from July 1, 2001, through December 31, 2018. 

Findings: Among 201,565 eligible participants with a mean [SD] age of 29.0 [58.1] years, there were 139,789 (69.3%) male, 61,776 (30.7%) female, 15,927 (7.9%) Hispanic, 24,667 (12.3%) non-Hispanic Black, 14,138 (7.0%) Asian, Pacific Islander, American Indian or Multiracial, and 146,736 (72.8%) non-Hispanic White participants. During the study period, 330 died by firearm suicide and 168 died by non-firearm suicide. Overall, effect estimates for risk factors were similar across both methods of suicide. After adjustment, men (HR: 3.69, 95% CI: 2.59, 5.24) and those who screened positive for depression (HR: 1.97, 95% CI: 1.36, 2.87) had an elevated risk for firearm suicide. In contrast, those who self-reported a history of bipolar diagnosis (HR: 3.40, 95% CI: 1.76, 6.55) had significantly increased risk for non-firearm suicide.

Interpretation: Findings suggest that prevention and intervention strategies overall may not be differentiated by specific demographic, military, or health factors. Targeted interventions that consider sex and mental health screens might have relative utility in preventing firearm-related suicide risk compared with non-firearm suicide. 

Cohort studies; veterans; suicide; depression; mental health; risk factors; health behavior

“Suicide is a current public health concern among military service members and veterans." Despite national prevention efforts, "annual rates among service members and veterans (i.e., 24.3 suicides per 100,000 active component service members in 2021; 31.7 per 100,000 veterans in 2020) have risen significantly in the last 20 years." Firearms are the most common method of suicide in military populations, as "approximately two-thirds of suicides among service members and veterans are by firearm whereas only half of all suicides in the US general population are by firearm." Prior studies have shown that "individuals with mental health diagnoses were less likely to die by a firearm suicide compared with non-firearm suicide; however, this analysis excluded studies conducted in the context of military conflicts." Other research has identified that "risk factors previously found to be associated with firearm suicide compared with non-firearm suicide among civilians include male sex, non-Hispanic White race and ethnicity, older age, and being married." The study aims to address gaps in the literature by prospectively comparing risk factors for firearm and non-firearm suicides among US military personnel and veterans (p. 2). 

“This study expands on the existing body of research by analyzing prospective data from a large cohort of US service members." The objective was to "evaluate and compare risk factors for firearm suicide versus non-firearm suicide, including demographics, mental health diagnoses, mental health symptoms, military-specific characteristics, health behaviors, and psychosocial factors." The Millennium Cohort Study "is the largest and longest-running longitudinal study designed to examine the long-term health effects of military service." Data were collected from "201,565 service members from the first four panels who completed a baseline survey." Cause of death was determined using "the Armed Forces Health Surveillance Division (AFHSD) Defense Medical Surveillance System (DMSS) and the Department of Defense and Veteran Affairs Suicide Data Repository (SDR)." The study employed "cause-specific Cox proportional hazards regression models, a competing risk approach that accounts for length of time to the event (suicide), to identify factors associated with each suicide method” (p. 4).

“During the study period, 330 died by firearm suicide and 168 died by non-firearm suicide." The results indicated that "men had a significantly higher risk of firearm suicide compared with non-firearm suicide" with a hazard ratio (HR) of "3.69 (95% CI: 2.59, 5.24)." Participants who "self-reported a history of bipolar diagnosis (HR: 3.40, 95% CI: 1.76, 6.55) had significantly increased risk for non-firearm suicide." In contrast, "self-reported depression symptoms increased the risk for firearm suicide (HR: 1.97, 95% CI: 1.36, 2.87)." Military characteristics such as "enlisted rank (compared with officers), serving in the Army or Marine Corps (compared with Air Force), and previous deployment with combat experience" were associated with increased risk for both methods. Among psychosocial factors, smoking, alcohol-related problems, life stressors, and lack of social support “were associated with elevated risks of both firearm and non-firearm suicide” (p. 5). 

Overall, "findings underscore that there are far more similarities in a large array of risk factors by suicide method than differences." While previous research suggested that "those with mental health diagnoses were more likely to die by non-firearm suicide," this study found that "self-reported mental health symptoms increased the risk of firearm suicide, while these associations were not as strong nor consistent for non-firearm suicide." The authors note that "those who died by firearm suicide were more likely to be experiencing mental health symptoms but less likely to seek help for those symptoms." This supports previous research showing that "those who died by firearm suicide were less likely to seek mental health treatment and more likely to die on their first suicide attempt" (p. 11).

The study concludes that "suicide prevention strategies and intervention efforts focused on a specific suicide method may not need to be differentiated by specific demographic, military, or health factors." However, "since firearms are the most lethal and commonly used method among service members and veterans, focusing efforts on safe firearm storage practices, lethal means safety, and counseling to prevent suicides due to firearms may increase the probability of long-term survival for service members and veterans” (p. 11).

“With limited exceptions, suicide prevention strategies and intervention efforts focused on a specific suicide method may not need to be differentiated by specific demographic, military, or health factors in military populations. Nonetheless, as firearms are the most lethal and commonly used method, efforts focused on safe firearm storage practices and lethal means safety may decrease the probability of suicide among current and former service members” (p. 2).

“Due to the lower numbers of non-firearm suicides compared with firearm suicides, there was reduced power for identifying risk factors for non-firearm suicides. Furthermore, we could not disaggregate non-firearm suicides into more specific categories nor conduct sex or ethnic-specific analyses. Additionally, although the current study’s sample size was sufficient to precisely estimate a multitude of risk factors for this rare event, some estimates, such as a history of bipolar disorder diagnosis, were estimated with less precision due to the low frequency of bipolar diagnoses within the study population. Another limitation was that other potential risks and protective factors for suicide were not assessed, including, gender identity, traumatic brain injury, burdensomeness, belongingness, and history of other mental health diagnoses (e.g., anxiety). We were not able to assess suicidal ideation, as this item was only available at baseline for the first three panels; it was removed in subsequent survey cycles based on requirements from the Institutional Review Board. Further, there were no data on ownership/access, familiarity with, and/or storage of firearms. However, data for some of these constructs, such as suicidal behaviors, firearm access, firearm storage, and gender identity, are starting to be collected on the Millennium Cohort survey. Non-firearm suicides may be underestimated due to misreporting deaths due to overdose or injury as accidental; however, it is unknown whether different risk

factors pertain to these deaths. Most of the risk factors were based on self-reported baseline survey data. Social support was based on one item and may not fully capture the desired construct. These data do not necessarily capture changes in the health status, diagnoses in medical records, or behaviors of participants that may have occurred over the years and closer to the time of death. Further, nonresponse differed by age, sex, race and ethnicity; however, these differences were small, and prior investigations have found that nonresponse did not substantially change estimates of health outcomes. 33 The cause-specific method has some built-in selection bias and assumptions that may not have been fully met, including measuring all common risk factors, time-at-risk of suicide began at the study start time, and exchangeability of censoring. Lastly, the data are from an observational study, and thus unmeasured confounding may have biased the effect estimates” (p. 12).