Association of Combat Experiences With Suicide Attempts Among Active-Duty US Service Members

IMPORTANCE: There is uncertainty about the role that military deployment experiences play in suicide-related outcomes. Most previous research has defined combat experiences broadly, and a limited number of cross-sectional studies have examined the association between specific combat exposure (eg, killing) and suicide-related outcomes. OBJECTIVE: To prospectively examine combat exposures associated with suicide attempts among active-duty US service members while accounting for demographic, military-specific, and mental health factors. DESIGN, SETTING, AND PARTICIPANTS: This cohort study analyzed data from the Millennium Cohort Study, an ongoing prospective longitudinal study of US service members from all military branches. Participants were enrolled in 4 phases from July 1, 2001, to April 4, 2013, and completed a self-administered survey at enrollment and every 3 to 5 years thereafter. The population for the present study was restricted to active-duty service members from the first 4 enrollment phases who deployed in support of the wars in Iraq and Afghanistan. Questionnaire data were linked with medical encounter data through September 30, 2015. Data analyses were conducted from January 10, 2017, to December 14, 2020. EXPOSURES: Combat exposure was examined in 3 ways (any combat experience, overall combat severity, and 13 individual combat experiences) using a 13-item self-reported combat measure. MAIN OUTCOMES AND MEASURES: Suicide attempts were identified from military electronic hospitalization and ambulatory medical encounter data using the International Classification of Diseases, Ninth Revision codes. RESULTS: Among 57 841 participants, 44 062 were men (76.2%) and 42 095 were non-Hispanic White individuals (72.8%), and the mean (SD) age was 26.9 (5.3) years. During a mean (SD) follow-up period of 5.6 (4.0) years, 235 participants had a suicide attempt (0.4%). Combat exposure, defined broadly, was not associated with suicide attempts in Cox proportional hazards time-to-event regression models after adjustments for demographic and military-specific factors; high combat severity and certain individual combat experiences were associated with an increased risk for suicide attempts. However, these associations were mostly accounted for by mental disorders, especially posttraumatic stress disorder. After adjustment for mental disorders, combat experiences with significant association with suicide attempts included being attacked or ambushed (hazard ratio [HR], 1.55; 95% CI, 1.16-2.06), seeing dead bodies or human remains (HR, 1.34; 95% CI, 1.01-1.78), and being directly responsible for the death of a noncombatant (HR, 1.81; 95% CI, 1.04-3.16). CONCLUSIONS AND RELEVANCE: This study suggests that deployed service members who experience high levels of combat or are exposed to certain types of combat experiences (involving unexpected events or those that challenge moral or ethical norms) may be at an increased risk of a suicide attempt, either directly or mediated through a mental disorder.