Trajectories of posttraumatic stress in military peacekeepers: A longitudinal analysis over 23 years

This study investigated trajectories of posttraumatic stress in Norwegian peacekeepers over a 23-year period, focusing on the prevalence and characteristics of late-onset posttraumatic stress disorder (PTSD), where symptoms develop or intensify long after deployment.

We analyzed PTSD symptoms in 463 Norwegian peacekeepers who had deployed to Lebanon as part of the UN peacekeeping mission, UN Interim Force in Lebanon. PTSD symptoms were assessed using the Posttraumatic Symptom Scale-10 at two time points: a median of 7 years (T1) and 29 years (T2) postdeployment. Late-onset PTSD was defined as cases in which peacekeepers did not meet criteria for PTSD at T1 but met the criteria by T2. We used logistic regression to identify predictors of late-onset PTSD, including deployment and postdeployment factors.

Estimated PTSD prevalence increased from 2.8% at T1 to 8.9% at T2, with 8.0% (95% confidence interval [5.5, 10.5]) showing a late-onset trajectory. At T1, those on a late-onset path reported more symptoms than their resilient counterparts. By T2, late-onset cases constituted 90.2% of all PTSD cases. Key predictors of late-onset PTSD included causal attribution of mental health issues to service, OR = 3.03, p < .001; number of deployments, OR = 1.56, p = .039; and postdeployment stressors, OR = 1.30, p = .049.

We found a significant rise in estimated PTSD prevalence among military peacekeepers over two decades, with causal attribution emerging as the strongest predictor of a late-onset trajectory. Interventions aimed at addressing these attributions could be important in mitigating long-term PTSD symptoms. (PsycInfo Database Record (c) 2026 APA, all rights reserved).