Insomnia Symptoms Co‐Fluctuate With Depression and Posttraumatic Stress Disorder Symptoms From Pre‐ To 10 Years Post‐Deployment in Military Personnel

Insomnia symptoms are strongly associated with mental health problems such as post-traumatic stress disorder (PTSD) and depression in uniformed personnel, and are often considered a risk factor for adverse post-deployment outcomes. However, the directionality of these relationships remains unclear. This study aimed to disentangle the longitudinal associations between insomnia, PTSD and depression symptoms from pre-deployment up to 10 years post-deployment in military personnel. Data were drawn from the Dutch PRISMO cohort (N = 846 deployed participants) across six timepoints: pre-deployment and 1 month, 6 months, 1 year, 2 years and 10 years post-deployment. Insomnia and depression symptoms were assessed using the corresponding subscales of the Symptom Checklist-90 (SCL-90), and PTSD symptoms with the Self-Rating Inventory for PTSD (SRIP). A random-intercept cross-lagged panel model (RI-CLPM) was applied to separate within-person symptom fluctuations from stable between-person associations. Model fit was good (CFI = 0.99, TLI = 0.98). Between-person correlations among insomnia, PTSD and depression symptoms were high (r = 0.74-0.95). Autoregressive effects were primarily observed in earlier timepoints. Insomnia did not prospectively predict later PTSD or depression symptoms, whereas PTSD and depression symptoms showed small reciprocal cross-lagged effects. Within-time, within-person covariances, that is, the co-fluctuation of symptoms, were significant at all timepoints for all symptom pairs (r = 0.21-0.69). Insomnia, PTSD and depression symptoms show strong and persistent co-fluctuation over time, both within and between individuals. These findings suggest that insomnia co-fluctuates with, but does not causally drive, PTSD and depression symptoms, possibly reflecting shared underlying vulnerability factors.