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.