Insomnia Symptom Improvement as a Mediator for Mental Health Symptom Reduction Following Behavioral Insomnia Treatment Among Women Veterans.

Cognitive-behavioral therapy for insomnia (CBT-I) improves comorbid mental health symptoms (depression, anxiety, and posttraumatic stress disorder [PTSD]), with sleep improvements hypothesized as the mechanism for the observed improvements. This study examined change in insomnia severity as a mediator of mental health symptom improvements in women veterans following behavioral insomnia treatment. Secondary analysis was conducted using data from a comparative effectiveness trial that evaluated insomnia outcomes in women veterans following CBT-I and an acceptance and commitment therapy-informed insomnia (ABC-I) treatment. The treatments were statistically equivalent in improving sleep, so were combined for the current analyses. The sample included 149 middle-age women veterans of diverse race and ethnicity (mean age 48 years, 34.2% White, 26.9% Black or African American, 18.8% Hispanic/Latinx). Variables of interest included insomnia severity (Insomnia Severity Index), and measures of depression (Patient Health Questionnaire-9) and generalized anxiety (Generalized Anxiety Disorder-7). A generalized structural equations model was conducted to test study hypotheses. Study treatment phase (baseline, posttreatment, 3-month follow-up) significantly predicted depression (-3.95 ≤ b ≤ -4.35, p < .001) and anxiety (-4.29 ≤ b ≤ -4.75, p < .001) symptom improvement in nonmediation models. Insomnia severity mediated improvement in depression and anxiety symptoms (0.515 ≤ b ≤ 0.584, p < .001), with change in insomnia severity accounting for 88%-97% of depression and anxiety symptom reduction following insomnia-focused behavioral psychotherapies. This study identified reduction in insomnia severity as a major mechanism of improvement in depression and anxiety symptoms following behavioral insomnia treatment. Findings also reinforce the value of insomnia-focused behavioral psychotherapies in patients with comorbid mental health conditions.