Insomnia as a Risk Factor for Depression: Integrating Cognitive Behavioral Therapy for Insomnia

This review evaluates insomnia as an independent, modifiable risk factor for Major Depressive Disorder (MDD) within primary care, while assessing the efficacy of cognitive behavioral therapy for insomnia (CBT-I) in improving outcomes, preventing onset, and reducing relapse risk of depression. A literature search conducted between January and April 2026 across PubMed, the Cochrane Library, and APA PsycINFO yielded 42 articles published between 2015 and 2026. Applying inclusion criteria focused on adult populations, comorbid insomnia and depression, and clinical outcomes of CBT-I, 26 articles were selected for synthesis. Findings demonstrate that insomnia is a predictive risk factor for MDD onset, persistence, and relapse. Potential mechanistic pathways linking these conditions include neuroinflammatory processes, hypothalamic-pituitary-adrenal (HPA) axis dysregulation, and neurotransmitter imbalances. CBT-I, the first-line treatment for insomnia, produces clinically significant improvements in both sleep and depressive symptoms in those with MDD and insomnia. Evidence shows that early CBT-I reduces the occurrence of MDD in at-risk populations while decreasing relapse rates among remitted patients. Digital CBT-I offers comparable efficacy to in-person therapy, with benefits in scalability, access, and cost-effectiveness, though higher attrition rates remain a concern. Ultimately, early integration of CBT-I into primary care depression management through a stepped-care model addresses some access and utilization barriers. Implementing CBT-I early may reduce overall MDD burden, improve remission rates, and sustain long-term outcomes in patients with comorbid insomnia and depressive symptoms. Future research should prioritize validating stepped-care outcomes in primary care, enhancing digital engagement, and evaluating emerging AI-enhanced digital platforms.