Does Insomnia Treatment Prevent Depression?

Rates of Major Depressive Disorder (MDD) are increasing globally, in part due to the COVID-19 pandemic, contributing to disease burden. It has long been known that insomnia is intricately connected with depression as indicated by greater depression severity and lower treatment response. Further, insomnia is a significant risk factor for new onset depression. Treatment of insomnia is thus a logical target for prevention of incident and recurrent MDD. This systematic review sought to evaluate the current evidence for the preventive effects of insomnia treatment on depression onset. A database search yielded 186 studies, six of which met criteria for inclusion in this review. All of the studies utilized Cognitive Behavioral Treatment for Insomnia (CBT-I) as the target intervention and most delivered treatment via a digital platform. Four of the studies found significantly lower rates of MDD onset in those who received CBT-I compared to a control condition. The two remaining studies failed to confirm these effects in primary analyses but secondary analyses suggested evidence of a preventive effect. There was significant methodologic heterogeneity across studies in terms of sample selection, outcomes, and follow-up periods, limiting the ability to draw firm conclusions. The evidence overall is in the direction of insomnia treatment reducing the risk for onset of MDD, but further research is warranted.