Sleep Disturbances and Depression: A Narrative Review of the Bidirectional Relationship, Mechanisms, and the Role of Physical Activity

Abstract

Introduction and aim: Depression and sleep disturbances are common conditions that frequently co-occur and contribute substantially to the global burden of disease. This review summarizes current evidence on their bidirectional relationship and the role of physical activity as a modifiable therapeutic factor. Material and methods: A narrative review of studies indexed in PubMed, Scopus, and Google Scholar was conducted. Epidemiological, longitudinal, mechanistic, and interventional studies, including systematic reviews and meta-analysis, were analyzed. Results: Insomnia is a consistent predictor of future depression, while depression negatively affects sleep quality, supporting a reciprocal relationship. Shared mechanisms include altered sleep architecture, REM sleep abnormalities, circadian disruption, and emotional dysregulation. This association is observed across different populations, including children, perinatal women and elder people, and is linked to increased suicide risk. Physical activity and exercise improve both sleep quality and depressive symptoms and may help break this cycle. Conclusions: Sleep disturbances and depression are bidirectionally linked. Early identification and treatment of sleep problems, together with promotion of physical activity, may improve outcomes and support depression prevention.