The effect of single-component sleep restriction therapy on depressive symptoms: A systematic review and meta-analysis.

Sleep restriction therapy is a behavioural component within cognitive behavioural therapy for insomnia and is an effective standalone treatment for insomnia, but its effect on depressive symptoms remains unclear. This review aimed to synthesise and evaluate the impact of single-component sleep restriction therapy on depressive symptoms relative to a control intervention. We searched electronic databases and sleep-related journals for randomised controlled trials and uncontrolled clinical trials, published from 1 January 1986 until 19 August 2023, that delivered sleep restriction therapy to adults with insomnia. Random-effects meta-analysis of standardised mean differences and Cochrane risk of bias assessment were performed on randomised controlled trials, while uncontrolled clinical trials were discussed narratively. The meta-analysis was pre-registered on PROSPERO (ID: CRD42020191803). We identified seven randomised controlled trials (N = 1102) and two uncontrolled clinical trials (N = 22). Findings suggest that sleep restriction therapy is associated with a medium effect for improvement in depressive symptoms at post-treatment (N = 6, g = -0.45 [95% confidence interval = -0.70 to -0.21], p < 0.001) and a small effect at follow-up (N = 4, g = -0.31 [95% confidence interval = -0.45 to -0.16], p < 0.001). Five of the seven included randomised controlled trials were judged to have a high risk of bias. Standalone sleep restriction therapy appears to be efficacious for improving depressive symptoms at post-treatment and follow-up. However, conclusions are tentative due to the small number of trials and because none of the trials was performed in a population with clinically defined depression. Large-scale trials are needed to test the effect of sleep restriction therapy in patients experiencing depression and insomnia. Findings also highlight the need to improve the standardisation and reporting of sleep restriction therapy procedures, and to design studies with more rigorous control arms to reduce potential bias.