Introduction Sleep restriction therapy (SRT) is a behavioural component within cognitive behavioural therapy for insomnia (CBT-I) and is an effective standalone treatment, but its effect on depressive symptoms remains unclear. This review aimed to synthesize and evaluate the impact of single-component SRT on depressive symptoms and negative affect using meta-analysis and narrative synthesis.

Methods We searched electronic databases and sleep relevant journals for randomised controlled trials (RCTs) and uncontrolled clinical trials (UCTs) published between 1986 and March 2023, which investigated SRT in adults with insomnia. Meta-analysis was conducted on RCTs, while UCTs were synthesised and discussed narratively. The primary outcome was depressive symptoms at post-treatment. This study was pre-registered in PROSPERO, CRD42020191803.

Results We identified seven RCTs (N = 1102) and four UCTs (N = 49). Findings suggest that SRT is associated with a medium effect size for improvement in depressive symptoms at post-treatment (Nc = 6; Np = 847, g = -0.45 [95% CI = -0.68 to -0.22], p = <0.0001) and a small effect size at follow up (Nc = 4; Np = 735, g = -0.31 [95% CI = -0.45 to -0.16], p = <0.0001). Five of the seven included RCTs were judged to have high risk of bias. Heterogeneity among the studies was moderate at post-treatment (I2 = 45.5% [95% CI = 0 to 78], p = 0.11) and small at follow-up (I2 = 0% [95% CI = 0 to 84.7], p = 0.83).

Discussion Standalone SRT appears to improve depressive symptoms at post-treatment and follow-up. However, conclusions are tentative due to the small number of trials and because no studies were performed in patients with clinically diagnosed depression Findings also highlight the need to improve the reporting and standardisation of SRT.