Bright light therapy for depression and excessive daytime sleepiness in Parkinson's disease: a systematic review and meta-analysis of randomized controlled trials with dose-response meta-regression
Abstract
Background: Non-motor symptoms, including depression and excessive daytime sleepiness (EDS), reduce quality of life in Parkinson's disease (PD). Pharmacological treatments may cause side-effects, highlighting the need for non-pharmacological approaches. We conducted an updated meta-analysis with linear and non-linear dose-response meta-regression to evaluate bright light therapy (BLT) on depression and EDS in PD.
Methods: PubMed, Scopus, and WOS were systematically searched through September 2025. Risk of bias was assessed using RoB-2 and NIH single-arm tools. Mean difference (MD) or standardized mean difference (SMD) with 95%confidence intervals (CI) were pooled using fixed-effects models. Linear and non-linear dose-response meta-regressions were performed.
Results: Eight studies were identified, six included in meta-analysis. For EDS, five studies (n = 159) showed no significant effect of BLT (MD =-1.14, 95%CI [-2.43, 0.15], p = 0.083, I2 = 0%), with no linear (p = 0.78) or non-linear (p = 0.97) dose-response relationship. For depression, five studies (n = 194) also showed no significant effect (SMD =-0.13, 95%CI [-0.41, 0.16], p = 0.38, I2 = 0%), without linear (p = 0.82) or non-linear (p = 0.85) associations. Sensitivity analyses were consistent.
Conclusion: BLT was not associated with significant improvement in depression or EDS in PD, and no dose-response relationship was identified. Given methodological limitations, BLT cannot currently be recommended for clinical…
How strong is the evidence?
Evidence Hub reads this as a meta-analysis, done in people. Its evidence level is 1 of 5 (Highest · pooled evidence). Pooled evidence from several studies sits at the top of the evidence pyramid. Reported size: 194 participants or records.
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