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

May 30, 2026Neurodegenerative disease management

Bright light therapy for depression and daytime sleepiness in Parkinson's disease: a review and analysis of controlled trials examining different doses

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Abstract

Bright light therapy (BLT) showed no significant effects on depression or excessive daytime sleepiness in Parkinson's disease.

Five studies involving 159 participants indicated no significant effect of BLT on excessive daytime sleepiness, with a mean difference of -1.14.
Five studies with 194 participants also found no significant effect of BLT on depression, resulting in a standardized mean difference of -0.13.
No linear or non-linear dose-response relationships were identified for either excessive daytime sleepiness or depression.
Sensitivity analyses confirmed the consistency of findings.
Due to methodological limitations, BLT cannot currently be recommended for clinical use.

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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 ( = 159) showed no significant effect of BLT (MD =-1.14, 95%CI [-2.43, 0.15], = 0.083, I = 0%), with no linear ( = 0.78) or non-linear ( = 0.97) dose-response relationship. For depression, five studies ( = 194) also showed no significant effect (SMD =-0.13, 95%CI [-0.41, 0.16], = 0.38, I = 0%), without linear ( = 0.82) or non-linear ( = 0.85) associations. Sensitivity analyses were consistent. n p p p n p p p2 2

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 use. Future standardized dose-finding trials stratified by disease stage and retinal/ipRGC integrity are needed.

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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

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