The effects of bright light therapy on depression, sleep and circadian rhythm in patients with Parkinson's disease and a depressive disorder: results of a double-blind randomized controlled trial

Abstract

Objective: The aim of this study was to assess the efficacy of Bright Light Therapy (BLT) in reducing depressive symptoms in patients with Parkinson's disease (PD) and major depressive disorder (MDD), compared with exposure to a control light. Background: A disturbed circadian rhythm may be a causal factor in the development of MDD and insomnia in PD patients. BLT supports the circadian rhythm and might therefore be a new treatment option for MDD and insomnia in PD. Methods: In this double‐blind controlled trial, patients with idiopathic PD and MDD were randomized to the intervention or control group. The intervention group was treated with BLT (±10,000 Lux), the control group with control light (±200 Lux). Participants were treated at home with 30 minutes of light therapy at fixed times in the morning and evening. The treatment period lasted three months, after which the participants entered a naturalistic follow‐up period of six months. Assessments were repeated halfway and at the end of the treatment phase, and one, three and six months post‐treatment. The primary outcome of the study was depression, as measured with the Hamilton Depression Rating Scale (HDRS). Secondary outcomes were ancillary depression measures, objective and subjective sleep parameters, and salivary melatonin and cortisol concentrations as markers of the circadian rhythm. Data were analyzed using a linear mixed model analysis. Results: Of the 389 patients assessed for eligibility, 306 were excluded, resulting in sample size of 83. Mean age was 64.4±9.2 SD years, and 44% of the participants were female. During treatment, HDRS scores decreased in both groups, without a significant between‐group difference at the end of treatment. Subjective sleep quality improved in both groups, with a larger improvement in the intervention group (B (SE) = 0.36 (0.18), p = 0.05). The total salivary cortisol secretion decreased in the intervention group, while it increased in the control group, resulting in a significant between group‐difference at the end of the intervention (B(SE) =‐8.11 (3.93), p = 0.04). Conclusions: BLT was not more effective in reducing depressive symptoms than exposure to a control light. Both the intervention and the control group showed an improvement of mood and subjective sleep during treatment. BLT was more effective in improving subjective sleep quality than control light, possibly through a BLT‐induced decrease in cortisol levels.