Review article
Bright light therapy for nonseasonal depression: Meta-analysis of clinical trials

https://doi.org/10.1016/j.jad.2016.03.016Get rights and content

Highlights

  • Bright light therapy seems efficacious in improving nonseasonal depression.

  • It is particularly efficacious as monotherapy and for 2-5 weeks׳ duration of exposure.

  • The exposure intensity; treatment duration and study design need to be standardized.

  • The efficacy of light therapy in perinatal depression needs to be further explored.

Abstract

Background

Bright light therapy (BLT) is a well-established treatment for seasonal depression. In the last two decades, the interest in BLT has expanded to involve other nonseasonal types of depression. The role of BLT for nonseasonal depression remains unsettled. In view of the growing number of studies in this area, this review aimed to assess the efficacy of BLT in nonseasonal depression.

Methods

We searched Pubmed; Scopus; PsychINFO; Evidence Based Medicine Guidelines and Cochrane Library until December 2015. The Standardized mean difference was calculated to assess the efficacy of BLT in nonseasonal depression. Data were subgrouped according to different study characteristics. Heterogeneity was assessed by examining the I2 index.

Results

Nine trials met the inclusion criteria. After employing the more conservative random-effects model, the overall model showed a significant reduction of depressive symptoms after BLT administration (SMD=−0.62, P<0.001, I2=37%). In particular, BLT appears to be efficacious when administered for 2-5 weeks (SMD=−0.78, P<0.001, I2=0%), and as monotherapy (SMD=−0.71, P<0.001, I2=18%). Studies of BLT for perinatal depression have found statistically insignificant improvement (SMD=−0.17, P>0.05, I2=44%).

Limitations

The overall heterogeneity of the included trials was moderate. The participants were not adequately blinded to the intervention. The sample size was small for certain subgroups. The long-term effect of BLT on depression was not explored.

Conclusions

BLT appears to be efficacious, particularly when administered for 2–5 weeks’ duration and as monotherapy. There is an obvious need to optimize the duration and intensity of exposure, the timing and the duration of treatment sessions.

Introduction

The description of light therapy as a treatment option was first mentioned in association with the syndrome of seasonal affective disorder/winter type (SAD) (Rosenthal et al., 1984). This syndrome is characterized by episodes of major depression which follow a seasonal pattern, mostly occurring in winter and fall with full remission during spring and summer seasons (Even et al., 2008). Since these seasonal changes in mood are mediated by alterations in melatonin, which is a central hormone secreted by the pineal gland in a circadian pattern and regulated by the light-dark cycle (day and night) and the seasonal cycle, the exposure to bright light was proposed as the treatment of choice (Lewy et al., 1980). Several mechanisms were suggested to explain how bright light therapy (BLT) may alleviate depressive symptoms. First, early animal studies showed that light is able to shift the circadian and seasonal rhythms (De Coursey, 1960, Pittendrigh, 1960), thus modulating the chronobiological cycle (Murray et al., 2005). Second, it is believed that extending the duration of daylight during the winter season will modulate these rhythms by regulating the master clock, the suprachiasmatic nucleus (SCN), resulting in an antidepressant effect (Rosenthal et al., 1984). Afterwards, these hypotheses were supplanted by the phase shift hypothesis which attributed depression in SAD patients to phase delay in circadian rhythms relative to the sleep/wake cycles, with a smaller subgroup of these patients becoming depressed due to a phase advance (Lewy et al., 1987). However, the exact mechanism of action of BLT in the treatment of depression remains unclear (Pail et al., 2011).

The interest in BLT has expanded beyond SAD; many clinical trials reported conflicting conclusions about whether BLT is effective as a treatment modality in nonseasonal depression (Even et al., 2008). Earlier meta-analyses of trials on the efficacy of BLT revealed that it is efficacious in the treatment of the seasonal type of depression (Golden et al., 2005, Martensson et al., 2015). However, its application in nonseasonal depression is less clear as recent reviews have refrained from meta-analytically pooling data, due to the heterogeneity of studies (Even et al., 2008, Martensson et al., 2015). Because new trials on the efficacy of BLT in nonseasonal depression have been recently published, we decided to conduct a meta-analysis in order to assess the clinical efficacy of such treatment in nonseasonal depression.

Section snippets

Literature search

This systematic review protocol was registered at Prospero International Prospective Register of Systematic Reviews (Registration ID= CRD42015032297). We have systematically searched the following online databases: Pubmed; Scopus; PsycINFO; Evidence Based Medicine (EBM) Guidelines; JAMA evidence and the Cochrane library. Several MeSH terms were used to identify relevant literature: bright light therapy OR phototherapy AND depression OR major depressive disorders OR nonseasonal depression AND

Description of the included studies

Of the 1840 studies identified during the initial stage of the literature search, 41 full-text articles were retrieved and evaluated based on the selection criteria. Nine trials met the inclusion criteria. Fig. 1 depicts the selection process of the included trials. Data were extracted and pooled from 9 clinical trials (Corral et al., 2007, Dauphinais et al., 2012, Goel et al., 2005, Kripke et al., 1992, Lam et al., 2015, Lieverse et al., 2011, Mackert et al., 1991, Martiny et al., 2005,

Main findings and implications

In this meta-analysis, we included 9 clinical trials with a total of 419 patients enrolled in the intervention and control arms. The result of the analysis revealed that BLT significantly improved depressive symptoms in patients with nonseasonal depression. The leave-one-out sensitivity analysis showed that the efficacy of BLT on depression is robust and consistent, irrespective of the individual effect of any trial. Our results are consistent with previous reviews; Tuunainen et al. (2004)

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