Bright white light therapy in depression: A critical review of the evidence

Light therapy is an accepted treatment option, at least for seasonal affective disorder (SAD). Our aim was to critically evaluate treatment effects of bright white light (BWL) on the depressive symptoms in both SAD and non-seasonal depression.

The systematic review was performed according to the PRISMA guidelines. PubMed, Embase, and PsycINFO were searched (December 1974 through June 2014) for randomized controlled trials published in peer-reviewed journals. Study quality was assessed with a checklist developed by the Swedish Council on Technology Assessment in Health Care. Only studies with high or medium quality were used in the meta-analyses.

Eight studies of SAD and two studies of non-seasonal depression met inclusion and quality criteria. Effects on SAD were estimated in two meta-analyses. In the first, week by week, BWL reached statistical significance only at two and three weeks of treatment (Standardized Mean Difference, SMD: -0.50 (-CI 0.94, -0.05); -0.31 (-0.59, -0.03) respectively). The second meta-analysis, of endpoint data only, showed a SMD of -0.54 (CI: -0.95, -0.13), which indicates an advantage for BWL. No meta-analysis was performed for non-seasonal depression due to heterogeneity between studies.

This analysis is restricted to short-term effects of BWL measured as mean changes in scores derived from SIGH-SAD, SIGH-SAD self-report, or HDRS rating scales.

Most studies of BWL have considerable methodological problems, and the results of published meta-analyses are highly dependent on the study selection. Even though quality criteria are introduced in the selection procedures of studies, when the results are carefully scrutinized, the evidence is not unequivocal.