Light Therapy for Depression, and Other Treatment of Seasonal Affective Disorder

SBU’s Conclusions

• The value of therapy with a light box for seasonal affective disorder (SAD or seasonal depression) can be neither confirmed nor dismissed. Thus, although a number of studies have been published since SBU released its “Treatment of Depression” report in 2004, the therapy should still be regarded as experimental. There is no significant difference between placebo and light therapy with regard to the number of patients who improve by at least 50%. The results are contradictory when it comes to the number of patients who experience remission. SBU’s meta-analysis of studies that use light boxes shows that the therapy reduces the severity of depression on a rating scale somewhat more than placebo during the first few weeks but that the effect is temporary (Evidence Grade: Insufficient Scientific Evidence).
• The evidence is insufficient to determine the effect of light therapy, whether as monotherapy or as an adjunct to antidepressants, on non-seasonal depression.
• Although treatment in light therapy rooms is well established in Sweden, no satisfactory, controlled studies have been published on the subject. Thus, there is a great need to conduct such studies with enough participants to draw reliable conclusions. Approximately 100 participants are required to establish whether the therapy is moderately more effective than placebo. The studies should also take health economic aspects into consideration.

Fact Box 1 Study Quality and Relevance, Evidence Grade
Study quality and relevance refers to the scientific quality of a particular study and its ability to reliably address a specific question.
Evidence Grade refers to the total scientific evidence for a conclusion, ie, how many high-quality studies support it.

Evidence Grade 1 – Strong Scientific Evidence
A conclusion assigned Evidence Grade 1 is supported by a good systematic literature overview with a meta-analysis or at least two studies with high quality and relevance among the total scientific evidence. If some studies are at variance with the conclusion, the Evidence Grade may be lower.

Evidence Grade 2 – Moderately Strong Scientific Evidence
A conclusion assigned Evidence Grade 2 is supported by a systematic literature overview with a meta-analysis that fails to meet the requirements for a good systematic overview in some respect or at least one study with high quality and relevance and two studies with medium quality and relevance among the total scientific evidence. If some studies are at variance with the conclusion, the Evidence Grade may be lower.

Evidence Grade 3 – Limited Scientific Evidence
A conclusion assigned Evidence Grade 3 is supported by a systematic literature overview with a meta-analysis that fails to meet the requirements for a good systematic overview in several respects or at least two studies with medium quality and relevance among the total scientific evidence. If some studies are at variance with the conclusion, the scientific evidence may be regarded as insufficient or contradictory.

Insufficient Scientific Evidence
If no studies meet the quality and relevance criteria, the scientific evidence is rated as insufficient to draw any conclusions.

Contradictory Scientific Evidence
If different studies are characterised by equal quality and relevance but generate conflicting results, the scientific evidence is rated as contradictory and no conclusions are drawn.