Dose-response relationship of phototherapy for seasonal affective disorder: a meta-analysis

Objective: The therapeutic effect of phototherapy for seasonal affective di sorder (SAD) has been widely investigated. However, the antidepressant effe ct of various light intensities is inconclusive. The purpose of this study was to evaluate the dose-response relationship of phototherapy for SAD. Method: A meta-analytical methodology was applied to 39 studies of photothe rapy for SAD. The studies collected were screened for study quality by a th reats-to-validity method before inclusion. The fixed-effects-model analysis of variance procedures were used for data analysis. Results: The results indicated that different light intensities produced di fferent effects in reducing the typical symptoms, as measured by the Hamilt on Depression Rating Scale, of patients with SAD. However, no significant d ifferences in these effects were revealed between strong, medium and dim li ght in reducing the atypical symptoms of patients. Conclusion: These findings showed that light intensity varied positively wi th the antidepressant effect for typical but not for atypical symptoms of S AD, suggesting that light intensity tended to have different therapeutic ef fects on the typical and atypical symptoms of SAD.