A meta-analysis was conducted to evaluate the effectiveness of using light therapy with the treatment of Seasonal (SAD) and Non-Seasonal Major Depressive Disorder (MDD). Although there was a substantial amount of research supporting the effectiveness of light therapy for SAD, there was no conclusive evidence indicating what specific aspects of administration are needed for the most efficacious treatment. In addition, there was little empirical research examining the possible use of light treatment for MDD. In addition to overall effectiveness, specific aspects of the treatment were reviewed such as time of day, number of days, number of minutes, and intensity of treatment. Also, the efficacy of treating typical symptoms in MDD compared to treating atypical symptoms in SAD was examined. A total of 31 trials within 19 studies were included. Four trials examined MDD and 27 examined SAD. Results suggested that light treatment was an effective treatment for both SAD and MDD, but was more effective for treating SAD. Specifically light treatment given both in the morning and evening, for 240 minutes or longer, and at a medium light intensity creates the most effective treatment combination for SAD. MDD had only one combination of variation in treatment but results were similar to SAD, except all treatment was given in the AM. The analysis suggested that light therapy was effective for treating all depression symptoms but slightly more effective at treating typical depression symptoms than atypical symptoms. Overall, the findings are discussed in relevance to treatment and further research that is needed.
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