A study commissioned by the American Psychiatric Association and led by a psychiatrist at the University of North Carolina at Chapel Hill School of Medicine has found that light therapy effectively treats mood disorders, including seasonal affective disorder (SAD) and other depressive disorders.
A report of the study, which appeared April 1 in the American Journal of Psychiatry, also finds that the effects of light therapy, also known as phototherapy, are comparable to those found in many clinical studies of antidepressant drug therapy for these disorders.
The findings were based on a meta-analysis, a systematic statistical review of 20 randomized, controlled studies previously reported in the scientific literature. These represented only 12 percent of 173 published studies that the authors had originally considered for review.
"We found that many reports on the efficacy of light therapy are not based on rigorous study designs. This has fueled the controversy in the field as to whether or not light therapy is effective for SAD or for non-seasonal forms of mood disorders," said lead author Dr. Robert Golden, professor and chairman of psychiatry at UNC and vice dean of the medical school.
"But when you throw out all the studies that are methodologically flawed and then conduct a meta-analysis of those that are well-designed, you find that light therapy is an effective treatment not only for SAD but also for depression."
The use of bright artificial light for people with SAD, a recurring depression that develops in the fall or winter and spontaneously disappears during spring or summer, was first described in the Archives of General Psychiatry in 1984. Since then, the treatment has been tried in clinical and research programs for non-seasonal mood disorders, Alzheimer's disease, jet lag, insomnia, eating disorders and other behavioral problems.
A more recent light therapy approach is "dawn simulation," which attempts to simulate an earlier dawn through exposure to artificial light. This follows the theory that SAD is triggered by the reduced period of bright daylight during winter.
The method attempts to recreate the increased intensity of sunlight that occurs in nature in the summer when the sun rises earlier in the day. "The logic here is that it might put people with seasonal affective disorder into remission," Golden said.
Still, the exact mechanisms by which light therapy works remain unclear, the researchers said.
The studies selected by the authors for inclusion in their meta-analysis were grouped into four categories: bright light for SAD, bright light for non-seasonal depression, dawn simulation for SAD and bright light as an adjunct therapy combined with conventional antidepressants for non-seasonal affective disorder.
These study groups were limited to adults ages 18 to 65 years who met a criterion-based mood disorder diagnosis.
The meta-analysis demonstrated statistically significant treatment effects for SAD, dawn simulation for SAD and bright light treatment of non-seasonal depression, the report said.
"The effect size of the light therapy intervention in our meta-analysis was comparable to what has been described in the clinical literature for conventional medications to treat depression," Golden said. "The findings are as strong or as striking."
More research is needed on the safety of light therapy, particularly among children and the elderly, Golden said. The study did not look at safety or adverse effects, as very few reports contain controlled, or comparison, data on side effects or toxicity, the authors reported.
In addition, they added, the responses of children, adolescents and the elderly to light therapy may differ, compared to non-geriatric adults. For example, at each end of the age spectrum, the requirements for light therapy dosing might differ. Also, children and adolescents may need lower doses than the elderly. "And if eye problems such as cataracts are more prevalent among the elderly, might light therapy aggravate the problem, even slightly?", Golden added.
As to efficacy of light therapy for SAD and other non-seasonal depressive mood disorders, Golden said this study largely answers the question: The treatment is effective.
"The study also points to the importance of conducting systematic literature reviews in areas of controversy using well-defined standards of what constitutes good study design, and to follow this up with meta-analyses so that the data can speak for themselves. "And when you can separate the wheat from the chaff, the findings are much more valid."