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The New "Blue Light" Intervention for Seasonal Affective Disorder (SAD)

Authors: Michael E. Thase, MDFaculty and Disclosures



What is the evidence for light therapy, specifically the newer "blue light" 470 nm therapy, for seasonal affective disorder (SAD)?

Laura Davies, MD

Response from  Michael E. Thase, MD

Michael E. Thase, MD 
Professor of Psychiatry, University of Pittsburgh Medical Center; Chief, Division of Adult Academic Psychiatry, Western Psychiatric Institute and Clinic, Pittsburgh, Pennsylvania


Between 15% and 25% of people with recurrent depressive disorder manifest a seasonal pattern whereby the risk of depression increases during the fall and winter and decreases during spring and summer. Rates of such a "winter depression" pattern tend to be higher in regions with less sun exposure and lower in sunny climates with longer days. For the past several decades, researchers have been studying whether artificially extending the photoperiod with bright light could exert therapeutic effect and, if so, whether this effect would be specific to patients with "winter depression." It is fairly clear now that bright light has significant therapeutic effects[1] and, for patients with "winter depression," the magnitude of these effects is comparable to that of standard antidepressants such as fluoxetine.[2] Bright light exposure also has some antidepressant effects for patients with nonseasonal depression, although the magnitude of the effects is smaller,[1] less predictable,[3] and may be less sustained.[4] Light therapy is generally well tolerated; insomnia is probably the most common side effect. Although uncommon, treatment-emergent hypomania and mania have been reported.

Standardized and relatively attractive desktop-sized light units are readily available through Internet vendors; prices range from $200 to $400. These units typically deliver 10,000 lux of brightness with full-spectrum light. A typical course of therapy involves 30 to 60 minutes of light exposure each morning throughout the period of risk (ie, September through April). The major drawback of light therapy is the time involved: many patients lack the organization and motivation to persist with such a long course of therapy.

As a result, investigators are studying alternatives that may affect the circadian systems that mediate response to bright full-spectrum light. Two promising options are dawn simulation and negative air ionization at high flow rate, which can be administered during the final hours of sleep.[5] Narrow-spectrum blue light (468-nm light at 607 microW/cm2, with a 27-nm half-peak bandwidth), administered via a light-emitting diode (LED), has been shown to suppress melatonin as does full-spectrum bright light. In one recent trial, narrow-spectrum blue light was shown to exert significant antidepressant effects.[6] However, as this form of light therapy also appears to require 45 minutes of daily morning administration, it is not clear whether it will offer any advantages over conventional light therapy.

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