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April 2001; Volume 4; 40-43
By Barak Gaster, MD
"In the dark of winter let there be light." so reads the menu of a trendy café in Helsinki, where Danish pastry and coffee may run $7, but the use of the light box at the table is free.
Seasonal affective disorder (SAD), the official name for depression occurring at the onset of winter and resolving with spring, affects an estimated 10 million Americans.1 Thousands of people who suffer from SAD consider artificial light therapy to be therapeutic, and dozens of companies market light-therapy devices.
The first therapeutic light box was built in the early 1980s by researchers at the National Institutes of Mental Health, who reported the dramatic remission of seasonal depression in a 63-year-old engineer. In the 20 years since, a large amount of data have accumulated supporting the safety and efficacy of light therapy for the treatment of SAD.
Mechanism of Action
The precise pathophysiology of SAD is unknown. Since 1980, it has been known that exposing the retina to bright light suppresses melatonin production by the pineal gland. In 1982, when light therapy was shown to be effective for the treatment of SAD, the obvious explanation was that it caused phase shifting of the circadian rhythm of melatonin production in the brain.
Since then, further research has shown that light’s effects on melatonin can only partly explain the efficacy of light therapy.2 Other possible mechanisms of action include bright light’s effects on 1) serotonin activity, 2) retinal sensitivity, or 3) cortisol regulation.3 Studies suggest that retinal stimulation is required for light therapy to work.
There have been more than 60 randomized, controlled trials of light therapy for SAD. Almost all have shown a positive effect.
The placebo effect is a serious problem in light therapy research, because light therapy is almost impossible to test in a truly blinded fashion. In addition, almost all the patients who have participated in studies of light therapy have been recruited with media advertisements, such that almost all of those who enroll in trials begin with a strong belief that light therapy works. The two best studies have attempted to address this difficult research problem.4,5
In the first of these studies, Eastman randomized 96 patients to either morning light, evening light, or placebo.5 Patients in the treatment groups received bright light (6,000 lux) for 1.5 hours/d, while the placebo group was exposed to a sham device. Patients in this placebo group were told that the sham device would expose them to a high concentration of negative ions, approximating the high concentration of negative ions in summer air. To increase patients’ belief that sitting in front of the device would be beneficial, the device made a humming noise. Patient questionnaires at entry into the study and just prior to treatment suggested that most patients were convinced that negative ion therapy and bright light had an equal chance of working.
The proportion of patients who had more than a 50% reduction in their depression scores at the end of four weeks was significantly greater in the treatment groups than in the placebo group (61% morning light, 50% evening light, 32% placebo, P < 0.05 for the comparison between treatment groups and placebo).
In the second of these studies, Terman randomized 158 patients to bright light, a high-intensity negative ion generator, or a low-intensity negative ion generator.4 The ion generators in this study in fact did generate negative ions. Patients exposed to light therapy had a 30% higher response rate than those receiving low-intensity negative ions, while the high-intensity ion group had an intermediate response.
Finally, additional research has been summarized in two meta-analyses. One reported on the results of 14 trials (total of 322 patients) which found that patients who received an average of 2,500 lux daily had significant improvement in their depression scores compared to patients who were exposed to dim light only.6 Another more recent meta-analysis found a dose-response relationship between the intensity of light therapy and its antidepressant effect.7
Light therapy is generally well tolerated. About 15% of patients experience mild eye strain or headache, which can be eliminated by having patients sit either further from the light or for a shorter time each day.8 It is not known whether this reduces effectiveness. Similar rates were reported for light intensities up to 10,000 lux.9
There are no known contraindications to light therapy, and no evidence that light therapy is associated with ocular damage.8,10 Patients with eye disease or those who are at high risk for eye disease, such as those with macular degeneration, glaucoma, cataracts, or diabetes, should consult with an ophthalmologist prior to starting light therapy.8 No harmful light/drug interactions have been reported.11
Light Intensity and Duration
Most studies of light therapy in the 1990s exposed patients to 2,500 lux lights for two hours/d. More recently, researchers have realized that patient compliance and acceptability are higher and efficacy seems to be about the same with a 10,000 lux light used for 30 minutes/d.
The average room lighting in a typical household ranges from 100 to 200 lux, and in the workplace it averages 200 to 400 lux. Outside light from midday sun ranges from 1,000 to 50,000 lux depending on weather conditions, distance from the equator, and time of year.
Light boxes should be placed on a table or counter just above eye level to allow a patient’s head to be within 12-18 inches of the light. Patients can work or eat while sitting under the light as long as their eyes are not shut. Patients need not look into the box, but should simply regard it as they would overhead room lighting. Sunscreen is not necessary with appropriate UV filtering.
Morning therapy generally is more effective than evening therapy.8 Patients who do not respond to morning therapy should try evening therapy, since some patients respond to one but not the other. Light therapy works best if patients are encouraged to become active participants in their care, experimenting to establish their own personal, optimal schedule.
Patients should notice a response to light therapy within 4-14 days.7,8 This generally is faster response than is seen with selective serotonin reuptake inhibitors.12
Patients should continue maintenance therapy until the end of the season, since depressive symptoms often recur if light therapy is withdrawn too soon.7 After two to four weeks, the duration of daily therapy sessions usually can be reduced by 50% without loss of efficacy.8
Light Boxes and Other Devices
Light boxes have emerged as the gold standard for light therapy. Good light boxes have filters to screen out UV light. UV light does not seem to contribute to the efficacy of light therapy, and it can cause significant damage to the eyes and skin.13
Other types of devices, such as head-mounted visors or dawn simulators, have been less well-studied.7 Standard sun lamps should not be used for light therapy as they deliver a high content of UV light. Tanning salons are unlikely to be effective, since the tanner’s eyes are covered during these sessions.
There are no data to suggest that more expensive full-spectrum lights, which provide more uniform light across the visual spectrum, offer any advantage over standard fluorescent bulbs.13,14 This idea, and the vigorous commercial marketing that goes along with it, stems from the specialized full spectrum light that was used in the first study of light therapy. Then, researchers believed that they should try to mimic the sun’s rays as closely as possible. Researchers have since realized that standard white fluorescent lights work equally well.
Light boxes are readily available on the Internet and generally cost between $200 and $600. (See Table 1.) Few insurers will reimburse their cost. The Society for Light Treatment and Biological Rhythms maintains a list of such companies on their web site (www.sltbr.org).
|Table 1: Light therapy devices|
|Device||Brightness||UV light source||Price|
|SunRay I||10,000 lux at 18.5"||non-UV||$319|
|WinterBright||10,000 lux||UV shielded||$299|
|SunnyDays Desk Lamp||10,000 lux at 10"||non-UV||$219|
|NorthStar 10,000||10,000 lux at 26"||non-UV||$199|
|Source: On-line mail-order firms|
Light therapy appears to be safe and effective for the treatment of SAD and is the treatment of choice for this common condition.15 Given the problems in achieving adequate placebo controls in light therapy research, however, it is difficult to assess what portion of the treatment response to light therapy derives from the placebo effect.
Starting in late fall, patients who suffer from winter SAD should sit in front of a UV-filtered standard fluorescent light box that is rated at 10,000 lux for 30 minutes each morning. After two to four weeks, patients can experiment by cutting back to 15 minutes each morning, continuing maintenance therapy until early spring.
Dr. Gaster is Assistant Professor, Department of Medicine at the University of Washington in Seattle.
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2. Terman JS, et al. Circadian time of morning light administration and therapeutic response in winter depression. Arch Gen Psychiatry 2001;58:69-75.
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5. Eastman CI, et al. Bright light treatment of winter depression: A placebo-controlled trial. Arch Gen Psychiatry 1998;55:883-889.
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10. Gallin PF, et al. Ophthalmologic examination of patients with seasonal affective disorder, before and after bright light therapy. Am J Ophthalmol 1995;119:202-210.
11. Schwartz PJ, et al. Winter seasonal affective disorder: A follow-up study of the first 59 patients of the National Institute of Mental Health Seasonal Studies Program. Am J Psychiatry 1996;153:1028-1036.
12. Ruhrmann S, et al. Effects of fluoxetine versus bright light in the treatment of seasonal affective disorder. Psychol Med 1998;28:923-933.
13. Lee TM, et al. Spectral properties of phototherapy for seasonal affective disorder: A meta-analysis. Acta Psychiatr Scand 1997;96:117-121.
14. Bielski RJ, et al. Phototherapy with broad spectrum white fluorescent light: A comparative study. Psychiatry Res 1992;43:167-175.
15. Depression in Primary Care. Rockville, MD: U.S. Department of Health and Human Services, Agency for Health Care Policy and Research;1993. AHCPR publication 93-0551.