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Summary of Research on Seasonal Affective Disorder (SAD)

Originally published by the Lighting Design Lab

There is a great deal of mis-, and incomplete information about the effect of light on the human body. The past twenty years has seen considerable research on the effects of light on human behavior. The lack of accurate information about verifiable scientific research has led to the following problem areas: lighting products that have little effect other than as placebos are sold; consumers often spend more money than necessary for lighting solutions; and ineffective treatments are used for treating real problems. This handout is far from a complete reference of all the research on circadian rhythm disorders, but tries to touch on the highlights of research over the past dozen years, or so.

In the late 1970's Dr. Alfred Lewy and others from the National Institutes of Health began investigating the bio-chemical nature of depression. Interviews with thousands of patients showed some intriguing differences, related to the timing and nature of symptoms. For the majority of patients, clinical depression means bouts of insomnia, lack of interest in food, rejection of anything pleasurable, occurring on an unpredictable cycle. However, about 5% - 10% of patients have almost opposite symptoms. Generally beginning in late autumn, these patients began a pattern of overeating, and sleeping many extra hours as a means to cope with ongoing, debilitating depression. In mid-spring, the depression would lift, and behavior would generally return to normal, until the following fall, when the cycle began again. Several research studies were done to isolate the variables that might lead to these seasonal cycles of depression, and resulted in the theory that the depression was somehow related to the variation of light with the change in seasons.

But there was a problem with that theory - almost 75 years of research by the medical and lighting professions showed that human beings did not react to light like other mammals. Prior to the research by Lewy, and others, no research had shown that light affected biological processes in humans through the eye. Considerable research had shown the effect of light on humans via the skin, with the production of vitamin D, but the research on the effect of light through the eye had drawn a blank. Then, the research team made an interesting discovery... all previous research had been done using light levels typical of indoor lighting. Experiments were devised to see if higher light levels, similar to those found outdoors, had any effect on human biological response. Carefully controlled research showed that at around 1500 lux (approx. 150 footcandles) interesting things began to happen. Above 1500 lux, light begins to have an effect on respiration, blood pressure, body temperature, the internal clock, and the regulation of production of a chemical called melatonin. Light levels below this have no effect on any of these functions, no matter what type of light it is.

More research was done, exposing patients to light levels above 1500 lux for different periods. Many of the patients with seasonal cycles of depression showed improvement from light therapy, if the treatments were received early in the day. Treatments later in the day, in the afternoon or evening, showed no change, or made symptoms worse. Various schedules were tried, with evaluation of efficacy of the treatments. The greatest effectiveness was found in a treatment pattern of >2500 lux in the patient's field of vision for 1/2 hour every day, before 10 am. After about two weeks, the sessions are reduced to 15 minutes every day, then every other day. Effectiveness of treatment for patients with SAD in clinical settings is very high.

In the years since the initial studies on SAD, much new information has been uncovered. The optic nerve, which carries light to the rear of the brain for visual processing, branches off into an area of the hypothalmus called the superchiasmatic nucleus. The light that goes into this area makes changes in activity all over the body. High levels of light in early morning regulate production cycles of a chemical called melatonin later at night, in the dark. Imbalances in melatonin can lead to problems with other chemicals that may lead to depression. Most people do not have problems with melatonin production regulation, and there is no research that suggests that treatment with light for non-depressives will lead to any therapeutic benefits for the public at large.

In the early 1990's hundreds of thousands of people throughout North America participated in a medical survey that included questions about SAD. In this survey, almost 20% of the general public said they had some symptoms of seasonally related depression. When these answers were mapped out, a strikingly clear trend emerged. In the southernmost regions, Florida to Arizona, only a small percentage of the general population had symptoms (< 5%.), but when looking at places farther north, the numbers climbed significantly. By the latitudes of cities like Seattle, WA, the percentages of people claiming SAD symptoms climbed to >30%.

New research has looked at the effect of types of light sources on effectiveness of treatment. Studies compared incandescent, fluorescent, and high intensity discharge light sources, including products marketed as "full-spectrum". There was almost no variation in the effectiveness of treatment by type of light source. The light sources that were richer in blue-green frequencies were slightly more efficacious, but not significantly. These sources include fluorescent sources, metal halide and mercury vapor. No advantage of any sort was shown for the products marketed as "full-spectrum" sources. Fluorescent light has generally been chosen for treatment of SAD for 3 reasons: significant amounts of light can be generated for relatively few watts (meaning cheap); and relatively little heat is produced for the amount of light given off (meaning cool); fluorescent lighting equipment is relatively inexpensive and long lasting (again meaning cheap). Sitting next to 2500 lux in your field of view from an incandescent source would be like putting your face in an oven, and would require hundreds of watts of power. Using mercury vapor or other high intensity discharge sources would use little energy, but would be painfully bright, buzz and potentially expose you to high ultraviolet levels.

The biochemical mechanism for SAD is very closely related to jet lag and the problems of shift workers. Over half of the serious industrial accidents happen between midnight and 6 AM. The roll call of environmental disasters in that time frame is chilling - Three Mile Island, and Chernobyl nuclear accidents, Union Carbide's Bhopal chemical spill, Exxon Valdez oil spill. Workers on the night shift have significantly higher rates of heart disease and diseases of the digestive system. Pilot programs in businesses have been instituted to address the problems of night shift workers, travelers with jet lag and control room operators, based on the results of SAD research.

Treatment of Seasonal Affective Disorder should begin with a trip to a physician or therapist familiar with diagnosis and treatment of clinical depression. SAD should not be self-diagnosed, as the symptoms could be confused with a variety of other syndromes, ranging from diabetes to high blood pressure. SAD is NOT a variation on the sadness every human being encounters from time to time. Clinical depression is a cruelly debilitating disease with bio-chemical causes that can hamper living, and can be life-threatening in some individuals. If you suffer from bouts of depression, seasonal or otherwise, consult a physician and mental health professional, NOT A LIGHTING SALES PERSON.

The basic treatment for SAD consists of exposure to light levels similar to outdoors for about one-half hour every morning, preferably before 10 am (if you are on a typical 8 to 5 schedule). You can get these light levels by going outside and taking a walk, sitting within 2.5 feet of a 4-lamp fluorescent light fixture, or purchasing a light-box manufactured for this purpose. Current evidence shows no significant differences in the effectiveness of the three treatments. The effectiveness of any therapy depends upon how comfortable you are with the method of treatment. Believers in physical therapy and endorphins will benefit from the walking, while those with an abiding faith in technology will prefer high-tech light boxes. Decide what treatment route you would feel most comfortable with, but keep in mind what biochemical chain is delivering the benefits. It is the high levels of morning light suppressing melatonin production at night that is helping you, not the effects of some magic lighting products.

If your therapist recommends light therapy for you, do not stare into any light source, whether it is a light bulb, or the sun. Staring into a light source will not help SAD, it will only give you a headache. Simply keep the bright light in your field of vision while you engage in a normal activity - reading, watching television, hobbies, eating, etc. You might want to periodically look closer to the source, to ensure you are getting enough light. But anyone who tells you to look directly into a bright light source is causing you to temporarily injure your vision.

Here are research reports from some of the pioneers in exploration of Seasonal Affective Disorder:

  1. Lewy AJ, Wehr TA, Goodwin FK et al. Light suppresses melatonin secretion in humans. Science 1980: 210: 1267-1269.
  2. Lewy AJ, Kern HA, Rosenthal NE. et al. Bright artificial light treatment of a manic-depressive patient with a seasonal mood cycle. American Journal of Psychiatry 1982, 139: 1496-1498.
  3. Garvey MJ, Wesner R, Godes M. Comparison of seasonal and nonseasonal affective disorders. American Journal of Psychiatry 1988, 145: 100-102.
  4. Brainard GC, Lewy AJ, Menaker M, et al. Effect of light wavelength on suppression of nocturnal plasma melatonin in normal volunteers. Annal of the New York Academy of Sciences 1985, 455:376-378
  5. Lewy AJ, Sack RL, Singer CM. Treating phase type chronobiological sleep and mood disorders using appropriately timed bright artificial light. Psychopharmacological Bulletin 1985, 21:368-372
  6. Boyce P, Kennaway DJ. Effects of light on melatonin production. Biological Psychiatry 1987, 22:473-478

Copies of these and related articles may be available from your local library, a university library or medical reference library.