As the days become longer more people begin to notice the impact that daylight has upon our bodies. Though most people know that light is essential to regulation of our internal biological clock, only some know that light also plays a role in the regulation of mood, and even fewer understand the biological process that explains the relationship between darkness and depression. For those with SAD, the critical variable is not the season, nor the climate, nor other situational factors such as changes in employment status. The depression is activated and deactivated by the amount of daylight.
Years ago, Dr. Norman Rosenthal at the National Institute for Mental Health found that some patients became very sluggish, irritable, and depressed as days grew shorter. They slept excessively, binged on carbohydrates, and withdrew from social activities. In essence, their depressed behavior replicated a mild form of primitive biological hibernation.
This type of mood change in response to the decreased exposure to daylight is known as Seasonal Affective Disorder (SAD). For those with SAD, the symptoms tend to come and go at about the same time each year. It is estimated that in North America six percent of the population has SAD. Three times as many may have a milder case of winter blues.
SAD is most common in Northern latitudes (which include Michigan) and among young adult women. The incidence of SAD in various regions of the world is directly related to each particular region's distance from the equator. That is, SAD is found with higher frequency in locations furthest from the tropics, where there are fewer hours of daylight.
Light entering our eyes through the retina transmits impulses along the optic nerve to the hypothalamus. This brain structure controls numerous activities including sexual urges, thirst and hunger, body temperature, aggression, and emotions such as pleasure and sadness. The hypothalamus transmits information about light to the pineal gland which regulates the production of melatonin which acts on the hypothalamus. Melatonin induces sleep, decreases mental agility and appears to depress mood. Absence of light results in increased melatonin secretion and SAD.
SAD can be effectively treated via various behavioral changes. Maintaining a regular sleep and wakefulness schedule even on weekends and getting regular exercise can combat some of the symptoms. In addition, use of a specially designed light box which mimics sunlight can also be very helpful. Light therapy has been used to treat SAD since the 1980's. These specially designed light boxes contain high intensity full-spectrum light bulbs placed behind a diffusing screen which filters out the glare and almost 100% of the UV rays.
The light emitted from a typical box at a comfortable distance is equivalent to a clear sunny spring morning. Exposure times of as little as 15 to 30 minutes a day are sufficient to halt melatonin production. Exposure in the morning is recommended for those who struggle to wake up during the winter months. Exposure in the evening is preferable for those who feel sleepy in the early evening.
Bright-light therapy relieves symptoms of SAD for about two thirds of people with SAD and has few side effects. Symptoms may improve within a few days of starting bright-light therapy or may take as long as three to four weeks. A study published in the American Journal of Psychiatry in 2006 found that: treatment with light therapy was just as effective as treatment with an anti-depressant; light therapy patients had more improvement after just one week; and patients had some unpleasant medication related side effects.
If you think that you may have SAD it is important that you consult a professional in order to get an accurate diagnosis. Light therapy will not help if your symptoms are not the result of SAD. Before starting light therapy it is important to rule out other diagnoses which would require other treatments, and to take precautions and evaluate contraindications for the use of a light box.
Light box treatment for seasonal affective disorder (SAD) has traditionally consisted of exposure to a white light source. Because light is the most important environmental stimulus for regulating circadian cycles and because blue light is far superior to white in shifting circadian rhythms, many have suggested that blue light would be the treatment of choice for Seasonal Depression. Though some research has found success in treating SAD with exposure to a lower wavelength light from the blue areas of the visible spectrum, there are differing opinions regarding blue light vs white light.
Because blue light is known to be more capable of causing damage to the retina, many researchers and clinicians recommend exercising caution, or possibly avoiding blue light for the treatment of SAD to minimize the risk of macular degeneration. Advocates of the use of blue light for the treatment of SAD note that any light at a high enough intensity is dangerous and that any potential risk is related to how long you're exposed each time you use the light box. They argue that in assessing the risk of exposure to 10,000 lux white light versus blue light the need for a shorter duration of exposure with blue light may offset the absolute risk that is greater than exposure with while light.
For many individuals, convenience and cost may influence the decision about which technology to employ. In general, the white light boxes cost more and are physically larger, whereas the blue light boxes are less costly and are more portable. However, because the white light boxes are larger, they can be used at a more comfortable distance.
Regardless of the technology, the recommended intensity of the light for the treatment of SAD is 10,000 lux. Boxes which emit less than 10,000 lux must be used for a duration that is inversely proportional to their intensity; a 2500 lux box (1/4 intensity) must be used 4 times as long as a 10,000 lux box.
The Center for Environmental Therapeutics (CET) summarizes their recommendations for choosing a light box for treatment of SAD:
- Any light box you buy should have been tested successfully in peer-reviewed clinical trials.
- The box should provide 10,000 lux of illumination at a comfortable sitting distance.
- Fluorescent lamps should have a smooth diffusing screen that filters out ultraviolet (UV) rays. UV rays are harmful to the eyes and skin.
- The lamps should give off white light rather than colored light. "Full spectrum" lamps and blue (or bluish) lamps provide no known therapeutic advantage.
- The light should be projected downward toward the eyes at an angle to minimize aversive visual glare.
- Smaller is not better: When using a compact light box, even small head movements will take the eyes out of the therapeutic range of the light.
There are approximately a dozen manufacturers of light boxes for the treatment of SAD. Most have an internet presence and offer a 30 day trial and money back guarantee.