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.