Seasonal affective disorder (SAD) is a mood disorder characterized by recurrent depressive episodes that occur and resolve with changes of season. Although recurrent spring-summer depressions have been documented and may be classified as SAD, the most common form of the disorder involves onset of depression in the late fall or early winter with remission in the spring or summer. Thus, winter pattern SAD is the focus of the majority of studies that have been conducted.
The only widely-used instrument to detect SAD is the Seasonal Pattern Assessment Questionnaire (SPAQ), a questionnaire that looks back in time and assesses the magnitude of seasonal change in sleep, social activity, mood, weight, appetite and energy. The SPAQ is a very simple, brief and useful screening questionnaire, but a careful clinical evaluation is still necessary to confirm the diagnosis.
Using the SPAQ questionnaire alone, the incidence of SAD is about 1-10% in North America and 1% in Asia. A more thorough evaluation places the incidence at 2-3% in Canada and 1% in the United States. For comparison, this is about the same incidence as manic-depressive disorder.
It has been a common belief that there is an increase in prevalence of SAD with increasing latitude (further north, with longer winters). However, more recent studies have shown that the latitude effect is not as robust as previously thought.
Prolonged periods of gloomy weather often affect our moods negatively. For those with SAD, this effect is more powerful and can significantly interfere with their lives.
Craving fatty foods and sweets is a common sign of SAD.
High-density negative air ionization may be an effective alternative or adjunct treatment to light therapy and medications.
For more than 15 years, patients have used light therapy for the treatment of SAD either individually or under the direction of a medical practitioner. The most commonly used and studied form of light therapy involves the use of a light box that administers bright light during a particular time of day, usually in the morning but sometimes in the evening. More recently developed but less studied forms of light therapy include dawn light simulation and the use of light visors. The antidepressant effects of light therapy are thought to be mediated through the eyes, not through skin exposure.
Combinations of the three components of light therapy (timing, intensity and duration) can affect the outcome of treatment. Long-term efficacy has not been established, and the intensity-response relationship, the optimal treatment schedule, and the long-term safety of light therapy have also not been clarified.
Although there as been controversy about the importance of timing, studies have confirmed that, on average, morning light therapy is superior to evening light exposure. The wavelength or type of light (incandescent, fluorescent) is not as important as intensity, but white light may be superior to narrow band wavelengths. Ultraviolet wavelengths are not necessary for the antidepressant response, and should be avoided because of long term toxicity.
Light intensity is usually expressed in "lux", a unit of luminance. As a reference, indoor lighting is usually less than 500 lux, outdoor light on a cloudy day ranges from 1,000 lux to 5,000 lux, and midday summer sunlight can reach 50,000 lux or higher. The usual dose of light therapy used in previous studies was 2,500 lux for at least one to two hours per day, but further research showed similar benefit with 30 minutes of 10,000 lux exposure. Since shorter periods of exposure are more convenient, the 10,000 lux fluorescent light box has become the clinical standard.
Commercial light devices are now widely available in medical supply stores or through mail order. A light device should meet government electrical safety standards, have a filter for the ultraviolet wavelengths and have been tested in reputable clinical trials. Patients must maintain proper distance and positioning to ensure the correct dose of light exposure. Because of the rapid response and relapse with light therapy, patients should become involved as active participants in determining their optimal dosing of light. For example, if patients respond to early morning light exposure, but the time is inconvenient for them, they can try shifting the exposure time to afternoon or early evening. Alternatively, they can try to reduce the duration of exposure to 15 minutes for maintenance.
Some response to light therapy generally occurs within two to four days, and measurable improvement is often seen in one week. Most patients experience rapid recurrence of symptoms after discontinuing light therapy. Longer trials have shown increasing improvement after two weeks, and further gains at three or four weeks.
The common side effects of light therapy reported by patients in clinical trials include eye strain or visual disturbances (19%-27%), headache (13%-21%), agitation or feeling "wired" (6%-13%), nausea (7%), sweating (7%) and sedation (6%-7%). These side effects are generally mild and subside with time or by reducing the dose of light. Extreme mood shifts have also been reported as uncommon but serious side effects of light therapy.
Light therapy should be administered under the guidance of an experienced and trained medical professional to properly diagnosed patients who have no psychotic disorder and who are not suicidal. Light therapy continues to be an investigational treatment, but with well-established benefits for users.
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