Seasonal affective disorder, or SAD, also known as winter depression is an affective (mood) disorder.

Most SAD sufferers experience normal mental health throughout most of the year, but experience depressive symptoms in the winter or summer.

SAD is rare in the tropics, but is measurably present at latitudes north of 30°N, or south of 30°S.


Seasonal mood variations are believed to be related mostly to light, not temperature. For this reason, SAD is prevalent even in mid-latitude places with mild winters, such as Seattle and Vancouver. People who live in the Arctic region are especially susceptible due to the effects of polar nights.

Prolonged periods of overcast weather can also exacerbate SAD.

SAD can be a serious disorder and may require hospitalisation. The symptoms of SAD mimic those of dysthymia or clinical depression. At times, patients may not feel depressed, but rather lack energy to get out of bed and do things.

Various aetiologies have been suggested. One possibility is that SAD is related to a lack of serotonin and that exposure to full-spectrum artificial light may improve the condition by stimulating serotonin production, although this has been disputed. Another theory is that melatonin produced in the pineal gland is the primary cause, since there are direct connections between the retina and the pineal gland. Some studies show that melatonin levels do not appear to differ between those with and without SAD. However, mice incapable of synthesizing melatonin appear to express "depression-like" behaviours and melatonin receptor ligands produce antidepressant-like effect in mice.

Although Dr. Rosenthal first called this disorder "winter blues", this term is more often used to describe a milder form of SAD experienced by a greater number during the winter. This "blue" feeling can usually be diminished by exercise and increased outdoor activity, particularly on sunny days (increased solar exposure).

Connections between human mood, energy levels, and the seasons are well-documented, even in healthy individuals. In high latitudes (50°N or S) it is particularly common for people to experience lower energy levels.


A number of treatments exist for SAD. These include light therapies, medication, ionized-air reception and cognitive therapy.

Treatments using light are the most common and, of these bright light therapies, tend to be the treatment of choice. The use of a therapeutic light box is the most effective, leading to an approximately 85 percent success rate. A specially designed light, many times brighter than normal office lighting, is placed near the sufferer. It should provide a dose of 10,000 lux. Many use it for 30-60 minutes daily. The sufferer should remain within sight of the light-box, with their eyes open and unshielded, only occasionally glancing at the light box. The best time to administer light therapy is still a matter of debate. Most patients use the light box in the morning, however discovering the best schedule on an individual basis is essential in reducing symptoms. In fact, some studies have shown dawn simulation to be more effective than bright lights in treating SAD. Light therapy may take several weeks to take full effect though some improvement should be noted within a week. It should be continued until natural daily light exposure becomes sufficient, usually during spring.

Another mode of treatment is prescription medication. SSRI (selective serotonin reuptake inhibitor) antidepressants have proven effective in treating SAD. Examples of these antidepressants are fluoxetine (Prozac), sertraline (Zoloft), or paroxetine (Paxil). Bupropion (Wellbutrin), an antidepressant of the aminoketone class, is also effective. Fluoxetine does not appear to be any more effective than light therapy in direct head-to-head trials.

Negative air ionisation, involving the release of charged particles into the sleep environment, has also been found effective.

Depending upon the patient, one treatment (ie. lightbox) may be used in conjunction with another therapy (ie. medication and/or therapy).

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