Seasonal Affective Disorder (SAD)
Seasonal affective disorder (SAD), also known as winter depression, is a mood disorder. Most SAD sufferers experience normal mental health throughout most of the year, but experience depressive symptoms in the winter. When the depressive symptoms occur in summer rather than winter, the condition is often referred to as reverse seasonal affective disorder (RSAD) and can include heightened anxiety.
Seasonal mood variations are believed to be related to light. An argument for this view is the effectiveness of bright light therapy. SAD is measurably present at latitudes in the Arctic region, such as Finland (64º 00´N) where the rate of SAD is 9.5% Cloud cover may contribute to the negative effects of SAD.
SAD can be a serious disorder and may require hospitalization. There is also potential risk of suicide in some patients experiencing SAD. One study reports 6-35% of sufferers required hospitalization during one period of illness. The symptoms of SAD mimic those of dysthymia or clinical depression. At times, patients may not feel depressed, but rather lack energy to perform everyday activities. Norman Rosenthal, a pioneer in SAD research, has estimated that the prevalence of SAD in the adult United States population is between about 1.5 percent in Florida and about 9 percent in the northern US.
Various etiologies have been suggested. One possibility is that SAD is related to a lack of serotonin, and serotonin polymorphisms could play a role in SAD, although this has been disputed. Another theory is that the cause may be related to melatonin which is produced in dim light and darkness by the pineal gland, since there are direct connections, via the retinohypothalamic tract and the suprachiasmatic nucleus, between the retina and the pineal gland. Mice incapable of synthesizing melatonin appear to express "depression-like" behaviors, melatonin receptor ligands produce an antidepressant-like effect.
Subsyndromal Seasonal Affective Disorder is a milder form of SAD experienced by an estimated 14.3% vs. 6.4% of the U.S. population. The blue feeling experienced by both SAD and SSAD sufferers can usually be dampened or extinguished by exercise and increased outdoor activity, particularly on sunny days, resulting in increased solar exposure. Connections between human mood, as well as energy levels, and the seasons are well-documented, even in healthy individuals.
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