Seasonal Affective Disorder, or SAD, is a type of recurrent major depressive disorder in which episodes of depression occur during the same season each year. This condition is sometimes called the "winter blues," because the most common seasonal pattern is for depressive episodes to appear in the fall or winter and remit in the spring. Less commonly, SAD occurs as a summer depression, typically beginning in the late spring or early summer and remitting in the fall. SAD may be related to changes in the amount of daylight a person receives.
To be diagnosed with SAD, an individual must meet criteria for major depression coinciding with specific seasons for at least two years. The individual must experience seasonal depressions much more frequently than any non-seasonal depressions.
Seasonal affective disorder is estimated to affect 10 million Americans. Another 10 percent to 20 percent may have mild SAD. SAD is four times more common in women than in men. The age of onset is estimated to be between the age of 18 and 30. Some people experience symptoms severe enough to affect quality of life, and 6 percent require hospitalization. Many people with SAD report at least one close relative with a psychiatric disorder, most frequently a severe depressive disorder (55 percent) or alcohol abuse (34 percent).