Seasonal affective disorder (also known as winter depression, winter blues or simply SAD) is a mood disorder in which people who have normal mental health throughout most of the year, experience depressive symptoms in the winter or, less frequently, in the summer, spring or autumn, repeatedly, year after year. SAD is not a unique mood disorder, but is "a specifier of major depression". Once regarded skeptically by the experts, seasonal affective disorder is now well established. Studies estimate that its prevalence in the adult population of the US ranges from 1.4 percent (Florida) to 9.7 percent (New Hampshire).
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