Seasonal affective disorder

Seasonal affective disorder (SAD) is a mood disorder subset in which people who typically have normal mental health throughout most of the year exhibit depressive symptoms at the same time each year. It is commonly, but not always, associated with the reductions or increases in total daily sunlight hours that occur during the winter or summer.

Common symptoms include sleeping too much, having little to no energy, and overeating. The condition in the summer can include heightened anxiety. However, there are significant differences in the duration, severity, and symptoms of each individual's experience of SAD. For instance, in a fifth of patients, the disorder completely resolves in five to eleven years, whereas for 33-44% of patients, it progresses into non-seasonal major depression.

In the DSM-IV and DSM-5, its status as a standalone condition was changed: It is no longer classified as a unique mood disorder but is now a specifier (called "with seasonal pattern") for recurrent major depressive disorder that occurs at a specific time of the year and fully remits otherwise. Although experts were initially skeptical, the condition eventually became recognized as a common disorder. However, the validity of SAD was called into question by a 2016 analysis from the Centers for Disease Control, when it found no links between depression, seasonality or sunlight exposure.

In the United States, the percentage of the population affected by SAD ranges from 1.4% of the population in Florida to 9.9% in Alaska.