Seasonal affective disorder (SAD) is a mood disorder in which people who have normal mental health throughout most of the year exhibit depressive symptoms at the same time each year, most commonly in winter.
SAD was first systematically reported and named in the early 1980s by Norman E. Rosenthal, M.D., and his associates at the National Institute of Mental Health (NIMH). Rosenthal was initially motivated by his desire to discover the cause of his own experience of depression during the dark days of the northern US winter, called polar night.
SAD sufferers may exhibit any of the associated symptoms, such as feelings of hopelessness and worthlessness, thoughts of suicide, loss of interest in activities, withdrawal from social interaction, sleep and appetite problems, difficulty with concentrating and making decisions, decreased libido, a lack of energy, or agitation.
Symptoms of winter SAD often include falling asleep earlier or in less than 5 minutes in the evening, oversleeping or difficulty waking up in the morning, nausea, and a tendency to overeat, often with a craving for carbohydrates, which leads to weight gain.
In many species, activity is diminished during the winter months in response to the reduction in available food, the reduction of sunlight and the difficulties of surviving in cold weather.
Hibernation is an extreme example, but even species that do not hibernate often exhibit changes in behavior during the winter. The preponderance of women with SAD suggests that the response may also somehow regulate reproduction.
The condition in the summer 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 northern Finland, where the rate of SAD is 9.5%.
Cloud cover may contribute to the negative effects of SAD. There is evidence that many patients with SAD have a delay in their circadian rhythm, and that bright light treatment corrects these delays which may be responsible for the improvement in patients.
Although experts were initially skeptical, this condition is now recognized as a common disorder. However, the validity of SAD has been questioned by a 2016 analysis by the Center for Disease Control, in which no links were detected between depression and 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.