Seasonal Affective Disorder is characterized by a fall-winter depression and a spring-summer remission. An estimated 10-to-20 percent of cases with depression follow this pattern. The prevalence of SAD is higher in New Hampshire and lower in Florida. Research has demonstrated that in North America the prevalence of SAD increases with latitude.
Young adults and women are more likely to have SAD, but it has been identified in children and adolescents as well. Interestingly, seasonality has been identified in other psychiatric disorders such as bulimia and anxiety disorders.
The etiology of SAD has not been completely determined. It is known that the turnover of seratonin in the human brain is lowest in the winter seasons, and the rate of seratonin production increases with sunshine brightness and exposure.
The most widely used and investigated treatment of SAD is light therapy. Light therapy involves daily exposure to a box containing fluorescent lamps during symptomatic months. The exposure is usually in the morning, although some see improvement with both a morning and an evening exposure. The recommended duration varies from thirty minutes to two hours per day for at least two-to-four weeks. Medications such as antidepressants can also be used in addition to light therapy. Other medication such as modafinil and propanolol have also been researched in the treatment of SAD.
SAD likely results from a complex interplay of environmental, biological and psychological factors. Light therapy has emerged as an established treatment for this interesting disorder.