[Seasonal depression]

Seasonal affective disorder (SAD) is a condition characterized by annually occurring major depressive episodes which was described by Rosenthal et al. in 1984. It occurs most commonly in women and the onset usually being in early adulthood. These episodes are regularly occurring in fall and winter with full remission during the following spring and summer. The patient's mood is a combination of depression and mild anxiety accompanied by fatigue, loss of libido, and a profound reduction of socialisation. During winter depression, most of these patients complain of atypical vegetative symptoms accompanied by hypersomnia, hyperphagia, carbohydrate craving, and weight gain. Hypotheses on the underlying mechanisms of these behavioral and neurovegetative disorders indicate that environmental variables, e.g., climate, latitude, light, and changes in neurotransmitter fraction that naturally occur with the seasons may be important. Phototherapy is being increasingly used for the treatment of seasonal affective disorder. The antidepressant effect of light therapy in the treatment of SAD has been widely shown. The response in patients with SAD is contingent on the exposure of the patients' eyes to light. Further important factors are the duration of daily treatment and light intensity. However, the role of timing of phototherapy remains controversial. The biological basis of the diverse psychological and biological changes in SAD and the underlying mechanisms of action of phototherapy are still unclear and require further study.