[Seasonal depression]

Seasonal affective disorder (SAD) is characterized by annual major depressive episodes. It occurs most commonly in young women during autumn and winter with full remission during the following spring. The patient's mood is a combination of depression and anxiety accompanied by fatigue, loss of libido, and a reduction of socialization. Most of these patients complain of atypical vegetative symptoms (e.g. hypersomnia, carbohydrate craving, and weight gain). Hypotheses on the underlying mechanisms of these behavioural disorders indicate that environmental variables, e.g. climate, latitude, light, and changes in neurotransmitter function that occur naturally with the seasons, may be important. Phototherapy is being used increasingly for the treatment of SAD. The antidepressant response is contingent on the exposure of the patients' eyes to light. The biological basis of the diverse psychological and biological changes in SAD and the underlying mechanism of action of phototherapy are still unclear and require further study.