Seasonal affective disorder

Seasonal affective disorder (SAD) is characterized by annual major depressi ve episodes. It occurs most commonly in young women during autumn and winte r with full remission during the following spring. The patient's mood is a combination of depression and anxiety accompanied by fatigue, loss of libid o, and a reduction of socialization. Most of these patients complain of aty pical vegetative symptoms (e.g. hypersomnia, carbohydrate crating, and weig ht gain). Hypotheses on the underlying mechanisms of these behavioural diso rders indicate that environmental variables, e.g. climate, latitude, light, and changes in neurotransmitter function that occur naturally with the sea sons, may be important. Phototherapy is being used increasingly for the tre atment of SAD. The antidepressant response is contingent on the exposure of the patients' eyes to light. The biological basis of the diverse psycholog ical and biological changes in SAD and the underlying mechanism of action o f phototherapy are still unclear and require unclear study.