Seasonal Affective Disorder (Causes)

Seasonal Affective Disorder, or SAD, is a depression that normally occurs in winter months, in response to changes in the natural day/night cycle. Artificial light therapy is an effective treatment.

The cause for SAD is unknown. One theory is that it is related to the amount of melatonin in the body, a hormone secreted by the pineal gland. The body is exposed to its secretions for a shorter period of time during summer because light suppresses it production. The long nights of winter extends the amount of time melatonin is released into the body, thus increasing symptoms. It is not clear how melatonin produces the symptoms reported. One possible explanation is that melatonin causes a drop in body temperature and lower body temperature is associated with sleep. This could indicate that it is related to the sleep-wake cycle and related to the hypersomnia and fatigue reported.

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