[Light therapy of patients with seasonal affective disorder]

Numerous investigators have shown a strong association between the seasons and the incidence of depression, mania and suicides. However, little has been known about patients who reveal affective episodes in association with the changing seasons year after year. Lewy and Rosenthal established the concept of Seasonal Affective Disorder (SAD). SAD is characterized by recurring cycles of fall-winter depression and spring-summer hypomania (or euthymia). Depressive symptoms often include hypersomnia, anergia, fatigue, carbohydrate craving and weight gain. The syndrome occurs predominantly in women and begins in late twenties. Lewy, Rosenthal and other investigators found that exposure of the SAD patients to bright artificial light improved depressive symptoms. Some hypotheses of light therapy are proposed, however, each of them has not well explained the mechanisms.