Thyroid function before and after four-week light treatment in winter depressives and controls.

Thyroid function in patients in a current major depressive episode during the course of recurrent major mood disorder with seasonal pattern according to DSM-IIIR was compared to that of controls before and after 4 weeks' light treatment, and to that of controls at baseline and after 4 weeks' of arising early without exposure to bright light. No consistent abnormalities in thyroxine, free thyroxine index, triiodothyronine, reverse triiodothyronine, thyrotropin, thyrotropin response to TRH infusion, or thyroid autoantibodies were seen in depressives at baseline. No differences in these parameters were seen at baseline between depressives and controls. No intergroup differences were seen with treatment, although reverse T3 decreased significantly during the protocol in all groups. These data do not support the hypothesis that the thyroid axis plays a role in the pathogenesis of winter depressive symptoms or their response to light treatment.