SERUM CONCENTRATIONS OF THYROID-HORMONES IN PATIENTS WITH NONSEASONALAFFECTIVE-DISORDERS DURING TREATMENT WITH BRIGHT AND DIM LIGHT

Serum concentrations of thyroxine (T-4), triiodothyronine (T-3), and t hyrotropine were measured in 34 patients with nonseasonal affective di sorders before and after 1 week of light treatment, Nineteen of these patients received bright white light (2500 lx) and 15 dim red light (5 0 lx) for 2 hours daily in the mornings over a 1-week period, Slight b ut significant reductions in the rating scores for the depressive symp tomatology were found for both the bright- and dim-light groups, but t here were no significant differences between the two groups, The impro vement is thus most likely a placebo effect, Surprisingly the small ch anges in the severity of the depressive symptoms in the group as a who le were significantly correlated to the changes in the serum levels of T-4 during the weeks of bright- and dim-light treatment, respectively , The more a patient improved the further his or her T-4 level fell an d vice versa. The fluctuations in the concentrations of T-4 during lig ht treatment were significantly greater in the depressed patients than in a group of 12 healthy controls who also received bright or dim lig ht, whereas the changes in T-3 were significantly smaller than those o f the healthy controls, The pronounced fluctuations in T-4 levels were probably not secondary to changes in mood, Rather, they are likely to reflect changes in tissue (intracellular) metabolism of T-4, which ma y be involved in the mechanisms underlying the fluctuations in mood in these patients. (C) 1996 Society of Biological Psychiatry.