EFFECTS OF MORNING PHOTOTHERAPY ON CIRCADIAN MARKERS IN SEASONAL AFFECTIVE-DISORDER

Background The suppression of melatonin by light at 00.30 hours has be en shown to be greater in winter than in summer in patients with seaso nal affective disorder (SAD) but not in matched normal controls. Metho d In this study 12 patients with SAD and 12 matched normal controls we re exposed to morning light therapy in the winter. Melatonin profiles and sensitivity to light were measured before and after treatment. Res ults The SAD but not the normal group showed a phase advance of melato nin rhythms in response to phototherapy. There was an association betw een phase position and phase shift in the SAD but not in the normal gr oup. Conclusions There may be instability of circadian rhythms in SAD mediated by a high-amplitude phase response curve, rather thana fixed phase abnormality as had been previously suggested. This instability m ay be secondary to impaired serotoninergic function in the afferent pa thways to the suprachiasmatic nuclei.