MORNING VS EVENING LIGHT TREATMENT OF PATIENTS WITH WINTER DEPRESSION

Background: According to the phase-shift hypothesis for winter depress ion, morning light (which causes a circadian phase advance) should be more antidepressant than evening light (which causes a delay). Althoug h no studies have shown evening light to be more antidepressant than m orning light, investigations have shown either no difference or mornin g light to be superior; The present study assesses these light-exposur e schedules in both crossover and parallel-group comparisons. Methods: Fifty-one patients and 49 matched controls were studied for 6 weeks. After a prebaseline assessment and a light/dark and sleep/wake adaptat ion baseline week, subjects were exposed to bright light at either 6 t o 8 AM or 7 to 9 PM for 2 weeks. After a week of withdrawal from light treatment, they were crossed over to the other light schedule. Dim-li ght melatonin onsets were obtained 7 times during the study to assess circadian phase position. Results: Morning light phase-advanced the di m-light melatonin onset and was more antidepressant than evening light , which phase-delayed it. These findings were statistically significan t for both crossover and parallel-group comparisons. Dim-light melaton in onsets were generally delayed in the patients compared with the con trols. Conclusions: These results should help establish the importance of circadian (morning or evening) time of light exposure in the treat ment of winter depression. We recommend that bright-light exposure be scheduled immediately on awakening in the treatment of most patients w ith seasonal affective disorder.