LIGHT THERAPY IN SEASONAL AFFECTIVE-DISORDER IS INDEPENDENT OF TIME OF DAY OR CIRCADIAN PHASE

Objective: We tested the hypothesis that phase-delayed circadian rhyth ms underlie seasonal affective disorder (SAD) by measuring phase posit ion of 6-sulfatoxymelatonin excretion and comparing antidepressant res ponse to morning or evening light given as a first treatment. Design: Randomized controlled trial. Setting: Ambulatory. Patients: Thirty-two women and seven men with SAD. Intervention: Light therapy (2500 lux f or 1 hour for 1 week) was administered either at 7 AM or 10 PM, preced ed by a baseline week and followed by a withdrawal week. Results: Our SAD patient sample was moderately depressed (Hamilton Depression Scale [HAM-D] score 18); a HAM-D reduction of 50% or more was found in 12 o f 18 patients given morning and in 15 of 21 patients given evening lig ht (70% response rate). Response was not dependent on age, gender, sta ge of the menstrual cycle, time of year, or on the timing or duration of sleep. Urinary 6-sulfatoxymelatonin was measured in 30 patients; 22 had phase-delayed circadian rhythms. However, phase position was corr elated neither with depth of depression nor with a preferential respon se to morning or evening light. Comment:Both morning and evening light therapy improved depressive symptoms in patients with SAD independent of their circadian phase or sleep timing. These findings argue agains t a circadian phase-delay hypothesis of the pathophysiology of SAD, or the necessity of a phase-advance by morning light for clinical effica cy. They additionally suggest more practicable and flexible schedules for light therapy in SAD, since time of day is not crucial.