Arch Gen Psychiat
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Randomized Controlled Trial Comparative Study Clinical Trial
Morning vs evening light treatment for winter depression. Evidence that the therapeutic effects of light are mediated by circadian phase shifts.
Bright light exposure has been found to alleviate the symptoms of recurrent winter depression in many patients. The mechanism of light therapy may involve shifts in the timing (phase) of circadian rhythms. In this study, morning light exposure (which shifts rhythms earlier) was compared with evening light exposure (which shifts rhythms later) in a double-blind, crossover design. ⋯ At baseline, there was a trend for the onset of melatonin production to be later in the patients than in the controls. Morning light shifted the melatonin onset significantly earlier in the patients but not the controls. Our findings suggest that patients with winter depression have circadian rhythms that are abnormally delayed and that bright light therapy benefits winter depression by providing a corrective advance.