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Circadian Clock Shift May Help Seasonal Affective Disorder

Melatonin treatment allows circadian/time clock synchronization in winter

MONDAY, May 1 (HealthDay News) -- Patients with seasonal affective disorder, or SAD, may respond to treatment intended to shift their circadian rhythm to earlier in the day, according to a report published online April 28 in the Proceedings of the National Academy of Sciences Early Edition.

Alfred J. Lewy, M.D., Ph.D., from Oregon Health and Science University in Portland, and colleagues tested the hypothesis that SAD is a result of misaligned circadian rhythm and clock time or sleep/wake cycles, by giving 68 SAD patients either a placebo, melatonin in the morning to shift the circadian rhythm forward, or melatonin in the afternoon/evening to shift it back.

The investigators found that those receiving afternoon/evening melatonin had the best improvement in mood, measured by the SIGH-SAD depression score. They suggest this finding supports the hypothesis that SAD occurs due to the later sunrise in winter, shifting the circadian clock forward and out of sync with the time clock. Pushing the circadian rhythm back with melatonin realigned the two, allowing for appropriately timed bright light exposure that acts as a natural antidepressant.

"The findings support the phase-shift hypothesis for SAD, as well as suggest a way to assess the circadian component of other psychiatric, sleep and chronobiologic disorders," the authors conclude.

Lewy is co-inventor on several melatonin use-patents owned by Oregon Health and Science University.

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