Proposed causes of winter depression include decrease in amount of sunlight, inability to suppress melatonin production, and finally disruption of circadian rhythms related to sleep/wake cycle in susceptible individuals. Like seasonal effect of sunlight on mood, the mood is also correlated with sunshine hours. The amount of sunlight reaching the brain from the eyes via retinohypothalamic tract is reduced in sunglass users, because sunglasses screen out 75% to 90% of visible light. In people wearing sunglasses, the antidepressant effect of sunlight may be reduced and circadian rhythms may be distorted, possibly leading to the emergence winter depression. Since the sunlight has antidepressant effect and since sunglasses reduce sunlight exposure, we hypothesized that sunglass use may play a role in depression.
Key words: depression, sunglasses; vitamin D
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