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SAD During The Dark Days
One of the recent focuses of the role of solar visible light on human health and well-being has been the study of the appropriately named SAD -- Seasonal Affect Disorder (formerly Depression).
The dark, dreary days of winter have long been associated with dampening of the spirits known popularly as the "winter blues" or "winter blahs". In the past decade or two, however, there has been increasing interest in this seasonal disorder of recurrent winter depression. The usual symptoms seen in winter depression include depressed mood, increased appetite, carbohydrate craving, weight gain, increased sleep, lack of energy, and impairment of occupational and social function. Researchers originally called this Seasonal Affect Depression (SAD) but now refer to it as Seasonal Affect Disorder because we now recognize more symptoms than just depression.
With the return of high sunlight in spring and summer, however, SAD sufferers have full
remission from their symptoms and function normally. There are also milder variants of SAD
that do not result in a clinical depression. These are what we have considered the "winter blahs." Sufferers experience mostly the physical symptoms of SAD without the strong moodshifts or cognitive symptoms of depression, and their function is usually only marginally affected. Thus there is likely a spectrum of seasonality and seasonal problems in mood in the general population caused by the lack of solar intensity or duration.
Epidemiologic studies suggest that 2% to 5% of the population in northern countries like Canada suffer from significant SAD during the winter months. The prevalence of SAD appears to be more dependent on the winter day length, which gets shorter with more northern latitudes, than the local weather conditions such as the amount of sunlight during the daylight hours.
This is consistent with SAD patients who report that 1) they improve when traveling or living in a more southerly place during winter, 2) they do not return to normal mood even during good weather in the northern winter, and 3) they do not become clinically depressed during periods of poor weather in summer. However, a minority of SAD patients do seem more reactive to weather conditions, and will report marked improvement in mood during sunny days in winter and worsening during extended cloudy periods in summer and the transition seasons.
Despite active research, the pathophysiology of SAD and the mechanism of action of light therapy used to treat the disease remain elusive. However, we are recognizing that
environmental light exposure may play a very important role in the regulation of human
behaviour and rhythms and thus, the treatment of the disorder.
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