Overview of Seasonal Affective Disorder

What is Seasonal Affective Disorder?

Seasonal Affective Disorder is usually defined as recurrent fall or winter depressive episodes that remit in the spring or summer. SAD is atypical in that many of its symptoms contrast with melancholic depression. Seasonal Affective Disorder sufferers experience increased appetite, weight gain and hypersomnia. SAD was first discovered by the National Institute of Mental Health and reported in Archives of General Psychiatry in 1984.

 

What Causes Seasonal Affective Disorder?

As opposed to major depression and other affective disorders, scientists believe Seasonal Affective Disorder is a neurochemical disorder brought about by shortened winter days. Because day length causes Seasonal Affective Disorder, and because the timing of light therapy is critical for remission, researchers believe that Seasonal Affective Disorder is a result of circadian rhythm disorders. This basis in chronobiology stems from the fact that morning light has a much greater antidepressant effect, suggesting a phase delay of the shortened photoperiod. As a result, the ‘Circadian Phase-Shift Hypothesis’ is the best explanation and predictor for treating Seasonal Affective Disorder.

 

Melatonin and Seasonal Affective Disorder

Most scientists believe that darker winter days cause a circadian shift in the production of melatonin and may cause melatonin to be overproduced. This imbalance is a main reason why people feel down and depressed in the winter. Because light effectively suppresses melatonin, and because melatonin suppression is an indication of shifted circadian rhythms, light is believed to be the most effective means for treating Seasonal Affective Disorder.

 

Mechanism of Light

Light has been shown to be an ocular reaction. Light enters photoreceptors in the retina of the eye, which stimulate direct neural pathways, such as the retino-hypothalamic tract, to the Suprachaismatic Nucleus, located in the hypothalamus in the brain. The SCN in turn signals the pineal gland to stop the production of melatonin, as well as initiating other endocrine cycles. Recent findings have also shown that a specific bandwidth of light is responsible for the suppression of melatonin, and some companies are working to develop more effective products based on this research.

 

Prevalence of Seasonal Affective Disorder

An estimated 3-4%, or 11 million Americans suffer from Seasonal Affective Disorder, while up to an additional 14%, or 25 million may suffer from a milder form of Sub-syndromal Seasonal Affective Disorder or Winter Blues. The incidence of SAD is dependant on latitude. Northern areas experience shorter winter days and thus proportionately higher rates of SAD. The incidence of Seasonal Affective Disorder may be less than 2% in Florida while 10% of northern states may suffer from Seasonal Affective Disorder.

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