Latitude appears to be a significant predictor of SAD in North America; in areas that have less light during winter, the proportion of the population with SAD can be quite large. Patients with SAD are more likely to report atypical symptoms, such as hypersomnia, increased appetite, and a craving for carbohydrates.
For diagnosis of SAD, an individual should demonstrate at least two episodes of depressive disturbance in the previous 2 years, and seasonal episodes should substantially outnumber nonseasonal episodes. For people with disease susceptibility, if the sleep-wake cycle is shortened, manic symptoms ensue; if the sleep-wake cycle is lengthened, depressive symptoms ensue.
For more on the presentation of depression, read here.
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Cite this: Stephen Soreff. Fast Five Quiz: Are You Prepared to Confront Seasonal Affective Disorder? - Medscape - Nov 23, 2016.