These patient’s experience episodes of depression due to the changes in climate and amount of sunlight they are exposed to.
Recent study of an Inuit Community in Artic Canada found that 1 in 5 people were depressed and collectively 18% of the population had SAD. Another study that observed icelanders as a group found that they had low levels of SAD even when they don’t have light for many months in the winter. Scientist suggested that icelanders have lower rates of SAD because they are adapted genetically to reduced sunlight exposure.
NOTE: Reduced light causes decrease in activity of serotonin neurons of hypothalamus and these neurons are responsible in regulating behaviours such as sleep.