Seasonal affective disorder (SAD) is a type of depression. It is associated with the seasonal changes in light. SAD most commonly occurs in late fall and lasts through the winter and into spring. SAD is more than feeling down, it interferes with normal daily functions during these times.

Brain—Psychological Organ
Brain face skull
SAD may be caused by fluctuations in hormones and brain chemicals.
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The causes of SAD are not completely clear. Some factors that may play a role include:

  • Reduced sunlight—This affects internal clocks, readjusting hormones and brain chemicals.
  • Increase in melatonin production—Melatonin may cause symptoms of depression. This hormone is produced in higher amounts in the dark.
  • Low serotonin—Serotonin is a brain chemical that is associated with well-being. In people with SAD, there may be a lack of serotonin in the brain.