Seasonal affective disorder: an overview

Chronobiol Int. 2003 Mar;20(2):189-207. doi: 10.1081/cbi-120019310.


Seasonal Affective Disorder (SAD) is a condition of regularly occurring depressions in winter with a remission the following spring or summer. In addition to depressed mood, the patients tend to experience increased appetite and an increased duration of sleep during the winter. SAD is a relatively common condition, affecting 1-3% of adults in temperate climates, and it is more prevalent in women. The pathological mechanisms underlying SAD are incompletely understood. Certain neurotransmitters have been implicated; a dysfunction in the serotonin system in particular has been demonstrated by a variety of approaches. The role of circadian rhythms in SAD needs to be clarified. The phase-delay hypothesis holds that SAD patients' circadian rhythms are delayed relative to the sleep/wake or rest/activity cycle. This hypothesis predicts that the symptoms of SAD will improve if the circadian rhythms can be phase-advanced. There is some experimental support for this. SAD can be treated successfully with light therapy. In classical light therapy, the SAD sufferer sits in front of a light box, exposed to 2000-10,000 lux for 30-120 min daily during the winter. Other forms of light treatments, pharmacotherapy, and other therapies are currently being tested for SAD.

Publication types

  • Review

MeSH terms

  • Chronobiology Phenomena
  • Circadian Rhythm
  • Humans
  • Melatonin / physiology
  • Models, Biological
  • Photoperiod
  • Phototherapy
  • Seasonal Affective Disorder* / etiology
  • Seasonal Affective Disorder* / physiopathology
  • Seasonal Affective Disorder* / therapy
  • Seasons
  • Serotonin / physiology


  • Serotonin
  • Melatonin