Seasonal Affective Disorder



  • Seasonal affective disorder (SAD) describes mood episodes that occur as a part of major depressive or bipolar disorder in a seasonal pattern. Patients may experience depressive, hypomanic, or manic episodes, although depression is more common.
  • Depressive episodes typically occur during winter months (fall-winter onset), with full remission in the spring and summer. Less commonly, patients may experience a spring-summer onset with remission in the fall-winter months.
  • Ranges from a milder form (winter blues) to a seriously disabling illness



  • Affects up to 500,000 Americans every winter
  • Up to 30% of patients visiting a primary care physician (PCP) during winter may report winter depressive symptoms.
  • Predominant age: occurs at any age; peaks in 20s and 30s
  • Predominant sex: female > male (3:1)


  • Lifetime prevalence of the general population is 0.5–3%.
  • Point prevalence in primary care patients is 5–10%, while in depressed patients, this is 15%.

Etiology and Pathophysiology

  • The major theories currently involve the interplay of phase-shifted circadian rhythms, genetic vulnerability, and serotonin dysregulation.
  • Photoperiod and Phase Shift Hypotheses:
    • During the winter months, the period of natural daylight is shorter. When there is less sunlight, the pineal gland increases melatonin secretion, which can lead to a phase shift in circadian rhythm. This process has been linked to symptoms of depression. Light therapy in the morning or evening can suppress melatonin secretion to correct the phase shift and improve symptoms of depression. Reduced sunlight may also decrease vitamin D levels, which may contribute to symptoms of depression.
  • Serotonin Dysregulation Hypothesis:
    • It is suspected that dysregulation of serotonin, particularly increased clearance from the synaptic cleft and reduced secretion, contributes to SAD pathophysiology. Central acting serotonergic agents such as SSRIs appear to reverse SAD symptoms.


  • Twin studies and a preliminary study on GPR50 melatonin receptor variants suggest a genetic component.
  • Studies also indicate an association with melanopsin gene (OPN4) variants.
  • Increased incidence of depression, ADHD, and alcoholism in close relatives, or first-degree relatives with SAD increase the chance an individual will develop SAD.

Risk Factors

  • Most common during months of January and February: Patients frequently visit their PCP during winter months complaining of recurrent flu, chronic fatigue, and unexplained weight gain.
  • Working in a building without windows or other environments without significant exposure to sunlight

General Prevention

  • Consider use of light therapy at the start of winter (if prior episodes begin in October), increase time outside during daylight hours, or move to a more southern location.
  • Bupropion (Wellbutrin) is the only FDA-approved antidepressant for the prevention of SAD.
  • While studies show mixed results, low-dose melatonin in the evening may help prevent symptoms of depression from occurring if taken before and during winter months.

Commonly Associated Conditions

Patients with SAD often have other comorbid psychiatric disorders including alcohol use disorder, ADHD, and binge eating disorder, among others. Some individuals with SAD have a weakened immune system and may be more vulnerable to infections.

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