Seasonal depression disorder, also known as seasonal affective disorder or SAD disorder, is a form of depression that affects about 6 percent of the U.S. population, according to Psychology Today magazine. This condition typically occurs during times of the year when daylight is limited. The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) states that SAD disorder is not a condition in its own right, but rather a subset of major depressive or bipolar disorders.

Winter Blues

Seasonal depression most often manifests as “winter blues,” or recurrent episodes of depression during the late fall and winter. Symptoms of winter blues include:

  • Anxiety
  • Depression
  • Fatigue
  • Hopelessness
  • Loss of interest in normally enjoyable activities
  • Oversleeping (almost like hibernating)
  • Social withdrawal
  • Weight gain, as a result of craving foods high in carbohydrates.

Seasonal Depression in the Summer

Occasionally, an individual might experience summer seasonal affective disorder, or signs of depression in the summertime. Symptoms of seasonal depression disorder in the summer include:

  • Agitation
  • Anxiety
  • Increased sex drive
  • Insomnia
  • Irritability
  • Weight loss.

Seasonal Depression Causes

Although the exact cause of seasonal depression disorder is still a mystery, scientists have focused their research on three major theories:

  • Circadian rhythm: This is the physiological process that regulates a body’s internal clock. A reduced level of sunlight in the fall or winter can disrupt this rhythm, resulting in fall or winter “blues.”
  • Melatonin: Most studies have shown a link between the SAD disorder and melatonin, a sleep-related hormone. Since the body tends to produce more melatonin during the winter periods, a person may tend to oversleep during the winter, a symptom of seasonal depression.
  • Serotonin: Other research has found a link between seasonal depression and serotonin, a natural brain chemical that affects a person’s mood. Reduced sunlight appears to decrease a person’s serotonin levels, resulting in the depressive state associated with the SAD disorder. Low vitamin D levels are also linked to low serotonin. Increased exposure to sunlight actually increases the amount of vitamin D in the body.

Genetics and Seasonal Depression Disorder

Some studies have shown that people affected by seasonal depression are more likely to have family members with the same condition, especially if they are twins.

Researchers have discovered two particular genes in seasonal depression sufferers that differ from the general population. The 5-HTTLPR and 5-HT2A genes are both involved in the production of serotonin. The presence of the gene confirms the depressive symptoms of seasonal depression disorder, but it doesn’t explain why these symptoms manifest during certain seasons.

A recent study has shown that a mutation in the melanopsin gene may also be linked to seasonal depression. Melanopsin is a photopigment that affects circadian rhythms as well as other non-visual responses in the eye.

SAD Disorder Treatment

Luckily, seasonal depression disorder is treatable. Doctors may prescribe medication or suggest psychotherapy. Other types of therapy expose patients to bright light that mimics outdoor light in order to regulate circadian rhythms. These treatments include:

  • Dawn stimulation
  • Light box therapy
  • Negative ion therapy.


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Mayo Clinic Staff. (n.d). Seasonal affective disorder (SAD) definition. Retrieved December 14, 2008, from the Mayo Clinic website:

Mayo Clinic Staff. (n.d). Seasonal affective disorder (SAD) symptoms. Retrieved December 14, 2008, from the Mayo Clinic website:

Mayo Clinic Staff. (n.d). Seasonal affective disorder (SAD) treatments and drugs. Retrieved December 14, 2008, from the Mayo Clinic website:

Psychology Today Staff. (n.d.). Seasonal affective disorder. Retrieved April 20, 2010, from the Psychology Today website:

 Posted on : June 26, 2014