What is Seasonal Depression?

Seasonal depression, often called seasonal affective disorder (SAD), is a depression that occurs each year at the same time, usually starting in fall, worsening in winter, and ending in spring. It is more than just "the winter blues" or "cabin fever." A rare form of SAD, known as "summer depression," begins in late spring or early summer and ends in fall.

How common is seasonal affective disorder?

Approximately half a million people in the United States suffer from winter SAD, while 10 to 20% may suffer from a more mild form of winter blues. Three-quarters of the sufferers are women, and the depression usually starts in early adulthood. SAD also can occur in children and adolescents. Older adults are less likely to experience SAD.

This illness is more commonly seen in people who live in cloudy regions or at high latitudes (locations farther north or south of the equator). Individuals who relocate to higher latitudes are more likely to be affected by SAD.

What causes seasonal affective disorder?

The exact cause of this condition is not known, but evidence strongly suggests that, for those who are vulnerable to it, SAD is set off by changes in the availability of sunlight. One theory is that with less exposure to sunlight, the internal biological clock that regulates mood, sleep, and hormones is shifted. Exposure to light may reset the biological clock.

Another theory is that brain chemicals (neurotransmitters, such as serotonin) that transmit information between nerves may be changed in people with SAD. It is believed that exposure to light can correct these imbalances.

Melatonin, a chemical known to affect sleep patterns, may also play a role in seasonal affective disorder. Some have suggested that the lack of sunlight stimulates the production of melatonin in some individuals. This may be a factor in the symptoms of sluggishness and sleepiness.

What are the symptoms of seasonal affective disorder?

People who suffer from SAD have many of the common signs of depression, including:

  • Sadness
  • Anxiety
  • Irritability
  • Loss of interest in usual activities
  • Withdrawal from social activities
  • Inability to concentrate
  • Extreme fatigue and lack of energy
  • A “leaden” sensation in the limbs
  • Increased need for sleep
  • Craving for carbohydrates, and weight gain.

Symptoms of summer SAD include:

  • Weight loss
  • Agitation and restlessness
  • Trouble sleeping
  • Decreased appetite