Seasonal affective disorder (SAD)

What is SAD?
An estimated 2% to 3% of the general population suffers from seasonal affective disorder (SAD), a type of depression that seems to be related to the amount of sunlight that you are exposed to. An extreme form of the "winter blues," SAD is worst for most people in the fall and winter. In rare cases, some people develop SAD during the late spring or early summer months. If you have episodes of depression that recur at the same time every year for more than 2 years, you may have SAD, and not just the occasional winter blues.

SAD is a real medical condition that can affect anyone, even people who are not already predisposed to depression. The condition is more common in women than in men. Most people who develop SAD start experiencing symptoms between the age of 18 and 30. Most people with SAD live in northern climates where there are shorter days in the winter months. Their symptoms begin to lessen in the spring when the amount of sunlight increases each day.

What are the symptoms of SAD?
People with SAD feel tired and lethargic and may withdraw from friends and family. They may have less interest in activities that they usually enjoy. Other symptoms include the following:

  • inability to concentrate
  • sadness or despair
  • increased appetite, cravings for sweet and starchy foods, and weight gain (usually occurring in the winter months)
  • irritability
  • increased sleepiness
  • lack of energy
  • decreased interest in work and social activities

Many symptoms of SAD are similar to those of major depression. Talk to your doctor if you are experiencing some or all of the symptoms listed above.

What causes SAD?
While the exact cause of SAD is unknown, researchers believe the condition may be related to the body's internal clock, which regulates temperature and hormone production. Nerve centers in the brain control our daily moods and rhythms and are stimulated by the amount of light that enters our eyes.

During the night and in periods of reduced light (as occurs in the winter), a gland in the brain produces a hormone called melatonin, which makes you feel drowsy. SAD may be related to increased levels of melatonin in the body. On dull winter days, people with the condition may have difficulty waking up, and may feel drowsy or "down" during the day.

Other research is looking at the role of serotonin in SAD. Serotonin is a neurotransmitter (chemical in the brain) that helps to regulate mood and behaviour. Sunlight seems to have an effect on serotonin levels. Therefore, the shorter days and longer nights associated with the fall and winter season may cause decreased levels of serotonin.

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