Seasonal Affective Disorder

What is Seasonal Affective Disorder?

Seasonal Affective Disorder is a mood disorder that is classified by depressive symptoms that occur within the same season each year, usually winter.  It is commonly thought that SAD is the result of biochemical imbalances that occur with shorter daylight hours lessening amounts of sunlight. As seasons change, people experience a shift in their biological internal clock or circadian rhythm that can cause them to be out of step with their daily schedule.  A  second, less common type of seasonal affective disorder occurs in the summer months in individuals who live in warmer climates. This type of depression is related to heat and humidity, rather than light.

It is commonly accepted that Seasonal Affective Disorder develops when a persons body cannot adapt to the limited amount of sunlight they are exposed to during the winter months of a year. One theory is that light stimulates a part of the brain called the hypothalamus, which controls your mood, sleep and appetite. This can affect how you feel.

In people with SAD, lack of sunlight and a problem with certain chemicals in the brain prevents the hypothalamus working properly. The lack of light is thought to:

  • affect the production of the hormone melatonin (the "jet lag" hormone that helps regulate bioryhythms)
  • affect the production of the hormone serotonin (a neurotransmitter that affects mood)
  • disturb your circadian rhythms (the body's internal clock that regulates several biological processes)

SAD itself occurs in both the northern and southern hemispheres, but is extremely rare in those living within 30 degrees latitude of the equator. The main age of onset of SAD is between 18 and 30 years of age.

What are the signs and symptoms of Seasonal Affective Disorder?


Symptoms usually build up slowly in the late autumn and winter months, and are usually the same as with other forms of depression:

  • Hopelessness
  • Increased appetite with weight gain (weight loss is more common with other forms of depression)
  • Increased sleep (too little sleep is more common with other forms of depression)
  • Less energy and ability to concentrate
  • Loss of interest in work or other activities
  • Sluggish movements
  • Social withdrawal
  • Unhappiness and irritability
  • Bipolar disorder or thoughts of suicide are also possible.

Signs of Spring/Summer Seasonal Affective Disorder may include:

  • Anxiety
  • Trouble sleeping (insomnia)
  • Irritability
  • Agitation
  • Weight loss
  • Poor appetite
  • Increased sex drive

What are the risk factors for Seasonal Affective Disorder? 

  • Between 60% and 90% of people with SAD are women.
    • If you are a female between 15 and 55, you are more likely to develop SAD.
  • Seasonal affective disorder appears to be more common among people who live far north or south of the equator.
    • This may be due to decreased sunlight during the winter, and longer days during the summer months.
  • As with other types of depression, those with seasonal affective disorder may be more likely to have blood relatives with the condition.
  • Those who work long hours inside office buildings with few windows may experience symptoms all year, and some individuals may note changes in mood during long stretches of cloudy weather.

 What is the treatment for Seasonal Affective Disorder?

The National Institute for Health and Care Excellence (NICE) recommends that SAD should be treated in the same way as other types of depression. This includes using talking treatments such as cognitive behavioral therapy (CBT) or medication such as antidepressants. Selective serotonin reuptake inhibitors (SSRIs) are the preferred type of antidepressants for treating SAD. They increase the level of the hormone serotonin in your brain, which helps lift your mood. 

Studies also show that between 50% and 80% of light therapy users have complete remissions of symptoms. However, light therapy must be used for a certain amount of time daily and continue throughout the dark, winter months.

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