Seasonal affective disorder (SAD) is a type of depression that is tied to seasons of the year. Most people with SAD are depressed only during the late fall and winter (sometimes called the "winter blues") and not during the spring or summer. A small number, however, are depressed only during the late spring and summer.


SAD is most common in young adult women, although it can affect men or women of any age. In North America, SAD may affect as many as 6 of every 100 people, more in the Northern portions of the country than in the South. Another 10-20% of people may have a milder form of seasonal mood change.


Like all types of depression, SAD can have a devastating effect on a person’s life. Fortunately, almost all people with SAD can be helped with available therapies.


Seasonal affective disorder (SAD) may have some of the same symptoms as other types of depression. 


  • Most people have only some of these symptoms, not all.

       - Depressed mood.

       - Loss of interest in usually enjoyable activities.

       - Fatigue or loss of energy.

       - Feelings of worthlessness or hopelessness.

       - Poor concentration, indecisiveness.

       - Recurrent thoughts of death or suicide.

  • The symptoms of SAD come back every year, and for any specific person, they tend to come and go at about the same time each year.
  • Winter SAD.

       - Sleeping more than usual.

       - Craving for sugar, starchy foods, or alcohol.

       - Weight gain.

       - Irritability.

       - Conflicts with other people.

       - Heaviness of arms and legs.

       - Behavior disturbances (in children).

  • People with winter SAD may seek out light places or sunlight, or like to have lots of artificial lights on.
  • Summer SAD.

       - Insomnia.

       - Poor appetite.

       - Weight loss.

       - Agitation.

       - Anxiety.


Seasonal affective disorder seems to develop from inadequate bright light during the winter months. Researchers have found that bright light changes the chemicals in the brain. Exactly how this occurs and the details of its effects are being studied.


While those specific mechanisms remain undetermined, factors like low vitamin D levels in the blood are found to be associated with a higher occurrence of seasonal affective disorder and some other depressive disorders.

The exact causes of seasonal affective disorder (SAD) are unknown.


  • Chemical changes in the brain caused by changes in the amount of sunlight are probably involved. People who live in geographical locations that are dark or cloudy during the winter are most likely to have SAD.
  • A tendency to have SAD may run in some families.


In addition to being key in the prevention of seasonal affective disorder, regular exposure to light that is bright, particularly fluorescent lights, significantly improves depression in people with this disorder when it presents during the fall and winter. The light treatment is used daily in the morning and evening for best results.


Temporarily changing locations to a climate that is characterized by bright light (such as the Caribbean) can achieve similar results. Light treatment has also been called phototherapy. Individuals who suffer from seasonal affective disorder will also likely benefit from increased social support during vulnerable times of the year.


Phototherapy is commercially available in the form of light boxes, which are used for approximately 30 minutes daily. The light required must be of sufficient brightness, approximately 25 times as bright as a normal living room light.


Contrary to prior theories, the light does not need to be actual daylight from the sun. It seems that it is quantity, not necessarily quality of light that matters in the light therapy of seasonal affective disorder. The most common possible side effects associated with phototherapy include irritability, insomnia, headaches, and eyestrain.


Antidepressant medications, particularly those from the serotonin selective reuptake inhibitor family (SSRI) family, have been found effective treatment for seasonal affective disorder that presents during summer as well as that which tends to occur during the fall or winter. Examples of SSRIs includefluoxetine (Prozac), sertraline (Zoloft), paroxetine (Paxil) and citalopram (Celexa).


Common side effects for this class of medications include insomnia, nausea, diarrhea, and decreased sex drive or performance. As with any other mood disorder, psychotherapy tends to accentuate the effectiveness of medical treatment and therefore should be included in the approach to addressing this disorder. In individuals who are perhaps vulnerable to the development of bipolar disorder, either light therapy or antidepressant medication can cause a manic episode as a side effect.


Since stimulant medications like modafinil (Provigil) may be a helpful addition to other treatments for seasonal affective disorder, other stimulants like methylphenidate (Ritalin) may play a future role in addressing this disorder.


Acupuncture may be a viable alternative intervention to antidepressant medications, particularly in pregnant women, for whom medications should be used with particular caution.

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